JP6665550B2 - Tire contact surface analysis device, tire contact surface analysis system, and tire contact surface analysis method - Google Patents

Description

  The present invention relates to a tire contact surface analysis device, a tire contact surface analysis system, and a tire contact surface analysis method.

  2. Description of the Related Art A pneumatic tire (hereinafter, simply referred to as a "tire") comes into contact with a moving body such as a vehicle to move on a target surface, for example, a road surface. It is the only one that transfers power from the source to the target surface. Therefore, the performance of the tire has a great influence on the kinetic performance of the vehicle. Tire performance includes, for example, evaluation items such as noise performance, friction performance, steering stability performance, and braking performance, and these evaluation items change depending on tire contact characteristics. The tire contact characteristics include a contact area, an average pressure based on a load applied and a contact area, a maximum contact length in a tire circumferential direction (contact length direction), and a maximum contact width in a tire width direction (contact width direction). In order to accurately determine these tire contact characteristics, the tire contact shape when the tire comes into contact with the target surface, particularly the contour line that constitutes the tire contact surface when the tire comes into contact with the target surface, is determined, and the contact area is determined. It is important to obtain the value with high accuracy.

  Therefore, conventionally, a technique has been proposed in which image analysis of tire contact image data is performed to determine a tire contact shape, and a tire contact characteristic is determined. For example, Patent Document 1 discloses that a captured image of a tire tread is binarized based on a threshold set for luminance, and an inflating process and an eroding process are performed on the binarized image. A technique for determining a ground contact shape is described.

JP-A-5-196557

  Here, when the analysis of the contact area is obtained by determining the tire contact shape, not only the shape of the entire contact area, but also the contact area excluding the groove shape from the total contact area including the groove portion, that is, actually contact the ground. The shape of the actual ground area is also an important factor. The shape of the actual contact area can be extracted by excluding the groove shape from the image of the total contact area. The groove shape can be extracted by binarizing the contact image based on luminance. it can. In other words, in the grounding image, since the luminance is different between the portion of the tread surface where the ground is actually grounded and the portion of the groove, the shape of the groove can be extracted by binarizing the grounding image based on the luminance. it can.

  On the other hand, the tread surface of the tire may be provided with an engraved mark for identifying the type of the member at the time of manufacturing the tire, a marking written at the time of testing the tire, and the like. The markings and markings on the tread surface often differ in luminance from the unmarked parts, so if the groove shape is extracted based on the luminance, the markings and other parts are similar to the grooves. It may be extracted differently from the actual state of the actual ground area, such as being extracted as an element. Therefore, when the tread surface is engraved or the like, there is a problem that the analysis accuracy when analyzing the ground contact area is reduced.

  The present invention has been made in view of the above, and provides a tire tread analysis device, a tire tread analysis system, and a tire tread analysis method capable of reducing an analysis error in analyzing a tread region. The purpose is to:

  In order to solve the above-described problems and achieve the object, a tire contact surface analysis device according to the present invention includes a contact surface image acquisition unit that acquires an image of a contact surface of a pneumatic tire, and the contact surface image acquisition unit. A groove extracting unit that extracts a groove of the pneumatic tire from the acquired ground contact surface image, wherein the groove extracting unit sets a scan line on the ground contact surface image, and the scan line In the case where the average luminance in the region where is located is the land local luminance, and a value obtained by subtracting a certain value from the land local luminance is the groove local luminance, the luminance of the center pixel of the scan line and the groove are obtained. A brightness comparison unit that compares the local brightness, and when the brightness of the center pixel is smaller than the groove local brightness, a brightness differential profile of the ground plane image in a range where the scanning line is located is generated. Extracting a maximum point having a luminance differential value equal to or greater than a predetermined threshold value from the luminance differential profile, and extracting the local maximum point from the central pixel on each of both sides in the length direction of the scanning line with the central pixel interposed therebetween. A determination unit that determines a region sandwiched between the two closest local maximum points as the groove.

  Further, in the tire ground contact surface analysis device, the scan line setting unit includes, as the scan line, a circumferential scan line set in a direction extending along a tire circumferential direction of the pneumatic tire; It is preferable to set a width direction scanning line set in a direction extending along the tire width direction.

  Further, in the tire ground contact surface analysis device, the scan line is longer than twice the maximum width of the width of the groove intersecting the scan line in the contact surface image in the length direction of the scan line. It is preferable to set the distance.

  In the tire contact surface analysis device, it is preferable that the threshold value is 1.25 times or more and 2.5 times or less of an average luminance differential in a total contact region included in the contact surface image.

  The tire contact surface analysis device further includes a contour emphasized image generating unit configured to generate a contour emphasized image in which a contour in the image is emphasized by differentiating the luminance of the contact surface image, wherein the luminance differential profile Is preferably generated using the outline emphasized image.

  In the tire contact surface analysis device, a total contact region calculation unit that determines a total contact region from the contact surface image, and the total contact region determined by the total contact region calculation unit, extracted by the groove extraction unit. And a real ground contact area calculation unit that obtains the real ground contact area by removing the groove.

  Further, in order to solve the above-described problems and achieve the object, a tire contact surface analysis system according to the present invention includes the tire contact surface analysis device, a transparent plate for pressing the pneumatic tire, and pressing the transparent plate. A plurality of light sources for irradiating the ground plane, and a photographing unit for photographing the ground plane via the transparent plate.

Further, to solve the problem described above and achieve the object, a tire contact surface analysis method according to the present invention includes the steps of acquiring an image of the ground surface of the pneumatic tire, the scan line with respect to contact the ground image Setting the average luminance in the area where the scanning line is located as the land local luminance, and subtracting a constant value from the land local luminance as the groove local luminance, the scanning line, Comparing the luminance of the central pixel with the local luminance of the groove, and when the luminance of the central pixel is smaller than the local luminance of the groove, a luminance differential profile of the ground plane image in a range where the scanning line is located. And extracting a local maximum point having a luminance differential value equal to or greater than a predetermined threshold from the luminance differential profile, and scanning the central pixel among the local maximum points with the central pixel interposed therebetween. And determining in the area sandwiched in by the maximum point of the two nearest points to the center pixel in each sides length direction groove of the pneumatic tire, characterized in that it comprises a.

  ADVANTAGE OF THE INVENTION The tire contact surface analysis apparatus, the tire contact surface analysis system, and the tire contact surface analysis method according to the present invention have an effect that an analysis error in analyzing a contact region can be reduced.

FIG. 1 is a configuration diagram illustrating a tire ground contact surface analysis system according to the embodiment. FIG. 2 is a block diagram illustrating functions of the tire tread surface analysis device illustrated in FIG. 1. FIG. 3 is a flowchart showing a processing procedure when analyzing the contact surface with the tire contact surface analysis device according to the embodiment. FIG. 4 is an explanatory diagram of a ground contact surface image. FIG. 5 is an explanatory diagram of the ground contact surface image on which the noise removal processing has been performed. FIG. 6 is an explanatory diagram of a median filter. FIG. 7 is an explanatory diagram of weights used in the Gaussian filter. FIG. 8 is an explanatory diagram of a contour line emphasized image. FIG. 9 is an explanatory diagram of a Sobel filter when weighting pixels in the vertical direction. FIG. 10 is an explanatory diagram of a Sobel filter when weighting pixels in the horizontal direction. FIG. 11 is an explanatory diagram in the case where the absolute value of the luminance derivative is calculated using the filter shown in FIG. FIG. 12 is an explanatory diagram in the case where the absolute value of the luminance derivative is calculated using the filter shown in FIG. FIG. 13 is a flowchart showing the processing procedure for extracting a groove. FIG. 14 is an explanatory diagram of a scanning line. FIG. 15 is a flowchart illustrating a processing procedure for performing the groove extraction processing. FIG. 16 is a detailed view of a portion A in FIG. FIG. 17 is an explanatory diagram of the center pixel. FIG. 18 is a detailed view of the contour-line emphasized image at the same position as the ground contact surface image shown in FIG. FIG. 19 is an explanatory diagram of a luminance differential profile. FIG. 20 is an explanatory diagram showing a state where a scanning line is located at a portion where no marking is given. FIG. 21 is a detailed view of the contour line emphasized image at the same position as the ground contact surface image shown in FIG. FIG. 22 is an explanatory diagram of a luminance differential profile. FIG. 23A is an explanatory diagram of how a scanning line advances. FIG. 23B is an explanatory diagram of how a scanning line advances. FIG. 23C is an explanatory diagram of how a scanning line advances. FIG. 23D is an explanatory diagram of how a scanning line advances. FIG. 23E is an explanatory diagram of how a scanning line advances. FIG. 24A is an explanatory diagram of how a scanning line in the width direction advances. FIG. 24B is an explanatory diagram of how the scanning line in the width direction advances. FIG. 24C is an explanatory diagram of how the scanning line in the width direction advances. FIG. 24D is an explanatory diagram of how the scanning line in the width direction advances. FIG. 24E is an explanatory diagram of how the scanning line in the width direction advances. FIG. 25 is an explanatory diagram of the ground area image generated based on the luminance. FIG. 26 is an explanatory diagram of the total contact area image. FIG. 27 is an explanatory diagram of the expansion processing. FIG. 28 is an explanatory diagram of the contraction processing. FIG. 29 is an explanatory diagram of a groove image. FIG. 30 is an explanatory diagram of the groove image after performing the contraction processing and the expansion processing. FIG. 31 is an explanatory diagram of the actual ground area image. FIG. 32 is an explanatory diagram of the luminance at the position of the scanning line shown in FIG. FIG. 33 is an explanatory diagram of a scanning line located in a portion where no groove exists. FIG. 34 is an explanatory diagram of the luminance at the position shown in FIG. FIG. 35 is an explanatory diagram of a luminance differential scanning line at a position corresponding to FIG. FIG. 36 is an explanatory diagram of the luminance differential profile at the position shown in FIG. FIG. 37 is an explanatory diagram illustrating a state where the pixel of the center pixel is lower than the luminance cut line. FIG. 38 is an explanatory diagram showing a state in which a scanning line is set on a summer tire. FIG. 39 is an explanatory diagram of luminance at the position shown in FIG. FIG. 40 is an explanatory diagram of the luminance differential profile at the position shown in FIG.

