JP2003279845A - Imaging device - Google Patents

Abstract

(57) [Problem] To provide an imaging device having a good balance between accuracy of a focus position and derivation time in the entire driving range of an imaging lens. After obtaining an evaluation value, it is determined whether or not there is a next interpolable section (S204). If there is an interpolable section, interpolation is performed on the interpolable section at every minimum drive interval. A value is given (S205). The way of providing the interpolated value is realized by first obtaining an interpolation function that returns an evaluation value for the drive position at the boundary, and substituting each drive position. As an example, the method of deriving the interpolation function is a method of deriving a cubic natural spline function. The tendency of the interpolated section is checked to determine whether the in-focus position has already been determined (S206). If the in-focus position is known, the image pickup lens is driven to the in-focus position and the process is terminated (S207, S207).
208).

Description

Detailed Description of the Invention

The present invention relates to an image pickup device such as a digital camera, and can be applied to an automatic focusing device and an automatic focusing position detecting method for detecting a focusing position by CCD-AF, for example.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication No. 2000-281529 discloses an efficient focus position determination in view of a problem of a contrast method adopted for performing autofocus in a photographing device such as a video camera. A capable digital camera has been proposed. This is to drive the imaging lens stepwise at an interval larger than the depth of field, obtain an evaluation value based on the captured image obtained from the image sensor at each drive step, and perform a plurality of evaluations at a plurality of drive steps. By performing a predetermined interpolation process on the value, the focusing position of the imaging lens for matching the focusing surface with the imaging surface is derived, and a control unit for driving the imaging lens to the focusing position is provided. It is characterized by having. By the interpolation processing of the evaluation value, both shortening of the focusing position derivation time and maintenance of high accuracy are achieved.

[0003]

However, since the image pickup lens is driven at an interval larger than the depth of field,
Depending on the focal length of the lens and the brightness (F number) of the lens, if the scanning range for automatic focusing is divided at intervals larger than the depth of field, the accuracy of interpolation calculation may not be obtained or interpolation may not be possible. .

FIG. 10A shows a situation of an example of the above problem. In FIG. 10A, the horizontal axis represents the position of the imaging lens based on the reciprocal of the focal length (Lim (∞) is the focal length infinity, Li
m (Nr) is the same closest distance), and the vertical axis represents the focus evaluation value at the position of the imaging lens. This evaluation value has a feature that the intersection of the vertical axis of the horizontal axis passing through the point where the evaluation value is maximum and the horizontal axis is the in-focus position. Figure 11 shows the legend. The case of FIG. 10A is an example of a situation in which the depth of field is as large as 50a, and the number of sampling points is small, so that interpolation accuracy cannot be obtained. Further, as shown in FIG. 10B, when the peak of the evaluation value curve with respect to the focal length of the imaging lens is geometrically asymmetric, it may not be possible to perform highly accurate interpolation. Further, as shown in FIGS. 10 (c) and 10 (d), when the in-focus position is at infinity, at the closest position, or in the vicinity thereof, the application of the steep slope extension method used in the prior art is not possible. No, no interpolation is possible.

The present invention has been made in view of the above problems, and an object thereof is to provide an image pickup apparatus in which the precision of the in-focus position and the derivation time are well balanced in the entire drive range of the image pickup lens.

[0006]

In order to achieve the above object, according to the invention of claim 1, an image pickup lens capable of moving a focusing surface of a subject image and a photoelectric conversion for receiving the subject image. In an image pickup apparatus having an image pickup device that outputs the signal as an image pickup signal, the drivable range of the image pickup lens is divided into a minimum number of sections that can be interpolated, and the position of the image pickup lens is sequentially driven in the divided sections. , A focusing signal is obtained based on an image pickup signal obtained from the image pickup element at each of the driving positions, and an evaluation value obtained based on the focusing signal is interpolated to thereby set a focusing plane on the image pickup surface. A focusing position of the imaging lens for matching is derived, and the imaging lens is driven to the derived focusing position.

According to a second aspect of the present invention, in the image pickup apparatus according to the first aspect, the interpolation processing first derives an interpolation function for an interpolable section, and then interpolates at all image pickup lens drive positions within the section. The feature is that the evaluation value is derived in a pseudo manner using a function.

According to a third aspect of the present invention, in the image pickup apparatus according to the second aspect, if there is an interpolable section, the interpolation process is performed in parallel with the evaluation value acquisition process.

