JP2006049995A - Image reading apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reader capable of identifying and correcting the spectral reflectance characteristic of a multilayer film interference filter varied by an incident angle to the filter. <P>SOLUTION: The image reader including: a light source 107 for illuminating an original; an image forming lens 105 for reducing and coupling reflected light from the original 102 illuminated by the light source 107; a line sensor 106 for applying photoelectric conversion to the formed original image; and a multilayer film interference filter 108 located in the optical path of an image reading optical system and acting like an infrared ray cut-off filter, is provided with a spectral characteristic correction means 1107 for identifying and correcting the spectral characteristic of the multilayer film interference filter 108 at its main scanning position by reading a particular member. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image reading apparatus having an infrared cut component in an optical path, and an image forming apparatus such as a digital copying machine and a facsimile equipped with the image reading apparatus.

In an image reading apparatus that reads a color original, a halogen lamp, a fluorescent lamp, or a xenon lamp is used as a light source of an optical scanning system that reads the color original. On the other hand, as a line sensor used in an image reading apparatus, a CCD is generally used.
The spectral characteristics of the CCD have high sensitivity up to the infrared region, and the light source also has sensitivity up to the infrared region. Therefore, when the read document has spectral reflectance up to the infrared region. As a CCD output, an output including the spectral reflectance up to the infrared region of the document can be obtained.
On the other hand, the spectral sensitivity of the human eye does not have sensitivity up to the infrared region (visibility characteristics), so the output including the spectral reflectance up to the infrared region of the document differs from the actual document color. Degradation of color reproducibility occurs.
In order to improve color reproducibility, an infrared light cut component has been conventionally arranged in an optical path of an image reading optical system. As an infrared light cut component, an infrared light absorption filter and a multilayer interference filter are often used. Since the infrared light absorption filter is formed of a colored optical material having light absorption characteristics, it is necessary to increase the light amount of the light source, and there are disadvantages such as heat generation and a decrease in the light source lifetime. Further, it is necessary to dispose them as individual parts in the optical path of the image reading optical system, which increases the cost of the apparatus. Multi-layer interference filters control the spectral characteristics using light interference. By controlling the number, thickness, and material of the film, the transmittance in a wavelength range other than the target cut wavelength is reduced. There is a feature that can be suppressed relatively. Also, by coating the imaging lens with a multilayer interference filter by vapor deposition, a space for arranging the components is not required, and the apparatus can be reduced in size and cost. However, in general, the multilayer interference filter has a problem that the spectral transmittance changes in accordance with the incidence accuracy of a light beam (light beam).
For example, as shown in FIG. 3, the spectral transmittance of the light beam transmitted through the multilayer interference filter at an incident angle of 0 ° and the spectral transmittance of the light beam transmitted through the multilayer interference filter at an incident angle of 20 ° as shown in FIG. Different. That is, as the incident angle increases, the spectral transmittance shifts to the short wavelength side.
Therefore, for example, in Patent Document 1, a colored optical material having light absorption characteristics is used as a material of an imaging lens as an infrared light cut component, and wavelength selection is performed on at least one surface of the lens using the colored optical material. A device capable of canceling a change in spectral transmittance due to an incident angle by applying a multilayer interference filter having a property and combining characteristics of the infrared light absorption filter and the multilayer interference filter has been proposed.
For example, Patent Document 2 uses a xenon lamp as a light source, avoids a red peak of spectral characteristics of the light source, and multi-layers depending on an incident angle between 630 to 680 nm where the light emission amount decreases at a wavelength equal to or higher than the red peak. There has been proposed an apparatus that can reduce the influence on the image characteristics by changing the spectral transmittance of the film interference filter.
JP-A-6-273694 Japanese Patent Laid-Open No. 2000-307806