  Hereinafter, embodiments of a tire contact surface analysis device, a tire contact surface analysis system, and a tire contact surface analysis method according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited by the embodiment. In addition, constituent elements in the following embodiments include those that can be easily replaced by those skilled in the art, and those that are substantially the same.

[Embodiment]
FIG. 1 is a configuration diagram illustrating a tire ground contact surface analysis system according to the embodiment. FIG. 2 is a block diagram illustrating functions of the tire tread surface analysis device illustrated in FIG. 1. In these figures, FIG. 1 schematically shows the entire configuration of the tire contact surface analysis system, and FIG. 2 shows main functions of the tire contact surface analysis device.

  The tire tread analysis system 1 according to the present embodiment is applied to a system that analyzes the tread 61 by acquiring an image of the tread 61 of the pneumatic tire. The tire contact surface analysis system 1 includes a tire testing machine 2, an imaging device 10, and a tire contact surface analysis device 20 (see FIG. 1).

  The tire testing machine 2 is a device that gives test conditions to a test tire 60 that is a pneumatic tire to be tested. In the configuration of FIG. 1, the tire testing machine 2 has a supporting device 3 and a driving device 5. The support device 3 is a device that rotatably supports the test tire 60 and has a rim 4 on which the test tire 60 is mounted. The driving device 5 is a device for applying a driving force to the test tire 60, and includes a motor 6 for driving the test tire 60 and a motor control device 7 for driving and controlling the motor 6.

  In the tire testing machine 2, the supporting device 3 mounts and supports the test tire 60 on the rim 4, and presses the test tire 60 against the upper surface 11 </ b> U, which is one main surface of the transparent plate 11 of the driving device 5. A load is applied to 60. In addition, the support device 3 adjusts the positional relationship between the test tire 60 and the transparent plate 11 by displacing the rim 4 to give the test tire 60 a slip angle or an angle. The drive device 5 can drive the motor 6 by the motor control device 7 to rotate the rim 4 by a predetermined angle. Thereby, the rolling state of the tire when the vehicle is running is reproduced with the surface of the transparent plate 11 as the road surface. Further, the test conditions can be changed by adjusting the load, the rotational speed, the slip angle, the angle, and the like by the support device 3 and the drive device 5.

  The transparent plate 11 is a light transmitting plate having a property of transmitting light. The transparent plate 11 does not need to transmit 100% of the light, and it is sufficient that the transparent plate 11 has a light transmittance that allows the surface of the tire to be photographed through the transparent plate 11. The transparent plate 11 is, for example, a flat plate made of acrylic resin or a flat plate made of glass. Since the contact state between the test tire 60 and the flat plate is photographed and image-analyzed, a more realistic contact state of the tire can be analyzed.

  The imaging device 10 includes a camera 15 that is an imaging unit that captures an image of the test tire 60 and an illumination lamp 16 that is a light source. The camera 15 is configured by, for example, a CCD (Charge Coupled Device) camera. The camera 15 captures an image of the test tire 60 via the transparent plate 11, thereby capturing an image of the contact surface 61 of the test tire 60 pressed against the transparent plate 11. More specifically, the camera 15 is disposed on the lower surface 11D side, which is the other main surface of the transparent plate 11, so that the optical axis is orthogonal to the lower surface 11D side, and a test is performed from the lower surface 11D side via the transparent plate 11. The tire 60 is photographed. Thereby, the camera 15 captures an image of the test tire 60 including at least the contact surface 61 and generates digital image data of the test tire 60 including the contact surface 61.

  The illumination lamp 16 is a lamp that illuminates the shooting range of the camera 15, and is configured by, for example, a halogen lamp. A plurality of the illumination lamps 16 are provided, and the grounding surface 61 of the test tire 60 pressed against the transparent plate 11 is placed on the lower surface 11D side of the transparent plate 11 via the transparent plate 11 or the transparent plate 11. Irradiation is performed from between the upper surface 11U side and the test tire 60. The plurality of illumination lamps 16 are respectively provided at positions other than the position where the transparent plate 11 that moves as the test tire 60 is rotated by the support device 3 moves.

  The number of these lighting lamps 16 may be varied according to the conditions of the test performed by the tire testing machine 2. For example, when the groove of the test tire 60 is not chamfered, it is not necessary to irradiate light in consideration of the chamfer, and therefore, the number of the illumination lamps 16 may be relatively small. On the other hand, when the groove of the test tire 60 is chamfered, since the luminance of the chamfered portion and the tread surface need to be greatly different, the number of the illumination lamps 16 is increased and the Irradiation with light is preferred. Further, these illumination lamps 16 may be of a constant lighting type or of a flash lighting type.

  The tire contact surface analysis device 20 is, for example, a PC (Personal Computer) in which a predetermined analysis program is installed, and processes an image of the test tire 60 input from the photographing device 10 to analyze the contact surface 61 of the test tire 60. Perform the following processing. The process of analyzing the contact surface 61 of the test tire 60 includes a process of calculating the contact surface 61 based on the captured image of the test tire 60. The tire contact surface analysis device 20 includes a processing device 30 that performs arithmetic processing such as analysis of the contact surface 61 and saves data, an input unit 21 where an operator performs an input operation to the tire contact surface analysis device 20, and an analysis result. And a display unit 22 for displaying various information. A keyboard or a pointing device such as a mouse is used for the input unit 21, and a display device such as a liquid crystal display is used for the display unit 22. The input unit 21 and the display unit 22 are electrically connected to the processing device 30, so that the tire contact surface analysis device 20 allows the operator to perform an input operation on the input unit 21 while visually recognizing the display unit 22. Has become possible. In addition, the camera 15 is connected to the processing device 30 of the tire contact surface analysis device 20, whereby the tire contact surface analysis device 20 can acquire an image captured by the camera 15.

  The processing device 30 included in the tire contact surface analysis device 20 includes a processing unit 31 having a CPU (Central Processing Unit) and the like, and a storage unit 50 such as a RAM (Random Access Memory). The processing unit 31 and the storage unit 50 configured as described above may be provided in the same housing, may be provided in different housings, or the plurality of storage units 50 may be provided in both forms. It may be provided.

  The processing unit 31 included in the processing device 30 includes a contact surface image acquisition unit 32, a groove extraction unit 34, a contour line emphasized image generation unit 33, a total contact region calculation unit 39, and an actual contact region calculation unit 40. Has functionally. Among these, the contact surface image acquisition unit 32 acquires a contact surface image 80 (see FIG. 4) which is an image of the contact surface 61 of the test tire 60.

  Further, the contour-line-enhanced image generation unit 33 generates a contour-line-enhanced image 83 (see FIG. 8) in which a contour 84 (see FIG. 8) in the image is emphasized by differentiating the luminance of the ground plane image 80. . In addition, the groove extracting unit 34 can extract the groove 65 (see FIG. 30) of the test tire 60 from the contact surface image 80 acquired by the contact surface image acquisition unit 32. Further, the total contact area calculation unit 39 obtains the total contact area 110 (see FIG. 26) from the contact surface image 80. In addition, the actual contact area calculation unit 40 removes the groove 65 extracted by the groove extraction unit 34 from the total contact area 110 calculated by the total contact area calculation unit 39 to determine an actual contact area 111 (see FIG. 31).