According to a fourth aspect of the present invention, in the image pickup apparatus according to the third aspect, as a result of the interpolation processing, the evaluation value acquisition processing and the non-interpolation processing are performed when the focus position at which the evaluation value is maximum is found. It is characterized in that the interpolation processing of the section is stopped and the imaging lens is driven to the section including the in-focus position.

According to a fifth aspect of the present invention, in the image pickup apparatus according to the fourth aspect, when it is determined as a result of the interpolation processing that the focus position is approached, fine adjustment is performed.

According to a sixth aspect of the present invention, in the image pickup apparatus according to the fifth aspect, the fine adjustment drives the image pickup lens such that a drive distance of the image pickup lens is less than a section width and is a minimum drive distance or more, and the evaluation value is obtained. Is to obtain.

In the image pickup device according to claim 5 or 6,
The focus position may be quantitatively predicted by the differential coefficient of the interpolation function, and fine adjustment may be made when the predicted focus position is approached.

In any one of claims 1 to 6 or the above-mentioned structure, before driving the image pickup lens to an initial position, an evaluation value in a section near the current drive position of the image pickup lens is obtained, If it is determined that the in-focus position exists in the vicinity, the automatic in-focus process may be performed in the direction in which the in-focus position predicted from the current lens drive position exists. This is because it is often the case that the current lens position is close to the next focus position. In this case, the differential coefficient of the interpolation function may be used to determine that the in-focus position exists in the vicinity.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an image pickup apparatus according to this embodiment. The image pickup apparatus shown in the figure includes a photographing lens 2 (zoom lens 2A, focus lens 2B), mechanical mechanism (mechanical shutter, diaphragm, filter, etc.) 101, CCD
(Charge-coupled device) 102, F / E (CDS circuit, A / D conversion circuit, AGC
(Circuit) 103, IPP 104, compression / expansion device 105, memory card
106, DRAM 107, LCD monitor 7, sub LCD 10, operation unit 108,
Motor (zoom lens motor 109A, focus motor 109
B, aperture, shutter motor 109C) 109, driver (zoom driver 110A, focus driver 110B, aperture, shutter driver 110C) 110, TG 111, battery 112, DC / AC converter 113, AC adapter 114, CPU 115, SDRAM 116 .

The photographing lens 2 is for forming an image of a subject, and includes a zoom lens 2A for realizing a zoom function and a focus lens 2B for focusing on the subject.
have. The mechanical mechanism 101 is a mechanical shutter,
It has a diaphragm and a filter for adjusting the brightness of the subject. The CCD 102 converts the subject image formed by the taking lens 2 into an electric signal and outputs it as analog image data to the F / E 103.

The F / E 103 performs preprocessing on the analog image data input from the CCD 102.
For the CDS circuit that performs correlated double sampling of the analog image data that is input from 02, the AGC circuit that adjusts the gain of the analog image data that is output from the CDS circuit, and the analog image that is output from the AGC circuit. It has an A / D conversion circuit that performs A / D conversion and outputs digital image data to the IPP 104. The IPP 104 performs various image processing on input image data. For example, F / E103
The RGB (red, green, blue) data input from is converted to YUV data. The compression / decompression circuit 105 converts YUV data into JPEG
The compressed image data stored in the memory card 106 can be compressed by JPEG.
Decompression is performed by the decompression method conforming to the method.

The DRAM 107 is a frame memory for temporarily storing captured image data, image data read from the memory card 106, and the like. Memory card 10
Reference numeral 6 is detachably attached to the digital camera body and stores compressed image data as an image file. The liquid crystal monitor 7 is for displaying image data and the like. The sub LCD 8 is for displaying the set mode and operation contents of the digital camera. The zoom driver 110A drives the zoom motor 109A in accordance with a control signal input from the CPU 115 to move the zoom lens 2A in the optical axis direction.

The focus driver 110B drives the focus motor 109B according to a control signal input from the CPU 115 to drive the focus lens 2B in the optical axis direction.
The aperture / shutter driver 110C drives the aperture / shutter motor 119C according to a control signal input from the CPU 115 to set the aperture value of the mechanical mechanism 101 and open / close the mechanical shutter of the mechanical mechanism 101. The TG 111 drives the CCD 102 and F / E 103 based on the control signal input from the IPP 104. The battery 112 is, for example, a battery such as NiCd, nickel hydrogen, or a lithium battery, and includes a DC / AC converter 113.
Converts the level of the DC voltage input from the battery 112 or the AC adapter 114 and supplies electric power to each unit of the imaging device.