However, in Patent Document 1, it is necessary to increase the light amount of the light source in order to form a lens with a colored optical material having light absorption characteristics. Increasing the amount of light affects energy efficiency, light source temperature, and light source life. In addition, the material forming the lens leads to an increase in cost, and the shape of the lens using the colored optical material is almost determined in order to offset the angle of view characteristics of the multilayer interference filter. There is a problem that is limited. Furthermore, since the refractive index and the dispersion constant also change when the lens is colored, there is a problem that management is very difficult.
Further, in Patent Document 2, the influence on the image characteristics cannot be completely eliminated, and the influence is not negligible with respect to the document having the spectral reflectance characteristic from the wavelength near the red peak of the xenon lamp. In addition, when considering variations in the spectral characteristics of the xenon lamp, variations in the spectral transmittance due to the incident angle of the multilayer interference filter characteristics, and variations between lots, the variation from the red peak wavelength of the xenon lamp is taken into account. It is necessary to determine the wavelength at which the spectral transmittance decreases in consideration. As a result, the infrared light cut characteristics that are the original purpose cannot be sufficiently obtained.
An object of the present invention is to provide an image reading apparatus and an image forming apparatus capable of identifying and correcting characteristics in which the spectral reflectance characteristics of a multilayer interference filter differ depending on the incident angle to the filter.

In order to achieve the above object, an invention according to claim 1 is directed to a light source, an imaging lens for reducing and coupling reflected light of a document illuminated by the light source, and a line sensor for photoelectrically converting the imaged document image. In the image reading apparatus in which a multilayer interference filter as an infrared light cut filter is provided in the optical path where the and are arranged, the spectral characteristics at the main scanning position of the multilayer interference filter are identified by reading a specific member. Spectral characteristic correction means for correcting is provided.
The invention described in claim 2 is characterized in that the spectral characteristic correction processing in the spectral characteristic correction means can be selected.
The invention according to claim 3 further comprises image level determination means for determining the image level, and on / off of the spectral characteristic correction processing of the spectral characteristic correction means based on the determination result of the level determination means. Features.
The invention according to claim 4 is characterized in that the multilayer interference filter is formed by evaporating a multilayer interference coating on glass.
The invention according to claim 5 is characterized in that the multilayer interference filter is formed by depositing multilayer interference coating on the imaging lens.
According to a sixth aspect of the present invention, the image reading apparatus according to any one of the first to fifth aspects is provided.

  According to the present invention, an image reading optical system having a light source that illuminates a document, an imaging lens that reduces and couples reflected light of the document illuminated by the light source, and a line sensor that photoelectrically converts the imaged document image. SPECIFICATION CHARACTERISTIC CORRECTION UNIT FOR IDENTIFYING AND CORRECTING SPECTRAL CHARACTERISTICS AT MAIN SCANNING POSITION OF MULTILAYER INTERFERENCE FILTER BY READING SPECIFIC MEMBER IN IMAGE READING DEVICE HAVING MULTILAYER INTERFERENCE FILTER AS INFRARED LIGHT CUT FILTER IN OPTICAL PATH It is possible to achieve the intended purpose.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a configuration diagram of an image reading apparatus according to an embodiment of the present invention. Hereinafter, the configuration will be described together with the operation.
An illumination optical system having a light source 107 disposed below the contact glass 101 illuminates the original 102, the reference white plate 109, and the reference color plate 110. The reflected illumination light is reflected and deflected by the first mirror 103a of the first traveling body 103 and then sequentially reflected and deflected by the first mirror 104a and the second mirror 104b of the second traveling body 104. The light is guided to the imaging lens 105 and is reduced and coupled onto the incident surface of the line sensor (CCD) 106 by the imaging lens 105.
At the time of the reading operation, the first traveling body 103 moves to the position 103 ′ at the speed V, and at the same time, the second traveling body 104 moves at half the speed of the first traveling body 103, that is, V / 2. It moves to the position 104 ′ and reads the entire longitudinal direction in the order of the reference white plate 109, the reference color plate 110, and the original 102.
The infrared light cut filter of the present invention is a multilayer interference filter formed by depositing multilayer interference coating, and can be placed at any position between the original surface and the light receiving surface of the line sensor 106. It is.
For example, as shown in FIG. 1, the multilayer interference filter 108 a is disposed on the object side of the imaging lens 105, or the multilayer interference filter 108 b is disposed on the image side of the imaging lens 105.
A multilayer interference filter 108 is formed on one surface of the imaging lens shown in FIG.
In general, the multilayer interference filter 108 is formed on a flat surface in consideration of manufacturing conditions such as thick film control and adhesion strength.