  The groove extracting unit 34 includes a scanning line setting unit 35, a luminance comparing unit 36, a determining unit 37, and a groove image generating unit 38. The scanning line setting unit 35 sets the scanning line 70 (see FIG. 14) for the ground plane image 80. In addition, the luminance comparing unit 36 performs scanning when the average luminance in the area where the scanning line 70 is located is defined as the land local luminance, and a value obtained by subtracting a constant value from the land local luminance is determined as the groove local luminance. The luminance of the center pixel 74 of the line 70 (see FIG. 17) is compared with the groove local luminance.

  When the luminance of the center pixel 74 is smaller than the local luminance of the groove, the determination unit 37 generates a luminance differential profile 95 (see FIG. 19) of the ground plane image 80 in the range where the scanning line 70 is located, and A local maximum point having a luminance differential value equal to or larger than a predetermined threshold value is extracted from the differential profile 95, and two points closest to the central pixel 74 on both sides in the length direction of the scanning line 70 sandwiching the central pixel 74 among the local maximum points. Is determined as the groove 65. The groove image generation unit 38 generates a groove image 87 (see FIG. 30) that is an image of the groove 65 extracted from the ground contact surface image 80 by combining the elements determined as the grooves 65 by the determination unit 37.

  The analysis program used in the tire contact surface analysis device 20 is stored in the storage unit 50 in advance, and when analyzing the contact surface 61 of the test tire 60, the program stored in the storage unit 50 is processed by the processing unit. Each function is executed by calling at 31 and executing the operation according to the program at the processing unit 31.

  The tire contact surface analysis system 1 and the tire contact surface analysis device 20 according to the present embodiment are configured as described above, and the operation thereof will be described below. When the contact surface 61 of the test tire 60 is analyzed by the tire contact surface analysis system 1, the test tire 60 is mounted on the support device 3 of the tire testing machine 2, and the test tire 60 is pressed against the transparent plate 11. While rotating or stopped, the camera 15 captures an image of the ground contact surface 61. At this time, the test tire 60 is photographed in a state where it is irradiated with light from a plurality of illumination lamps 16 from a plurality of directions. For this reason, the camera 15 can photograph the test tire 60 with a difference in luminance between the contact surface 61 and a portion other than the contact surface 61. The photographed image is acquired by the tire contact surface analysis device 20, and the tire contact surface analysis device 20 analyzes the contact surface 61 based on the acquired image.

  Next, a processing procedure when the tire contact surface analysis device 20 analyzes the contact surface 61 will be described. FIG. 3 is a flowchart showing a processing procedure when analyzing the contact surface with the tire contact surface analysis device according to the embodiment. FIG. 4 is an explanatory diagram of a ground contact surface image. When analyzing the contact surface 61 with the tire contact surface analysis device 20, first, a contact surface image 80 which is an image of the contact surface 61 of the test tire 60 is obtained (step ST11). In the present embodiment, as an example of the ground contact surface image 80 of the test tire 60, a case where a so-called studless tire mainly used in winter is used as the test tire 60 will be described. The camera 15 photographs the test tire 60 pressed against the transparent plate 11 through the transparent plate 11, and obtains the image photographed by the camera 15 with the tire contact surface analysis device 20, thereby converting the photographed image. It is acquired as the ground plane image 80. The acquisition of the contact surface image 80 is performed by the contact surface image acquisition unit 32 included in the processing unit 31 of the processing device 30.

  Since the contact surface image 80 acquired by the contact surface image acquisition unit 32 is obtained by simply photographing the test tire 60 from the contact surface 61 side, the contact surface image 80 includes an area other than the contact surface 61 in the test tire 60. ing. The contact surface image 80 is acquired by the contact surface image acquiring unit 32 as an image whose luminance is represented by 256 gradations, for example. In the case where the contact surface 61 is photographed while rotating the test tire 60, the contact surface image acquisition unit 32 transmits the acquired contact surface image 80 to the storage unit 50, and stores the acquired contact surface image 80 one by one.

  Next, noise removal processing is performed on the ground plane image 80 by the ground plane image acquisition unit 32 (step ST12). In other words, the ground contact surface image 80 may include thermal noise from the camera 15 and small dust on the tire surface, which may adversely affect the analysis. Remove noise. FIG. 5 is an explanatory diagram of the ground contact surface image on which the noise removal processing has been performed. The noise elimination process removes so-called sesame salt noise, which is noise generated by being scattered like dots, from the ground contact surface image 80 as shown in FIG. 5 by performing a noise elimination process using a median filter, for example. I do.

  FIG. 6 is an explanatory diagram of a median filter. The median filter used for the noise removal processing will be described. In the processing using the median filter, the target pixel 100 and the peripheral pixels 101 arranged around the target pixel 100 are rearranged in descending order of luminance, and the rearranged luminance Is replaced with the luminance value of the pixel of interest 100. For example, in the case where the luminance of the target pixel 100 and the peripheral pixel 101 are as shown in the numerical values of FIG. 6, when rearranged in descending order of luminance, 243, 171, 102, 80, 79, 50, 40, 10, 1 It becomes order of. In this case, since the intermediate value of the rearranged luminance is 79, the luminance of the target pixel 100 is replaced with 79.

  Note that the noise removal processing of the ground plane image 80 may be performed using a device other than the median filter, for example, using an averaging filter or a Gaussian filter. The averaging filter is a filter process that blurs the entire image by averaging luminance values in a predetermined range. For example, if the luminance of the target pixel 100 and the peripheral pixels 101 is as shown in the numerical values shown in FIG. Replace with

  Further, the Gaussian filter is a filter process that takes in the luminance of the target pixel 100 and the peripheral pixels 101 and obtains a weighted average. FIG. 7 is an explanatory diagram of weights used in the Gaussian filter. Since the Gaussian filter performs weighting according to the distance in consideration of the distance between the target pixel 100 and the peripheral pixel 101, the weight used in the Gaussian filter is the highest for the target pixel 100 as shown in FIG. The larger the peripheral pixel 101 is, the larger the distance from the pixel of interest 100 is. As the luminance of the target pixel 100, a value obtained by multiplying the luminance of the pixel by the weight and averaging is used. For example, when the luminance of the target pixel 100 and the luminance of the peripheral pixel 101 are as shown in the numerical values shown in FIG. 6, when weighted and averaged as shown in FIG. 7, ｛(80 × 1/16) + ( 10 × 2/16) + (50 × 1/16) + (243 × 2/16) + (1 × 4/16) + (102 × 2/16) + (79 × 1/16) + (171 × Since (2/16) + (40 × 1/16)｝ ≒ 82, the luminance of the pixel of interest 100 is replaced with 82.

  In addition, in the description of the noise removal processing using FIGS. 6 and 7, the case where the filter processing is performed in a range of 3 × 3 pixels centering on the target pixel 100 has been described. On the other hand, it is preferable to perform the filter processing over a wider range. For example, it is preferable to perform the filter processing using luminance information in a 9 × 9 range.

  Next, an outline emphasized image 83 is generated from the ground plane image 80 after the noise removal processing (step ST13). FIG. 8 is an explanatory diagram of a contour line emphasized image. The contour-line-enhanced image 83 is obtained by differentiating the luminance of the ground plane image 80 after the noise removal processing by the contour-line-enhanced image generation unit 33 and obtaining the absolute value of the luminance differentiation. An outline emphasized image 83 to be emphasized as 84 is generated. The outline emphasized image 83 is generated using, for example, a Sobel filter.

  FIG. 9 is an explanatory diagram of a Sobel filter when weighting pixels in the vertical direction. FIG. 10 is an explanatory diagram of a Sobel filter when weighting pixels in the horizontal direction. The Sobel filter is a filter process that takes in the luminance of the target pixel 100 and the peripheral pixel 101 and performs weighting calculation. By calculating the luminance with different weights in a plurality of directions, the Sobel filter performs calculation in a plurality of directions. That is, the luminance change rate can be calculated in each of the vertical direction and the horizontal direction of the image. For this reason, the filter used in the Sobel filter is, for example, a filter for performing weighting when calculating in the vertical direction with respect to a pixel as shown in FIG. And a filter for performing weighting when calculating the value.

  FIG. 11 is an explanatory diagram in the case where the absolute value of the luminance derivative is calculated using the filter shown in FIG. For example, in the case where the luminance of the target pixel 100 and the peripheral pixel 101 is as shown in the numerical value shown in the left side of FIG. 11, when the weights shown in FIG. 9 are multiplied, 104 × 1 + 105 × 2 + 97 × 1 + 101 × 0 + 101 × 0 + 96 × 0 + 114 × (−1) + 117 × (−2) + 111 × (−1) = − 48. The brightness (−48) calculated using the filter that weights in the vertical direction in this way is defined as A.