The CPU 115 described above constitutes an autofocus processing mechanism. Specifically, the processing is performed by the autofocus processing program held by the CPU 115. The SDRAM 116 can also be used as a temporary storage device. If the CPU 115 includes the function of the SDRAM 116, the SDRAM 116 may be omitted in the configuration of FIG. CPU115
Is configured to divide the drivable range of the imaging lens into a plurality of sections. The CPU 115 constitutes a control means for sequentially driving the position of the image pickup lens to the boundary of the divided sections. The CPU 115 constitutes a means for interpolating the evaluation value for each section. Also, CP
The U115 serves as means for deriving an interpolation function for each section and then deriving an evaluation value for all driving positions of the imaging lens in the section in a pseudo manner using the interpolation function. That is, the CPU 115 performs all the processes (segment division, driving of the imaging lens, derivation of the interpolation function, calculation of the evaluation value), and at that time, the CPU 115 sends a command signal for driving the focus lens to the focus driver 110B.

The operation of the automatic focusing process will be described with reference to the flowchart of FIG. The autofocus processing mechanism receives the autofocus signal input from the CPU 115 and executes the processing of FIG. First, the current lens position is driven to the initial position x [0] shown in FIG. 3 (S200). Here, the lens position Lim (∞) at which the focal length is infinity is set. The present invention does not limit the initial position to this example. At the same time, from the depth of field determined based on the focal length of the zoom lens 2A and the brightness of the lens,
The section width (driving interval) is determined (S200).

Next, the evaluation value is acquired via the IPP 104 based on the image signal obtained by the CCD 102 at the present time. The acquired evaluation value is stored in the SDRAM 116 (S203). Next, it is determined whether there is an interpolable section (S204), and if an interpolable section exists, an interpolation value is given for each minimum drive interval for the interpolable section (S205). If there is no interpolable section, the process moves to the process of moving the imaging lens to the next drive position. The method of giving the interpolation value is realized by first obtaining an interpolation function that returns an evaluation value for the drive position at the boundary and substituting each drive position. As an example, the method of deriving the interpolation function is the method of deriving a third-order natural spline function. The cubic natural spline function is a continuous function of at most cubic that smoothly passes through a sample point (in the example shown in FIG. 3, a point Y [i] at which the evaluation value at the boundary of each section is plotted), and any driving It has the feature that the first and second derivatives can be obtained at the position.

The tendency of the interpolated section is examined to determine whether the in-focus position is already known (S206). If the in-focus position is known, the image pickup lens is driven to the in-focus position and the processing is ended (S207, S208). here,
A method of determining the in-focus position will be described. First, a method of determining the maximum value of the mountain is shown in the example of FIG. Interpolation is now complete from section C1 to section C7. In the example of FIG. 3, there is the maximum evaluation value y [f] at the driving position f within the section C7. Where x
Find the first derivative d1 and the second derivative d2 of the interpolation function in [7]. Intuitively, d1 is the slope of the curve at that point, and d2 is the rate of increase of the slope. Here, the error dn due to noise is defined, and d1 <−dn and d
If 2 <0, x [f] is determined to be the in-focus position. However, in the above example, when the maximum value of the mountain exists and the evaluation value is gradually decreasing, it cannot end immediately, so the boundaries x [m] and x [m + 1] of the adjacent sections Also, when the condition of d1 <-dn is satisfied three times in a row at x and [m + 2], that is, when the lens position f is passed and the value is decreased three times in a row, the same is done. However, regarding the latter condition, the present invention does not limit the determination condition to the above.

If the in-focus position is not known, it is then determined whether or not the in-focus position can be estimated to be in the vicinity (S209). Here, a method of determining that the in-focus position is in the vicinity is shown in the example of FIG. It is assumed that the interpolation is completed from the section C1 to Ck. In this situation, the in-focus position is determined to be in the vicinity by determining the first-order differential coefficient d1 and the second-order differential coefficient d2 in x [k] and using the error dn due to noise to calculate d.
If 1> dn and d2 <0, it is determined that the focus position is in the vicinity.
In the case of FIG. 4, when k = 4, it is determined that the focus position is in the vicinity. If the focus position can be estimated to be in the vicinity, the process moves from the next section to a more accurate fine adjustment process (S210).
If the focus position cannot be estimated to be in the vicinity, the imaging lens is driven to the next drive position and the process returns to the beginning of the loop.
(S211).