FIG. 3 is a diagram showing light fluxes with incident angles of 0 ° and 20 °, and FIG. 4 is a diagram showing spectral transmittance characteristics of the multilayer interference filter.
For example, as shown in FIG. 3, the spectral transmittance of a light beam transmitted through a multilayer interference filter at an incident angle of 0 ° and the spectral transmittance of a light beam transmitted through the multilayer interference filter at an incident angle of 20 ° as shown in FIG. Further, the spectral transmittance changes depending on the incident angle to the multilayer interference filter 108. As the incident angle increases, the spectral transmittance shifts to the short wavelength side. The above characteristics are affected by component variations.
FIG. 5 is a diagram showing the spectral sensitivity characteristics of the CCD. The red spectrum has sensitivity up to the infrared region. Generally, 380 to 780 nm is defined as the visible light region. The sensitivity of the human eye to light is defined as the visibility, and this visibility varies depending on the wavelength, and is the strongest at the wavelength of 555 nm.
In general, the standard visibility is defined as about 400 to 700 nm. From the above, the visibility of the human eye decreases as it goes to the short wavelength and long wavelength side, so having more sensitivity than necessary on the short wavelength and long wavelength side is accompanied by deterioration of color reproducibility. Become.
FIG. 6 shows the spectral characteristics of the light source. It has spectral characteristics even in a wavelength region of 700 nm or more.
FIG. 7 shows the spectral reflectance of the original. In FIG. 7, as an example, a white plate that defines the reference white of the image reading apparatus, a gray having a relatively flat spectral characteristic, and a black spectral reflectance having a spectral reflectance from the infrared region (long wavelength region). Is shown. Further, as the spectral reflectance of the reference color plate 110, for example, a black color having spectral reflectance from the infrared region (long wavelength region) shown in FIG. 7 is used.
The output image data from the image reading device is subjected to the following shading processing from white plate data and document data, and corrections such as uneven sensitivity of each pixel of the line sensor 106, variation in transmitted light amount of the lens, unevenness and deterioration of the illumination / optical system, etc. Do.
Output image data = original data / white plate data × 255 (in the case of 8 bits)
(Strictly speaking, processing such as black level correction is included, but it is not described here.)
White plate data and document data are integrated values of all the colors of the document reflectance, light source spectrum, multilayer interference filter transmittance, and CCD spectral sensitivity characteristics. From the above, values corresponding to red, green, and blue are output as RGB output data.

FIG. 8 shows the relative spectral output of the red component of the white plate. FIG. 8 shows a difference in output when the incident angles to the multilayer interference filter 108 shown in FIG. 4 are 0 ° and 20 °.
FIG. 9 shows the relative spectral output of the red component of the gray document shown in FIG. FIG. 9 shows the difference in output when the incident angles to the multilayer interference filter 108 shown in FIG. 4 are 0 ° and 20 °.
FIG. 10 shows the relative spectral output of the red component of the black document shown in FIG. FIG. 10 shows the difference in output when the incident angles to the multilayer interference filter 108 shown in FIG. 4 are 0 ° and 20 °.
The integration results of the white plate, gray, and black red components are shown below. Here, the ratio when the incident angle to the multilayer interference filter 108 is 20 ° is shown when the incident angle 0 ° is 100%.
White board = 94.00%
Gray = 94.05%
Black = 89.77%
As described above, when the spectral characteristic of the original is flat, it is possible to cancel the difference in spectral transmittance due to the incident angle to the multilayer interference filter 108 by performing the shading process.
However, in the original such as the black original in which the spectral reflectance of the original increases in the infrared region, the difference in the spectral transmittance due to the incident angle to the multilayer interference filter 108 can be canceled by performing the shading process. Can not.
The above shows that the red output image level fluctuates depending on the main scanning location as the output of the image reading apparatus.