  FIG. 12 is an explanatory diagram in the case where the absolute value of the luminance derivative is calculated using the filter shown in FIG. When the luminance values of the same pixel are weighted as shown in FIG. 10, 104 × 1 + 105 × 0 + 97 × (−1) + 101 × 2 + 101 × 0 + 96 × (−2) + 114 × 1 + 117 × 0 + 111 × (−1) = 20. Let B be the luminance (20) calculated using the filter that weights in the horizontal direction in this way.

The absolute value of the luminance derivative is calculated using the following equation (1) with respect to the value calculated using the Sobel filter as described above. In equation (1), sqrt is a square root in parentheses.
Brightness differential (absolute value) = sqrt (A ² + B ² ) (1)

  By substituting A = −48 and B = 20 into equation (1), the absolute value of the luminance derivative becomes 52. Therefore, the target pixel 100 shown in FIG. 11 and FIG. In the embodiment, since the luminance of the image is represented by 256 gradations, when the calculated absolute value of the luminance derivative is 256 or more, the luminance of the pixel of interest 100 is replaced with 255.

  The contour-line-enhanced image generation unit 33 generates the contour-line-enhanced image 83 by calculating the absolute value of the luminance differentiation for each of the pixels constituting the ground plane image 80 with the pixel of interest 100, and replacing the luminance. . The contour-line emphasized image 83 has a brightness change in a portion where the brightness is changed in the ground contact surface image 80, and as a result, the contour line 84 in the image is emphasized. Has become. The generated outline emphasized image 83 is stored in the storage unit 50 of the processing device 30 separately from the ground contact surface image 80.

  After generating the outline emphasized image 83, the groove 65 is extracted (step ST14). The groove 65 in this case is defined as a groove 65 that is recessed from the tire plane in the tread portion of the test tire 60. The groove 65 includes a lug groove 66 extending in the tire width direction and a main groove 67 extending in the tire circumferential direction. The extraction of these grooves 65 from the ground contact surface image 80 is performed by the groove extraction unit 34 included in the processing unit 31 of the processing device 30.

  FIG. 13 is a flowchart showing the processing procedure for extracting a groove. FIG. 14 is an explanatory diagram of a scanning line. When the groove extraction unit 34 extracts the groove 65 from the ground plane image 80, first, the scanning line 70 is set for the ground plane image 80 after the noise removal processing (step ST21). This setting is performed by the scanning line setting unit 35 included in the groove extracting unit 34. As the scanning line 70, a circumferential scanning line 71 extending in the tire circumferential direction and scanning in the tire circumferential direction, and a width scanning line 72 extending in the tire width direction and scanning in the tire width direction (see FIGS. 24A to 24E) There is. Among them, the circumferential scanning line 71 can extract the lag groove 66, and the width scanning line 72 can extract the main groove 67.

  The length of each of the circumferential scanning line 71 and the width scanning line 72 is at least twice as long as the maximum groove width of the groove 65 to be extracted. It has a width of one pixel. The groove width in this case is the width of the groove 65 with respect to the direction in which the scanning line 70 extends, and regardless of the inclination angle of the groove 65 in the tire circumferential direction or the tire width direction, the width of the lug groove 66 in the tire circumferential direction. And the width of the main groove 67 in the tire width direction. In other words, when the length of the scanning line 70 is less than twice the maximum groove width of the groove 65 to be extracted, the scanning line 70 must not pass through both edges in the groove width direction forming the opening of the groove 65. There is a possibility that the extraction of the groove 65 by the method according to the present embodiment becomes difficult. For this reason, in the present embodiment, the scanning line 70 has a length that is at least twice the maximum groove width of the groove 65 extracted using the scanning line 70. The extraction of the lag groove 66 using the circumferential scanning line 71 and the extraction of the main groove 67 using the width scanning line 72 are performed by the same method. However, in the following description, the scanning line 70 is used. The method of extracting the groove 65 will be described using the circumferential scanning line 71 as a representative.

  The circumferential scanning line 71 is set in a direction extending along the tire circumferential direction of the test tire 60 in the contact surface image 80 with respect to the contact surface image 80. The length is longer than the groove width of the lug groove 66. For example, in the case where the ground contact surface image 80 is an image composed of 1200 vertical pixels × 1600 horizontal pixels, the length of the circumferential scanning line 71 is long. The length is set at about 150 pixels. Since the width of the circumferential scanning line 71 is one pixel, the circumferential scanning line 71 extends as long as 150 pixels in the tire circumferential direction and forms a scanning line 70 having a width of one pixel in the tire width direction. This is set for the ground image 80.

  The scanning line 70 scans while moving on the image in one direction, and after moving from one end to the other end of the image, moves to an adjacent row and repeats scanning while moving in one direction again, so-called, Perform a raster scan. Therefore, when the groove 65 is extracted by the scanning line 70, the scanning line 70 is extracted while scanning near the corner of the image as a scanning start position. Therefore, when the scan line 70 is set by the scan line setting unit 35, the scan line 70 is actually set near one corner in the ground contact surface image 80, but a method of extracting the groove 65 using the scan line 70 will be described. Therefore, in the following description, a case where the scanning line 70 is set on the groove 65 will be described.

  When the scanning line 70 is set in the ground contact surface image 80, the groove 65 is extracted using the scanning line 70 (step ST22). FIG. 15 is a flowchart illustrating a processing procedure for performing the groove extraction processing. FIG. 16 is a detailed view of a portion A in FIG. When performing the process of extracting the groove 65 on the ground contact surface image 80, first, a luminance calculation line 76 is set (step ST31). The luminance calculation line 76 is a line for calculating the land local luminance. The land local luminance is the average luminance in the scanning line 70 and the area in the vicinity thereof, that is, the average luminance in the area where the scanning line 70 is located, and the average luminance of the land 68 in the area where the scanning line 70 is located. Has become. The luminance calculation line 76 is set to have the same length as the length of the scanning line 70, and is shifted by one pixel from the scanning line 70 with respect to the scanning line 70 at each of both sides in the width direction of the scanning line 70. Set to position. That is, two luminance calculation lines 76 are set on each side of the scanning line 70 in the width direction, and a total of four lines are set. Accordingly, in the circumferential scanning line 71, two luminance calculation lines 76 are set on one side of the circumferential scanning line 71 in the tire width direction, and a total of four luminance calculation lines 76 are provided on both sides of the circumferential scanning line 71 in the tire width direction. Set. The area where the four luminance calculation lines 76 set on both sides in the width direction of the scanning line 70 are located is an area 77 near the scanning line 70. In addition, although the luminance calculation lines 76 are set to two lines on each side of the scanning line 70, that is, four in total, the luminance calculation lines 76 may be set to other numbers.

  Next, the determination unit 37 determines whether or not there is a scanning line 70 and a luminance calculation line 76 that are off the ground plane image 80 (step ST32). If it is determined that there is a scan line 70 or a luminance calculation line 76 that protrudes from the contact surface image 80 (step ST32, Yes determination), the process exits from the flow of the groove 65 extraction process. That is, when the scanning line 70 or the brightness calculation line 76 is protruding from the ground plane image 80, the extraction processing of the groove 65 is not performed at the current position of the scanning line 70.

  On the other hand, when it is determined that there is no scanning line 70 and no luminance calculation line 76 that protrude from the ground contact surface image 80 (step ST32, No determination), the land local luminance is calculated (step ST33). The land part local luminance is an area where the scanning line 70 is located on the ground plane image 80, and uses luminance information of a pixel located in a luminance calculation area 78 which is an area composed of the scanning line 70 and the neighboring area 77. calculate. That is, the average value of the pixels located in the luminance calculation area 78 is calculated, and the average value is set as the land-local luminance.

  In addition, since the land local luminance is the local luminance of the land 68, when calculating the land local luminance, the pixel corresponding to the groove 65 on the ground contact surface image 80 is excluded. Is preferred. Specifically, since the pixel corresponding to the groove 65 has low luminance, the pixel corresponding to the groove 65 is excluded by excluding the pixel whose luminance is lower than a predetermined threshold, and is excluded from the calculation of the average luminance. For example, when the luminance is represented by 256 gradations, the low luminance pixels having a luminance of 40 or less are excluded from the calculation of the average luminance, and the pixels corresponding to the grooves 65 are excluded from the calculation of the average luminance. exclude.

  In addition, since the luminance of the non-ground area 82 (see FIG. 14) is significantly different from the luminance of the ground area 81, when calculating the land-local luminance, pixels corresponding to the non-ground area 82 are also excluded. Preferably, the average brightness is calculated. Specifically, since the pixels corresponding to the non-grounded area 82 have higher luminance than the pixels corresponding to the grounded area 81 (see FIG. 14), pixels having a luminance higher than a predetermined threshold are excluded. , The pixel corresponding to the non-ground area 82 is excluded from the calculation of the average luminance. For example, when the luminance is represented by 256 gradations, the high luminance pixels having a luminance of 100 or more are excluded from the calculation of the average luminance, so that the pixels corresponding to the non-ground area 82 are excluded and the average luminance is calculated. Exclude from calculation.