A highly accurate fine adjustment process will be described with reference to the flowchart of FIG. During fine adjustment, the lens is driven not only at the boundary of the section but also within the section to obtain the evaluation value.
(S222, S223), the accuracy of interpolation is increased (this corresponds to the fine adjustment section in FIG. 4). The condition for ending the fine adjustment is when the in-focus position is known or when it is determined that there is no in-focus point in the vicinity, and fine adjustment is no longer necessary. Condition for ending fine adjustment processing (S22
As an example of 4), in FIG. 4, the first-order differential coefficient d1 and the second-order differential coefficient at x [k], which is the end point of the range where interpolation is completed, are performed.
This is the case where d2 is obtained and d1 <-dn or d2> 0 is satisfied using the noise error dn. In the case of FIG. 4, when k = 10, the condition for ending the fine adjustment process is satisfied, and the fine adjustment process is ended from the next stage.
(S225, S226).

The flow charts of FIGS. 6 and 7 (preparation processing) and FIG. 8 (main processing) are x when starting the automatic focusing processing.
When the imaging lens at [0] is driven to the initial position, the initial position can be determined by acquiring evaluation values for x [1], x [2], x [3] and x [4] in the vicinity of the driving direction. The example which adds the process which changes is shown. For example, in the example of FIG. 6A, since it is possible to predict that the in-focus position exists in the direction opposite to the driving direction with respect to the current imaging lens position by the determination method using the differential coefficient, the current imaging lens position is set to the initial position. Then, automatic focusing processing (S202 to S212 in FIG. 8) is performed in the direction in which the focusing position exists. In the example of FIG. 6B, similarly, it can be predicted that the in-focus position exists in the driving direction. Therefore, the current imaging lens position is set as the initial position, and the automatic in-focus process is performed in the direction in which the in-focus position exists (see FIG. 8 S202 to 212) is performed. Also,
In the example of FIG. 9, since the existing direction of the in-focus position cannot be specified, the initial position is set to the specified position lim (∞), and the automatic in-focus process (S202 to S212 in FIG. 8) is performed.

[0026]

According to the first aspect of the present invention, an image pickup lens capable of moving a focusing surface of a subject image, and an image pickup device which outputs a signal obtained by receiving the photoelectric conversion of the subject image as an image pickup signal. In the image pickup apparatus having the above-mentioned, the drivable range of the image pickup lens is divided into a minimum number of sections that can be interpolated, and the position of the image pickup lens is sequentially driven in the divided sections, and the image pickup device is driven at each of the drive positions The focus signal is obtained based on the obtained image pickup signal, and the evaluation value obtained based on the focus signal is interpolated to obtain the focus of the image pickup lens for matching the focus plane with the image pickup surface. Since the position is derived and the imaging lens is driven to the derived in-focus position, the interpolation accuracy can be reliably obtained, and the accuracy of the in-focus position in the entire driving range of the imaging lens can be obtained. Out can ensure the balance of the time.

According to a second aspect of the present invention, in the image pickup apparatus according to the first aspect, the interpolation processing first derives an interpolation function for an interpolable section, and then all image pickup lens drive positions in the section. Since it was decided to derive the evaluation value in a pseudo manner using the interpolation function in, the derivation of the interpolation function allows the focus position to be derived efficiently without being affected by the focal length of the lens or the F number. . In addition, by reducing the number of times the lens is actually driven, it is possible to contribute to speeding up the focusing operation.

According to a third aspect of the invention, in the image pickup apparatus according to the second aspect, if there is an interpolable section, the interpolation processing is performed in parallel with the evaluation value acquisition processing. By parallelizing the interpolation processing, which is a software processing, and the driving of the imaging lens, which is a mechanical processing, the focusing processing can be performed at a higher speed than a case where both operations are sequentially performed.

According to a fourth aspect of the present invention, in the image pickup apparatus according to the third aspect, when the result of the interpolation processing is the focus position where the evaluation value is maximum, the evaluation value acquisition processing and Since the interpolation processing in the interpolation section is stopped and the image pickup lens is driven to the section including the in-focus position, unnecessary focusing of the lens is omitted, so that the focusing processing can be speeded up.