FIG. 11 is a block diagram showing a first example of the spectral transmittance correction processing unit in the image reading apparatus of the present invention. The read data read by the one-dimensional line-shaped CCD 106 undergoes signal processing by the signal processing circuit 1102 such as waveform shaping, sample hold, and amplification, and is converted into digital data by the A / D converter 1103, and is then sent to the shading correction circuit 1104. Entered.
The path switching circuit 1108 receives the output image data from the shading correction circuit 1104 and a reference color plate selection signal indicating the reference color plate reading period. When the reference color plate reading period is indicated, output image data is output to the area averaging circuit 1105. The area averaging circuit 1105 can select an area obtained by dividing the main scanning of the image into an arbitrary number.
For example, in the case of the CCD 106 having 7500 pixels in the main scanning, when the number of divisions in the main scanning is designated as 75 and the number of sub-scanning pixels is designated as 100, an average value of 100 × 100 pixels divided into 75 in the main scanning direction is calculated. Is done.
Average value = a1, a2... A75
Next, the coefficient calculation circuit 1106 calculates a correction coefficient using the value calculated by the area average circuit 1105.
In the case of the above example, the reference area is selected from 75 in the CPU not shown. The coefficient of each area is calculated with respect to the average value of the selected reference areas. For example, when the average value a32 is designated as the reference area, the coefficient of each area is calculated as follows.
Coefficient n = a32 / an (n = 1, 2,... 75)
The coefficients are stored in a memory inside the subsequent spectral characteristic correction circuit 1107.
On the other hand, when the reference color plate selection signal indicates a period other than the reference color plate reading period to the path switching circuit 1108, image data is output to the spectral transmittance correction circuit 1107. Here, the variation in the image data due to the difference in the incident angle on the multilayer interference filter 108 is corrected by multiplying the image data by the correction coefficient determined by the main scanning position. The corrected red image is output to a subsequent image processing block (not shown). Further, the output of the shading circuit 1104 is output to a subsequent image processing block (not shown) as a blue and green image.

In the above configuration, variations in image data are corrected in the following steps.
First, after the first traveling body 103 and the second traveling body 104 shown in FIG. 1 move to start the reading operation, shading correction data is generated by a known technique when the reference white plate 109 is read. Next, when the reading operation is continued and the reference color plate 110 is read, a coefficient for spectral characteristics is stored in the internal memory of the spectral characteristic correction circuit 1107 shown in FIG. Further, when the original is read following the reading operation, the correction coefficient stored in the spectral characteristic correction circuit 1107 is calculated with the image data to correct the variation in the image data due to the difference in the incident angle to the multilayer interference filter 108. It will be.
By making the number of divisions of the area average circuit 1105 fine, the correction accuracy can be improved. As the finest division number, processing in units of main scanning pixels can be considered. In order to reduce the influence of noise, the number of sub-scanning lines in the area averaging circuit 1105 is increased. The original used in the reference black original reading mode can use any image depending on the target image characteristics of each image reading apparatus.
The coefficient calculation calculation and the spectral transmittance correction calculation method described above are only examples, and calculation methods other than the above can be adopted by adopting the configuration of the image reading apparatus. In the above embodiment, only the correction of the red component is described. However, when the spectral characteristics of the blue component and the green component change depending on the incident angle of the multilayer interference filter 108, the correction for the blue component and the green component can be easily performed. Is possible.