  After the land local luminance is calculated, it is determined whether the luminance of the center pixel 74 of the scanning line 70 is smaller than the groove local luminance (step ST34). FIG. 17 is an explanatory diagram of the center pixel. The center pixel 74 of the scanning line 70 is a pixel located at the center in the length direction of the scanning line 70. In the circumferential scanning line 71, a pixel located at the center of the circumferential scanning line 71 in the tire circumferential direction. It has become. Further, the groove local luminance is obtained by subtracting a fixed value from the land local luminance, and when the luminance is represented by 256 gradations, for example, 40 is subtracted from the land local luminance. Let the luminance be the groove local luminance at the current position of the scan line 70.

  The groove extracting unit 34 extracts the luminance of the central pixel 74 of the scanning line 70, and the luminance comparing unit 36 compares the luminance of the central pixel 74 with the local luminance of the groove. As a result of the comparison, when it is determined that the luminance of the center pixel 74 of the scanning line 70 is not smaller than the local luminance of the groove (step ST34, No determination), the process exits the flow of the groove 65 extraction processing. That is, when the luminance of the center pixel 74 is not smaller than the groove local luminance, it can be determined that the center pixel 74 at the current position of the scanning line 70 is not at the position corresponding to the groove 65, and thus the current scanning line At the position 70, the extraction processing of the groove 65 is not performed.

  On the other hand, when it is determined that the luminance of the central pixel 74 of the scanning line 70 is smaller than the groove local luminance (step ST34, Yes determination), the central pixel 74 is set as a component of the groove 65 in the storage unit. At step ST35, a luminance differential profile is generated (step ST35). FIG. 18 is a detailed view of the contour-line emphasized image at the same position as the ground contact surface image shown in FIG. FIG. 19 is an explanatory diagram of a luminance differential profile. The luminance differential profile 95 is generated by using the outline emphasized image 83. When generating the luminance differential profile 95, first, the scanning line on the ground plane image 80 when the luminance of the center pixel 74 of the scanning line 70 is determined to be smaller than the groove local luminance in the ground plane image 80 A luminance differential scanning line 90 is set at a position on the outline emphasized image 83 corresponding to the position 70.

  This luminance differential scanning line 90 is a line for detecting the absolute value of the luminance differentiation in the outline emphasized image 83 in order to generate a luminance differentiation profile 95, and has the same length as the scanning line 70, This is set for the line emphasized image 83. That is, the luminance differential scanning line 90 is set for the contour-line emphasized image 83 so as to have the same positional relationship as the positional relationship between the ground plane image 80 and the scanning line 70. When the luminance differential scanning line 90 is set for the outline emphasized image 83, the absolute value of the luminance differentiation of the pixel located on the luminance differential scanning line 90 is extracted from the contour emphasized image 83, and By associating the position with the absolute value of the luminance derivative, a luminance derivative profile 95 is generated. As a result, a luminance differential profile 95 that is a profile representing the luminance differential of the ground contact surface image 80 in the range where the scanning line 70 is located is generated.

  Next, a maximum point 96 is extracted from the luminance derivative profile 95 (step ST36). When the maximum point 96 is extracted, a predetermined threshold value is set, and the maximum point 96 having a luminance differential value equal to or higher than the predetermined threshold value is extracted from the luminance differential profile 95. The threshold value in this case is a maximum point cut line 97 set so as to exclude a maximum point 96 having a luminance differential value of a low luminance area corresponding to the groove 65. For example, the ground plane image 80 Is set to a value not less than 1.25 times and not more than 2.5 times the average luminance differential in the total ground area 110 included in. This maximum point cut line 97 is also calculated using the contour emphasized image 83 in the same manner as the luminance differential profile 95, and corresponds to the total ground contact area 110 included in the contact surface image 80, and the total ground contact in the contour emphasized image 83. The maximum point cut line 97 is set at a value of 1.25 times or more and 2.5 times or less of the average luminance derivative in the area 110.

In other words, when the extracted maximum point 96 is represented using a coefficient α that satisfies (1.25 ≦ α ≦ 2.5), the absolute value of the luminance derivative of each maximum point 96 is expressed by the following equation (2). ) Are extracted.
Absolute value of luminance derivative of local maximum point 96 ≧ α × Absolute value of average luminance derivative in total contact area 110 (2)

  Next, a range GW sandwiched between the two maximum points 96 closest to the center pixel 74 is determined as the groove 65 (step ST37). That is, the determination unit 37 determines the center pixel in the length direction of the scan line 70 sandwiching the center pixel 74, that is, on both sides in the length direction of the luminance differential scan line 90, among the plurality of extracted maximum points 96. An area GW sandwiched between the two maximum points PC and PD closest to 74 is determined as the groove 65. In this case, the contour line emphasized image 83 is surrounded by the two maximum points PC and PD, and corresponds to the pixel group arranged in one line in the tire circumferential direction. The pixel group is stored in the storage unit 50 as a component of the groove 65. That is, a pixel group on the ground plane image 80 at the same position as the pixel group sandwiched between the two maximum points PC and PD in the outline emphasized image 83 is stored in the storage unit 50 as a component of the groove 65. .

  Here, the pneumatic tire may be provided with a stamp 63 (see FIG. 4) applied to the tread surface at the time of manufacture, a marking or the like written at the time of the test. In many cases, the brightness of the marked portion is different from that of the portion without the mark 63 or the like. For this reason, when extracting the groove 65 based on the luminance, there is a possibility that the groove 65 may not be properly extracted in the portion where the mark 63 is provided. However, in the present embodiment, the luminance is differentiated. Accordingly, the local maximum points PC and PD having a large degree of change in luminance can be extracted from the luminance differential profile 95 at the positions on both sides of the center pixel 74 determined to be the positions corresponding to the grooves 65. The groove 65 provided in the portion where the inscription 63, which tends to have a different luminance from that of the mark 63, can be appropriately extracted.

  Further, in the present embodiment, it is possible to appropriately extract the groove 65 in a portion where the engraving 63 is not provided. FIG. 20 is an explanatory diagram showing a state where a scanning line is located at a portion where no marking is given. Even when the scanning line 70 is located at a position where the engraving 63 is not applied, when it is determined that the luminance of the central pixel 74 of the scanning line 70 is smaller than the groove local luminance (step ST34, Yes determination), The center pixel 74 is stored in the storage unit 50 as a component of the groove 65, and a luminance differential profile 95 is generated (step ST35). That is, regardless of the position of the scanning line 70, when it is determined that the luminance of the center pixel 74 is smaller than the groove local luminance, the luminance differential profile 95 is generated.

  FIG. 21 is a detailed view of the contour line emphasized image at the same position as the ground contact surface image shown in FIG. FIG. 22 is an explanatory diagram of a luminance differential profile. The luminance differential profile 95 is a contour corresponding to the position of the scanning line 70 on the ground plane image 80 when the luminance of the central pixel 74 of the scanning line 70 is determined to be smaller than the groove local luminance in the ground plane image 80. A luminance differential scanning line 90 is set at a position on the line emphasized image 83 and generated. When the luminance differential profile 95 is generated, the local maximum point 96 is extracted by setting the local maximum point cut line 97 (step ST36). However, at the position where the engraving 63 is not applied, the change in the luminance of the land portion 68 becomes small. ing.

  For this reason, the luminance differential value is small except for the edge portion in the width direction of the groove 65, and a portion corresponding to two edge portions in the width direction of the groove 65 appears as a maximum point 96. The determination unit 37 determines, as the groove 65, a range GW sandwiched between the two maximum points 96 closest to the center pixel 74, and thus the pixel sandwiched between the two maximum points PC and PD in the outline emphasized image 83. The pixel group on the ground plane image 80 at the same position as the group is stored in the storage unit 50 as a component of the groove 65. Thus, the groove 65 can be extracted even at a position where the stamp 63 is not provided.

  When the extraction processing of the groove 65 at one position is completed using the contour emphasized image 83 and the luminance differential scanning line 90, the process returns to the processing on the ground contact surface image 80, and is the position of the scanning line 70 the end position? It is determined whether or not it is (step ST23). That is, since the scan line 70 performs the raster scan, it is determined whether or not the current position of the scan line 70 is the end position.

  FIG. 23A to FIG. 23E are explanatory diagrams of how a scanning line advances. The manner in which the scanning line 70 advances when scanning is performed using the scanning line 70 will be described with reference to the circumferential scanning line 71. In step ST21, the circumferential scanning line 71 is located at, for example, the upper leftmost position of the ground plane image 80. Is set so as to extend in the left-right direction (FIG. 23A). When the groove 65 is extracted at this position, the circumferential scanning line 71 is moved one pixel to the right (FIG. 23B), and by repeating these, the circumferential scanning is performed while extracting the groove 65 at each position. The line 71 is moved rightward.