According to the fifth aspect of the invention, in the image pickup apparatus according to the fourth aspect, when it is determined as a result of the interpolation processing that the focus position is approached, fine adjustment is made, so the focus processing time It is possible to improve the accuracy of the in-focus position derived by the interpolation function calculation without degrading.

According to a sixth aspect of the present invention, in the image pickup apparatus according to the fifth aspect, the fine adjustment drives the image pickup lens by setting the drive distance of the image pickup lens to be less than the section width and not less than the minimum drive distance. Since it is decided to obtain the evaluation value, it is possible to improve the accuracy of the focus position derived by the interpolation function calculation without impairing the focus processing time, and the control itself is easy, which puts a load on the calculation processing. Absent.

In the image pickup device according to claim 5 or 6,
If the in-focus position is quantitatively predicted by the differential coefficient of the interpolation function and a fine shift is made when the predicted in-focus position is approached, the tendency of the interpolation function in the immediately following section can be predicted, so it is almost optimal. It is possible to shift to fine adjustment at that time, and it is possible to shorten the focusing processing time and improve the accuracy of the focusing position.

In any one of claims 1 to 6 or the above structure, before driving the image pickup lens to an initial position, an evaluation value in a section near the current drive position of the image pickup lens is obtained, If it is determined that there is a focusing position in the vicinity, if the automatic focusing process is performed in the direction in which the focusing position predicted from the lens driving position at the present time exists, the position of the imaging lens and the focusing position are determined. When the positions are close to each other, the focus position can be derived in a shorter time. Further, in this configuration, when the differential coefficient of the interpolation function is used to determine that the in-focus position exists in the vicinity, when the change in the middle of the section is large, the in-focus position is relative to the current position of the imaging lens. Since it is immediately known in which direction the focus position can be derived in a shorter time.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of an image pickup apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart of automatic focusing processing.

FIG. 3 is a graph for explaining an example of determining a focus position.

FIG. 4 is a graph for explaining an example of fine adjustment control.

FIG. 5 is a flowchart of a fine adjustment process.

FIG. 6 is a graph for explaining prediction of a focus position at the initial stage of processing.

FIG. 7 is a flowchart of a preparation process in an automatic focusing process.

FIG. 8 is a flowchart of main processing in automatic focusing processing.

FIG. 9 is a graph for explaining the prediction of the in-focus position when the driving direction of the imaging lens at the initial stage of processing is not known.

FIG. 10 is a graph for explaining a conventional problem.

FIG. 11 is a graph showing a legend of a focus position.

[Explanation of symbols]

2A, 2B imaging lens 102 CCD as an image sensor

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 5/232 G03B 3/00 A

Claims (6)

[Claims] 1. An image pickup apparatus comprising: an image pickup lens capable of moving a focal plane of a subject image; and an image pickup element for receiving a signal obtained by photoelectrically converting the subject image and outputting the signal as an image pickup signal. The drivable range is divided into a minimum number of sections that can be interpolated, the position of the image pickup lens is sequentially driven into the divided sections, and a focusing signal is obtained based on the image pickup signal obtained from the image pickup device at each of the driving positions. Is calculated and the evaluation value obtained based on the focusing signal is interpolated to derive the focusing position of the imaging lens for matching the focusing surface with the imaging surface. An image pickup apparatus characterized in that the image pickup lens is driven to a focal position. 2. The image pickup apparatus according to claim 1, wherein the interpolation processing first derives an interpolation function for an interpolable section, and then uses an interpolation function at all image pickup lens drive positions in the section to generate a pseudo-function. An image pickup apparatus, comprising: deriving an evaluation value according to. 3. The image pickup apparatus according to claim 2, wherein if there is an interpolable section, the interpolation processing is performed in parallel with the evaluation value acquisition processing. 4. The image pickup apparatus according to claim 3, wherein the evaluation value acquisition process and the interpolation process for the non-interpolated section are stopped when the focus position where the evaluation value is the maximum is found as a result of the interpolation process. Then, the image pickup apparatus drives the image pickup lens in a section including a focus position. 5. The image pickup apparatus according to claim 4, wherein when the result of the interpolation processing indicates that the focus position is approached, fine adjustment is performed. 6. The image pickup device according to claim 5, wherein the fine adjustment drives the image pickup lens such that a drive distance of the image pickup lens is less than a section width and not less than a minimum drive distance,
An image pickup apparatus characterized by obtaining the above evaluation value.