FIG. 12 is a configuration diagram showing a second example of the spectral transmittance correction processing unit in the image reading apparatus of the present invention. A correction ON / OFF circuit 1109 and an operation unit 1110 are added to the configuration shown in FIG.
Under the control from the operation unit 1110, the correction ON / OFF circuit 1109 outputs the input data from the spectral characteristic correction circuit 1107 when the correction is ON. When the correction is OFF, output data of the shading circuit 1104 is output via the path switching circuit 1108. As described above, correction ON / OFF control can be performed.
FIG. 13 is a block diagram showing a third example of the spectral transmittance correction processing unit in the image reading apparatus of the present invention. An image level determination circuit 1111 is added to the configuration shown in FIG.
The image level determination circuit 1111 outputs, for example, “L” as a determination control signal if the input image data level is equal to or higher than a predetermined image data level, and if the image data level is equal to or lower than the threshold level. Then, “H” is output as the determination control signal. The spectral transmittance correction circuit 1107 internally switches correction ON / OFF in units of pixels based on the determination control signal logic. As described above, ON / OFF control of the correction based on the threshold level of the image data can be performed.
In the present invention, it is possible to prevent deterioration in color reproducibility due to the spectral reflectance characteristics of the multilayer interference filter 108 being different depending on the incident angle to the filter. In addition, since a member for performing the correction process is provided in the apparatus, it is not necessary to readjust even when a member related to the spectrum, such as an infrared light cut filter, is exchanged, and the maintenance is excellent.
In addition, it is possible to select an optimum process depending on the type of document, and it is possible to further improve color reproducibility by enabling execution selection according to presetting when a problem occurs in the market or the like.
In addition, it is not necessary to increase the amount of light from the light source compared to the case of forming an infrared light cut filter with colored optical material glass having light absorption characteristics, and the installation space is not required, so the size and cost of the apparatus can be reduced. It becomes.

1 is a configuration diagram of an image reading apparatus according to an embodiment of the present invention. The figure which shows a mode that the multilayer film interference filter was formed in one surface of an imaging lens. The figure which shows the light beam of incident angles 0 degree and 20 degrees. The figure which shows the spectral transmittance characteristic of a multilayer interference filter. The figure which shows the spectral sensitivity characteristic of CCD. The figure which shows the spectral characteristic of a light source. The figure which shows the spectral reflectance of a manuscript. The figure which shows the relative spectral output of the red component of a white board. The figure which shows the relative spectral output of the red component of the gray original shown in FIG. The figure which shows the relative spectral output of the red component of the black original shown in FIG. The block diagram which shows the 1st example of the spectral transmittance correction process part in the image reader of this invention. The block diagram which shows the 2nd example of the spectral transmittance correction | amendment process part in the image reading apparatus of this invention. The block diagram which shows the 3rd example of the spectral transmittance correction | amendment process part in the image reading apparatus of this invention.

Explanation of symbols

102 manuscript, 105 imaging lens, 106 line sensor, 108 multilayer interference filter, 1107 spectral transmittance correction circuit (spectral transmittance correction means)

Claims (6)

  A multilayer as an infrared light cut filter in an optical path in which a light source, an imaging lens that reduces and couples reflected light of a document illuminated by the light source, and a line sensor that photoelectrically converts the imaged document image are arranged An image reading apparatus provided with a film interference filter, comprising: spectral characteristic correction means for identifying and correcting the spectral characteristic at the main scanning position of the multilayer film interference filter by reading a specific member. Reader.   The image reading apparatus according to claim 1, wherein spectral characteristic correction processing in the spectral characteristic correction unit can be selected.   2. The image level determining means for determining an image level is further provided, and spectral characteristic correction processing of the spectral characteristic correcting means is turned on / off based on a determination result of the level determining means. Image reading device.   2. The image reading apparatus according to claim 1, wherein the multilayer interference filter is formed by depositing a multilayer interference coating on glass.   2. The image reading apparatus according to claim 1, wherein the multilayer interference filter is formed by depositing multilayer interference coating on an imaging lens. An image forming apparatus comprising the image reading apparatus according to claim 1.

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