  Thereby, when the circumferential scanning line 71 moves to the right end of the ground plane image 80 (FIG. 23C), the circumferential scanning line 71 is moved to the left end of the next lower row of pixels. (FIG. 23D). In this manner, the circumferential scanning line 71 is sequentially moved to the right by one pixel at a time, and after moving to the right end, the circumferential scanning line 71 is repeatedly moved to the left end of the next lower row of pixels. It is moved to the lower rightmost part of the contact surface image 80 (FIG. 23E). This position is the end position when the circumferential scanning line 71 is moved while extracting the groove 65.

  After the process of extracting the groove 65 at the current position of the scan line 70 is completed, it is determined whether or not the position of the scan line 70 is the end position (step ST23), and the position of the scan line 70 is not the end position. Is determined (step ST23, No determination), the scanning line 70 is moved (step ST24). In this case, the scanning line 70 is moved from the current position by one pixel in the length direction of the scanning line 70 or to the position of the end of the adjacent row. After moving the scanning line 70, the process returns to step ST22, and the groove 65 is extracted again. By repeating these steps, the groove 65 is extracted in the entire area of the ground contact surface image 80.

  In the above description, the case where the lug grooves 66 are extracted using the circumferential scanning lines 71 has been described. However, the case where the main grooves 67 are extracted using the width scanning lines 72 is also performed in the same manner. . That is, when it is determined that the luminance of the center pixel 74 at the current position of the width direction scanning line 72 is smaller than the groove local luminance, both sides in the length direction of the scanning line 70 across the center pixel 74 , The two maximum points PC and PD closest to the center pixel 74 are obtained, and the components of the main groove 67 are extracted.

  Further, since the width direction scanning line 72 is set in a direction extending along the tire width direction of the test tire 60 and is provided in a direction orthogonal to the circumferential direction scanning line 71, the moving direction is also the circumferential direction scanning line 71. Is a direction orthogonal to the moving direction of FIG. 24A to FIG. 24E are explanatory diagrams of how to advance the scanning line in the width direction. In step ST21, for example, the width direction scanning line 72 is set to extend in the vertical direction at the uppermost left portion of the ground contact surface image 80 (FIG. 24A). After the main groove 67 is extracted at this position, the width direction scanning line 72 is moved downward by one pixel (FIG. 24B), and by repeating these, the width of the main groove 67 is extracted at each position. The direction scanning line 72 is moved downward.

  As a result, when the width direction scanning line 72 moves to the lower end of the ground plane image 80 (FIG. 24C), the width direction scanning line 72 is moved to the upper end of the right column of the pixel (FIG. 24C). (FIG. 24D). As described above, the width direction scanning line 72 is sequentially moved downward by one pixel at a time, and after moving to the lower end, the width direction scanning line 72 is repeatedly moved to the upper end of the one right column of the pixels, so that the width direction scanning line 72 is connected. The ground image 80 is moved to the lowermost position (FIG. 24E). This position is the end position when the width direction scanning line 72 is moved while extracting the main groove 67.

  Also in the width direction scanning line 72, after the main groove 67 extraction processing at the current width direction scanning line 72 position is completed, it is determined whether or not the position of the width direction scanning line 72 is the end position (step S1). In ST23), when it is determined that the position of the width direction scanning line 72 is not the end position (step ST23, No determination), the width direction scanning line 72 is moved (step ST24). In this case, the pixel is moved from the current position of the width direction scanning line 72 by one pixel in the length direction of the width direction scanning line 72 or to the position of the end of the adjacent row. After moving the scanning line 72 in the width direction, the process returns to step ST22, and the main groove 67 is extracted again. By repeating these, the extraction processing of the main groove 67 is performed in the entire region of the ground contact surface image 80.

  When it is determined that the position of the scanning line 70 is the end position in both the circumferential scanning line 71 and the width scanning line 72 (step ST23, Yes determination), the groove is formed in the entire area of the ground contact surface image 80. Since the extraction processing of 65 has been performed, the processing exits from the processing of extracting the groove 65.

  When the extraction of the groove 65 is completed, next, the total contact area 110 is obtained (step ST15). FIG. 25 is an explanatory diagram of the ground area image generated based on the luminance. FIG. 26 is an explanatory diagram of the total contact area image. When obtaining the total contact area 110, first, the contact area image 85 is generated from the contact surface image 80 by the total contact area calculation unit 39. When the contact area image 85 is generated, the contact area image 85 is generated by performing a binarization process on the contact surface image 80. That is, in the ground contact surface image 80, since the luminance is different between the groove 65 and the land portion 68, binarization is performed using the luminance with a threshold value at which the groove 65 and the land portion 68 can be separated. Thereby, for example, the ground area image 85 in which the groove 65 is a white pixel and the land portion 68 is a black pixel and the ground area 81 is represented is generated.

  Further, in the contact area image 85, the main groove 67 located in the non-contact area 82 is excluded. When the main groove 67 located in the non-ground area 82 is obtained, for example, a contour image in which the contour in the ground area image 85 is extracted from the ground area image 85 using a Sobel filter or the like is used. In the non-ground area 82 of the contour image, the total number of black pixels in the tire circumferential direction is extracted for each position in the tire width direction. From the extracted total number of black pixels at each position in the tire width direction, the position of the edge of the main groove 67 in the tire width direction is extracted, and the position of the main groove 67 is extracted. The main groove 67 is presumed to be located over the entire area in the tire circumferential direction of the ground area image 85, and thus the black pixels on the ground area image 85 located at the position of the main groove 67 extracted in this way are white pixels. , The main groove 67 located in the non-ground area 82 in the ground area image 85 is excluded.

  After the main groove 67 located in the non-ground area 82 is excluded on the ground area image 85, the expansion processing and the contraction processing are repeated on the ground area image 85, so that white pixels are formed in the ground area image 85. The indicated groove 65 is removed. FIG. 27 is an explanatory diagram of the expansion processing. FIG. 28 is an explanatory diagram of the contraction processing. As shown in FIG. 27, the expansion process is a process of replacing the target pixel with a black pixel if there is at least one black pixel around the target pixel. That is, the expansion process is performed by setting each white pixel as a center pixel and one of the eight surrounding pixels (one pixel at the upper left, upper, upper right, right, lower right, lower, lower left, and lower left nearest to the center pixel) However, if a black pixel exists, the center pixel is replaced with a black pixel. Conversely, in the contraction process, for example, when the target pixel is a black pixel, as shown in FIG. 28, if at least one white pixel exists around the target pixel, the target pixel is replaced with a white pixel. . In other words, the contraction processing is performed by setting each of the black pixels as the center pixel and one of the eight surrounding pixels (one pixel at the upper left, upper, upper right, right, lower right, lower, lower left, and lower left nearest to the center pixel). However, if a white pixel exists, the center pixel is replaced with a white pixel.

  In the present embodiment, in order to remove a portion corresponding to the groove 65 in the ground area image 85, first, a white pixel is replaced with a black pixel by performing expansion processing a plurality of times, and a portion of the groove 65 in the ground area 81 is removed. I do. After that, in order to return the size of the contact area 81, which has been increased by performing the expansion processing, to the original size, the contraction processing is performed the same number of times as the expansion processing. The total contact area calculation unit 39 performs, for example, the expansion processing 80 times on the contact area image 85, and then performs the contraction processing 80 times, thereby removing the groove 65 portion in the contact area 81 of the contact area image 85. Then, an image of the total contact area 110 that is the obtained image is generated, and the total contact area image 86 is obtained. Thus, the total ground area 110 is obtained.

  FIG. 29 is an explanatory diagram of a groove image. After obtaining the total contact area 110, a groove image 87 is generated (step ST16). The generation of the groove image 87 is performed by the groove image generation unit 38 included in the groove extraction unit 34. The groove image generating unit 38 extracts using the circumferential scanning lines 71, extracts the components of the lug grooves 66 stored in the storage unit 50, and extracts using the width scanning lines 72, and stores them in the storage unit 50. By composing all the components of the main groove 67 as black pixels, one groove image 87 is generated as an image of the entire groove 65 included in the ground contact surface image 80. That is, in step ST37, the area sandwiched by the local maximum points PC and PD closest to the center pixel 74 is determined as the groove 65, and the pixel group in this boundary area is stored in the storage unit 50 as a component of the groove 65. By connecting the constituent elements of the groove 65 thus formed by the groove image generation unit 38, a groove image 87 of the entire groove 65 included in the ground contact surface image 80 can be obtained.

  Further, for the groove image 87, the main groove 67 located in the non-ground region 82, which is excluded in the ground region image 85, is excluded. Accordingly, it is possible to generate a groove image 87 that displays only the groove 65 located in the contact area 81 of the contact area image 85.

  In addition, when the groove image 87 is generated, the isolated point 121 which is a small lump of black pixels on the groove image 87 is removed by repeating the contraction processing and the expansion processing, and the groove 65 displayed by the black pixel is formed. The hole-like portion 122 which appears in a hole shape at the portion is removed, or the separation portion 123 where the lug groove 66 to be connected and the main groove 67 are separated is connected. As a result, when the groove 65 is extracted, a portion other than the groove 65 is extracted as a component of the groove 65 or a portion of the groove 65 is not extracted as a component of the groove 65 due to uneven brightness or the like. The troubles that occur can be eliminated, and the appearance of the groove 65 can be improved.

  FIG. 30 is an explanatory diagram of the groove image after performing the contraction processing and the expansion processing. In the present embodiment, in order to eliminate these problems of the groove image 87, the contraction processing is performed once, and then the expansion processing is performed seven times. Thereafter, the contraction process is performed eight times, and the expansion process is performed twice. Thereby, a good-looking groove image 87 can be obtained. The number and order of these contraction processing and expansion processing, and the number of continuous black pixels as a reference when removing a lump of black pixels are determined by the tread pattern of the test tire 60, the test conditions, and the resolution of the image. It is preferable to set appropriately according to the conditions.

  Next, the actual ground area 111 is obtained (step ST17). FIG. 31 is an explanatory diagram of the actual ground area image. The actual contact area 111 is obtained by removing the groove 65 extracted by the groove extracting section 34 from the total contact area 110 obtained by the total contact area calculation section 39 by the actual contact area calculation section 40. That is, by replacing the portion corresponding to the groove 65 of the ground plane image 80 with a white pixel in the total ground region image 86 of the binary image in which the total ground region 110 is a black pixel, the portion corresponding to the groove 65 is changed. A real ground area image 88 which is an image of the real ground area 111 that has become a white pixel is generated. In the contact area image 85 generated by performing the binarization processing on the contact surface image 80, the mark 63 may also appear in the image, and the mark 63 may be analyzed as the groove 65. After the image 86 and the groove image 87 are generated, by removing a portion corresponding to the groove image 87 from the total contact region image 86, it is possible to obtain an actual contact region image 88 that does not include the mark 63.

  The tire contact surface analysis system 1 acquires a large number of contact surface images 80 with one test tire 60, and extracts the grooves 65 from these contact surface images 80 by the above-described tire contact surface analysis method. In the contact surface image 80, a highly accurate actual contact region image 88 can be easily acquired.

  When the luminance of the center pixel 74 of the scanning line 70 is smaller than the local luminance of the groove, the tire contact surface analysis device 20 according to the above-described embodiment generates the luminance differential profile 95, and generates the groove 65 based on the luminance differential profile 95. Therefore, the groove 65 can be extracted without being affected by the stamp 63 or the like even if the stamp 63 or the like is provided on the tread surface of the test tire 60. FIG. 32 is an explanatory diagram of the luminance at the position of the scanning line shown in FIG. That is, since the change in luminance is large in the portion where the mark 63 or the like is given, when the groove 65 is extracted based on the luminance, if the mark 63 or the like exists at the position to be extracted, the luminance on the scanning line 70 Varies greatly. For this reason, for example, even if the range surrounded by the local maximum points PC and PD shown in FIG. There is a possibility that the range to be extracted may be extracted as a component of the groove 65. On the other hand, in the present embodiment, the groove 65 is not extracted using the luminance as it is, but the groove 65 is extracted using the differential value of the luminance. Therefore, the influence of the stamp 63 or the like at the time of extraction is excluded as much as possible. be able to. As a result, the shape of the groove 65 can be appropriately extracted even when the mark 63 or the like is provided on the tread surface, and the analysis error in analyzing the contact area can be reduced.

  Further, since it is determined whether or not the luminance of the center pixel 74 of the scanning line 70 is smaller than the local luminance of the groove, the groove 65 is extracted based on the luminance differential profile 95, thereby reducing erroneous detection of the groove 65. be able to. FIG. 33 is an explanatory diagram of a scanning line located in a portion where no groove exists. FIG. 34 is an explanatory diagram of the luminance at the position shown in FIG. FIG. 35 is an explanatory diagram of a luminance differential scanning line at a position corresponding to FIG. FIG. 36 is an explanatory diagram of the luminance differential profile at the position shown in FIG. For example, as shown in FIG. 33, when the scanning line 70 located in a portion where the groove 65 does not exist is located, the luminance of the central pixel 74 is higher than the local luminance of the groove. That is, when the groove local luminance is set as the luminance cut line 75 and the scanning line 70 is located in a portion where the groove 65 does not exist, the luminance of the central pixel 74 is higher than the luminance cut line 75. In such a case, when the luminance differential scanning line 90 is set at the same position in the outline emphasized image 83 and the luminance differential profile 95 is generated to extract the local maximum point 96, the local maximum of the two points closest to the central pixel 74 is obtained. Since the area GW surrounded by the points PC and PD is determined as the groove 65, a portion where the groove 65 does not exist is extracted as a component of the groove 65.

  FIG. 37 is an explanatory diagram illustrating a state where the luminance of the center pixel is lower than the luminance cut line. On the other hand, in the present embodiment, the luminance of the central pixel 74 of the scanning line 70 and the luminance cut line 75 are compared by the luminance comparing unit 36, and as shown in FIG. Only when it is lower than the cut line 75, the luminance differential scanning line 90 is set at the same position in the outline emphasized image 83, and the groove 65 is extracted. Thus, it is possible to suppress extraction of a portion where the groove 65 does not exist as a component of the groove 65, and as a result, it is possible to more reliably reduce an analysis error in analyzing the ground contact region.

  Further, as the scanning line 70, a circumferential scanning line 71 set in a direction extending along the tire circumferential direction of the test tire 60, and a width direction scanning line set in a direction extending along the tire width direction of the test tire 60 Since 72 is set, the groove 65 can be extracted using the circumferential scanning line 71 and the width scanning line 72 regardless of the direction of the groove 65 of the test tire 60. Accordingly, even when the groove 65 extending in any direction of the tire circumferential direction and the tire width direction is formed over the stamp 63 or the marking, the groove 65 can be appropriately formed without being affected by the stamp 63 or the like. Can be extracted. As a result, an analysis error in analyzing the ground contact region can be reduced more reliably.

  Further, the scanning line 70 is set to have a length longer than twice the maximum width of the width of the groove 65 intersecting the scanning line 70 in the ground plane image 80 in the length direction of the scanning line 70. The groove 65 can be reliably extracted. In other words, when the length of the scanning line 70 is less than twice the maximum groove width of the groove 65 to be extracted, the scanning line 70 must not pass through both edges in the groove width direction forming the opening of the groove 65. There is. In this case, since the positions of the local maximum points PC and PD corresponding to both edges of the groove 65 cannot be extracted from the luminance differential profile 95, the extraction of the groove 65 may be difficult. On the other hand, in this embodiment, the length of the scanning line 70 is set to be at least twice the maximum groove width of the groove 65 to be extracted. The positions of the local maximum points PC and PD corresponding to the edge can be more reliably extracted. As a result, the shape of the groove 65 can be more reliably extracted, and the analysis error in analyzing the ground contact area can be reduced.

  Further, since the maximum point cut line 97 is 1.25 times or more and 2.5 times or less of the average luminance differential in the total ground contact area 110 included in the ground contact surface image 80, the groove 65 can be extracted more reliably. it can. That is, when the maximum point cut line 97 is less than 1.25 times the average luminance derivative, the maximum point 96 easily exceeds the maximum point cut line 97, so that the maximum point 96 corresponding to the edge of the groove 65 is erroneously recognized. May occur, and analysis accuracy may be reduced. If the maximum point cut line 97 exceeds 2.5 times the average luminance derivative, the maximum point 96 corresponding to the edge of the groove 65 may not be able to exceed the maximum point cut line 97. Cannot be recognized, and there is a possibility that the analysis accuracy is reduced. On the other hand, when the maximum point cut line 97 is set within a range of 1.25 times or more and 2.5 times or less of the average luminance derivative, a candidate of the maximum point 96 corresponding to the edge of the groove 65 is extracted. At this time, since the number of candidates can be appropriately extracted without excessively increasing or narrowing down, the positions of the local maximum points PC and PD corresponding to both edges of the groove 65 can be more appropriately extracted. As a result, the shape of the groove 65 can be more reliably extracted, and the analysis error in analyzing the ground contact area can be reduced.

  In addition, the luminance of the ground contact surface image 80 is differentiated to generate the outline emphasized image 83 in which the outline 84 in the image is emphasized, and the luminance differential profile 95 is generated using the outline emphasized image 83. , The luminance differential profile 95 for extracting the groove 65 without being affected by the stamp 63 or the like can be easily generated. As a result, it is possible to more easily reduce an analysis error in analyzing the ground area.

  Further, the tire ground contact surface analysis system 1 according to the embodiment is configured such that the ground contact surface 61 of the test tire 60 pressed against the transparent plate 11 is illuminated by the plurality of illumination lamps 16, and the camera 15 passes through the transparent plate 11. Thus, the ground plane 61 can be photographed with a luminance difference between the ground plane 61 and the non-ground plane. At this time, since the test tire 60 is photographed in a state where light is emitted from the plurality of illumination lamps 16 from a plurality of directions, the groove 65 and a portion other than the groove 65 are photographed with a difference in luminance. can do. Accordingly, the contour line 84 of the groove 65 can be more reliably emphasized, and the groove 65 can be more reliably extracted from the ground contact surface image 80. As a result, an analysis error in analyzing the ground contact region can be reduced more reliably.

  Further, the tire ground contact surface analysis method according to the embodiment generates the luminance differential profile 95 when the luminance of the center pixel 74 of the scanning line 70 is smaller than the groove local luminance, and creates the groove 65 based on the luminance differential profile 95. For the extraction, even when the tread surface of the test tire 60 is provided with the stamp 63 or the like, the groove 65 can be extracted without being affected by the stamp 63 or the like. As a result, the shape of the groove 65 can be appropriately extracted even when the mark 63 or the like is provided on the tread surface, and the analysis error in analyzing the contact area can be reduced.

(Modification)
In the tire contact surface analysis device 20 according to the above-described embodiment, the local maximum point cut line 97 is set based on the average luminance differentiation in the total ground contact area 110. It may be set using a value other than the average luminance differentiation in the area 110. For example, the absolute value of the average luminance differential in the range of the luminance differential scan line 90 is calculated for each position of the luminance differential scan line 90, and the maximum point cut line 97 is calculated for each position of the luminance differential scan line 90 based on the average luminance differential. May be set. When setting the maximum point cut line 97 from the average luminance derivative in the range of the luminance differential scan line 90, for example, a value of 0.91 to 1.83 times the average luminance derivative in the range of the luminance differential scan line 90 Set with.

The maximum point 96 extracts, from a plurality of profiles of the luminance differential profile 95, those having the luminance differential scanning line 90 or more set in this manner. That is, when the maximum point 96 to be extracted is expressed by using a coefficient β that satisfies (0.91 ≦ β ≦ 1.83), the absolute value of the luminance component of each maximum point 96 is expressed by the following equation (3). Those that satisfy are extracted. In this case, the value of β is such that the value of “β × the absolute value of the average luminance component in the range of the luminance differential scanning line 90” matches the value of “α × the absolute value of the average luminance derivative in the total ground area 110”. Set to
Absolute value of luminance derivative of local maximum point 96 ≧ β × absolute value of average luminance derivative in the range of luminance derivative scan line 90 (3)

  However, when the luminance differential scanning line 90 is out of the total ground area 110, a high luminance differential value is also taken in, and it is difficult to accurately determine the absolute value of the average luminance differential in the luminance differential scanning line 90. For this reason, when the luminance differential scanning line 90 protrudes outside the total ground area 110, it is preferable to set the local maximum point cut line 97 according to the equation (2) without using the equation (3).

  Further, in the above-described embodiment, the case where the studless tire is used as the test tire 60 is described, but the test tire 60 may be other than the studless tire. As the test tire 60, a so-called summer tire used at a time other than winter may be used. FIG. 38 is an explanatory diagram showing a state in which a scanning line is set on a summer tire. FIG. 39 is an explanatory diagram of luminance at the position shown in FIG. FIG. 40 is an explanatory diagram of the luminance differential profile at the position shown in FIG. Even when the test tire 60 is a summer tire, when the groove 65 is detected, a scan line 70 is set for the ground contact surface image 80, and whether the luminance of the center pixel 74 is lower than the luminance cut line 75 is determined. Is determined. If the luminance of the central pixel 74 is lower than the luminance cut line 75 by this determination, a luminance differential profile 95 is generated, and the two maximum points 96 closest to the central pixel 74 are extracted from the groove 65. Are extracted as the maximum points PC and PD. Accordingly, even when the test tire 60 is a summer tire, the groove 65 can be appropriately extracted without being affected by the stamp 63 or the like, and the analysis error in analyzing the ground contact region is reduced. be able to.

REFERENCE SIGNS LIST 1 tire contact surface analysis system 2 tire testing machine 3 support device 5 drive device 10 photographing device 11 transparent plate 15 camera (photographing unit)
16 Lighting lamp (light source)
Reference Signs List 20 tire contact surface analysis device 30 processing device 31 processing unit 32 contact surface image acquisition unit 33 contour emphasized image generation unit 34 groove extraction unit 35 scan line setting unit 36 brightness comparison unit 37 determination unit 38 groove image generation unit 39 total contact area Calculation unit 40 Actual contact area calculation unit 50 Storage unit 60 Test tire (pneumatic tire)
61 ground plane 63 stamp 65 groove 66 lug groove 67 main groove 68 land part 70 scan line 71 circumferential scan line 72 width scan line 74 central pixel 75 luminance cut line 76 luminance calculation line 77 neighborhood area 78 luminance calculation area 80 ground plane Image 81 grounded area 82 non-grounded area 83 contour emphasized image 84 contour 85 grounded area image 86 total grounded area image 87 groove image 88 actual grounded area image 90 luminance differential scanning line 95 luminance differential profile 96 local maximum point 97 local maximum point cut line 110 Total ground area 111 Actual ground area

Claims (8)

A contact surface image acquisition unit that acquires an image of the contact surface of the pneumatic tire,
A groove extraction unit that extracts the groove of the pneumatic tire from the contact surface image acquired by the contact surface image acquisition unit,
With
The groove extraction unit,
A scanning line setting unit that sets a scanning line for the ground plane image,
In the case where the average luminance in the region where the scanning line is located is the land local luminance, and a value obtained by subtracting a certain value from the land local luminance is the groove local luminance, the luminance of the central pixel of the scanning line is obtained. And a brightness comparison unit that compares the groove local brightness,
When the luminance of the center pixel is smaller than the groove local luminance, a luminance differential profile of the ground plane image in a range where the scanning line is located is generated, and a luminance differential value equal to or greater than a predetermined threshold value from the luminance differential profile. Extracting the local maximum point having the maximum point, the region sandwiched by the two local maximum points closest to the central pixel on each of both sides in the length direction of the scan line sandwiching the central pixel among the local maximum points. A determining unit for determining as a groove,
A tire contact surface analysis device, comprising:   The scanning line setting unit is configured to set, as the scanning line, a circumferential scanning line set in a direction extending along a tire circumferential direction of the pneumatic tire and a direction extending along a tire width direction of the pneumatic tire. The tire ground contact surface analysis device according to claim 1, wherein the width direction scanning line to be set is set.   3. The scanning line is set to have a length longer than twice a maximum width of a width in a length direction of the scanning line of the groove intersecting the scanning line in the ground contact surface image. 4. The tire tread analysis device according to 4.   The tire contact surface analysis device according to any one of claims 1 to 3, wherein the threshold value is 1.25 times or more and 2.5 times or less of an average luminance derivative in a total contact region included in the contact surface image. . An outline-emphasized image generation unit that generates an outline-enhanced image in which an outline in the image is emphasized by differentiating the luminance of the ground plane image,
The tire ground contact surface analysis device according to any one of claims 1 to 4, wherein the brightness differential profile is generated using the contour-line-enhanced image. A total contact area calculation unit for determining a total contact area from the contact surface image,
From the total contact area calculated by the total contact area calculation unit, an actual contact area calculation unit that removes the groove extracted by the groove extraction unit to determine an actual contact area,
The tire contact surface analysis device according to any one of claims 1 to 5, further comprising: A tire tread analysis device according to any one of claims 1 to 6,
A transparent plate for pressing the pneumatic tire,
A plurality of light sources that irradiate the ground plane pressed against the transparent plate,
A photographing unit that photographs the ground plane through the transparent plate,
A tire ground contact surface analysis system, comprising: Obtaining an image of the ground plane of the pneumatic tire ;
Setting a scan line relative to contact the ground image,
In the case where the average luminance in the region where the scanning line is located is the land local luminance, and a value obtained by subtracting a certain value from the land local luminance is the groove local luminance, the luminance of the central pixel of the scanning line is obtained. And comparing the groove local brightness with;
When the luminance of the center pixel is smaller than the groove local luminance, a luminance differential profile of the ground plane image in a range where the scanning line is located is generated, and a luminance differential value equal to or greater than a predetermined threshold value from the luminance differential profile. extracts local maximum points with the area sandwiched by the maximum point of the two nearest points to the center pixel in each of the opposite sides in the length direction of the center the scan line across the pixels of the maximum point Determining the groove as a pneumatic tire groove;
A tire ground contact surface analysis method, comprising: