JP2007088557A - Method of calculating inter-color crosstalk correction formula, and image reading apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly precisely correct inter-color crosstalks of an image reading apparatus. <P>SOLUTION: The image reading apparatus 50 reads each color chart 31 of a calibration original 30 to obtain color chart actual measurement output value data 54 of each color chart 31; whereas the method obtains color chart ideal output value data 42 under the assumption of reading each color chart in an ideal state by the image reading apparatus 50 without crosstalks, by using color chart spectral colorimetric data 32 of each color chart, sensor spectral sensitivity data 34 of a CCD sensor of the image reading apparatus 50, illumination light source spectral distribution data 36 for an original illumination light source of the image reading apparatus 50, and an image forming system spectral distribution data 38 of an image forming optical system of the image reading apparatus 50. A crosstalk correction formula calculation section 60 calculates a crosstalk correction matrix 62 so that the color chart actual measurement output value data 54 and the color chart ideal output value data 42 become minimum in the color charts as a whole. Crosstalks are corrected by using this matrix. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a calculation method of a correction formula for correcting crosstalk between colors of an image reading apparatus such as a color scanner using a color sensor, and to crosstalk correction using the method.

  Up to now, development of cost reduction and high definition of an image reading apparatus using a solid-state imaging device such as a color CCD such as a color scanner has been advanced.

  Currently, color CCDs that are widely used realize color information reading by a technique called an on-wafer color filter that forms red, green, and blue color filters on a CCD chip.

  However, in the case of such a color CCD, the output of each color of R (red), G (green), and B (blue), which should be independent from each other, due to the influence of the circuit configuration in the chip and filter leakage light, etc. In many cases, a phenomenon called crosstalk is generated which affects and changes.

  FIG. 1 shows an output signal of a color CCD in which crosstalk actually occurs. This is a graph showing a change in output when the color linear CCD sensor 10 reads the original 100 that suddenly changes from black to white as shown in FIG. In the graph of FIG. 1, the vertical axis represents the average value of the output signals of the pixels for each R, G, or B channel, and the horizontal axis represents the movement distance of the original 100 along the original feed direction indicated by the arrow in FIG. Have taken. When the original 100 as shown in FIG. 2 is read, since the black area is first read for each color channel, the pixel value is small, and then the original image changes abruptly from black to white. When approaching the position, the pixel value increases rapidly. Here, the R, G, and B channels on the color linear CCD sensor 10 are arranged with a predetermined gap (interval) therebetween, so that the moving distance of the document 100 is taken on the horizontal axis as shown in FIG. In this case, the rise of the graph of the pixel value of each channel is shifted by the gap. In the output change shown in FIG. 1, the pixel value is lowered immediately before the B channel graph rises due to the influence of crosstalk. This is lower than the pixel value corresponding to the actual document 100 under the influence of the sudden rise of other channel signals.

  Such a crosstalk phenomenon is not preferable because it appears as an edge coloring on the image and leads to a decrease in color reproducibility due to color mixing.

  Up to now, the reduction of the crosstalk phenomenon has been dealt with by devising the device in the manufacturing process and the circuit configuration in the chip.

  For example, in Patent Document 1, crosstalk between adjacent signal lines can be corrected based on the relational expression between the potentials of three common signal lines adjacent to each other and the coupling capacitance and load capacitance between them. There has been proposed an image reading apparatus capable of correcting an afterimage remaining in the light receiving element based on a relational expression between the scan data for the previous time and the current time and the capacitance of the photodiode portion and the wiring portion.

  However, in these methods, it is necessary to obtain in advance a characteristic value unique to the image sensor such as capacitance, and in fact, it can be applied only when the manufacturer of the image sensor newly designs / produces or designs a peripheral circuit. Moreover, it is necessary to apply to each type of image pickup device individually, and when applying to image pickup devices of different types, it is necessary to redesign most of the circuits.

  In Patent Document 2, a display is used for crosstalk correction. Make the display emit light of a single color phosphor, and minimize the output value of the color channel of the CCD that does not correspond to this monochromatic light (if the display is emitting red light, the green and blue channels of the CCD) The crosstalk is corrected by controlling the programmable attenuator.

  However, this correction method requires in principle that the spectral distribution of the monochromatic phosphor of the display matches the spectral sensitivity of the corresponding CCD monochromatic channel. However, since the emission distribution of the phosphor of the display and the spectral sensitivity of the CCD do not normally match, it is considered that the effect of improving the crosstalk by this method is small.

JP 05-316348 A Japanese Patent Laid-Open No. 08-149500

  Therefore, the present invention is applicable to an existing image sensor and provides a method for accurately correcting intercolor crosstalk.

  The method according to the present invention is a method for calculating a correction formula for inter-color crosstalk correction in an image reading apparatus that detects and reads light from an original by each light receiving unit for each color, and the spectral reflectance is measured. In accordance with the spectral reflectance data of the plurality of color charts and the spectral sensitivity characteristic data for the respective colors of the image reading apparatus, the image reading apparatus is in an ideal state without crosstalk between colors. The step of obtaining ideal output value data when it is assumed that it has been read, the step of actually reading each color chart with the image reading device to obtain the measured output value data of each color chart, the ideal output value data and the actual measurement Obtaining a correction formula for inter-color crosstalk so that a difference from output value data is minimized in the whole of the plurality of color charts.

  In a preferred aspect of the present invention, the spectral sensitivity characteristic data for each color of the image reading device includes spectral sensitivity data of the light receiving portion of each color, spectral distribution data of a light source for document illumination provided in the image reading device, and And spectral distribution data of an imaging optical system provided in the image reading device.

  The image reading apparatus according to the present invention is an image reading apparatus that detects and reads light from a document by each light receiving unit for each color, and intercolor crosstalk with respect to an image signal obtained by reading the document. It is assumed that the crosstalk correction calculation unit performs correction calculation, and the crosstalk correction calculation unit reads a plurality of color charts whose spectral reflectances are measured in an ideal state without intercolor crosstalk. The difference between the ideal output value data and the actually measured output value data obtained by actually reading the plurality of color charts with the image reading apparatus is minimized between the plurality of color charts. A crosstalk correction calculation between colors is performed on the image signal using a crosstalk correction formula.

  Further, in a preferred aspect of the image reading apparatus according to the present invention, the crosstalk correction calculating unit converts color signals detected by the light receiving unit into signals of a predetermined color space. A color space conversion process and a crosstalk correction process are performed simultaneously by performing a calculation that combines the calculation and the calculation of the inter-color crosstalk correction formula.

  In another preferable aspect of the image reading apparatus according to the present invention, the crosstalk correction calculation unit includes a shading correction calculation for the signals of each color detected by the light receiving unit, and a correction formula for the intercolor crosstalk. The shading correction process and the crosstalk correction process are performed at the same time.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 3 is a block diagram showing a flow of image signals and processing of a general image reading apparatus using a color linear CCD sensor 10 (hereinafter simply referred to as sensor 10). Similar to the color line CCD sensor 10 of FIG. 2, the sensor 10 includes line sensors for R, G, and B channels.

  The optical information of the original is imaged on the sensor 10 by the optical system. The CCD of each channel of the sensor 10 converts the light that has passed through the R, G, and B color filters into an electrical signal and outputs it as an independent analog signal for each of R, G, and B.

  Analog electric signals output from the R, G, and B channels of the sensor 10 are amplified by analog amplifiers 12R, 12G, and 12B, and converted into digital signals by A / D converters 14R, 14G, and 14B. .

  In order to correct the nonuniformity of the optical system and the sensitivity variation of each pixel on the CCD line with respect to the digital signals of the R, G, B channels generated in this way, a known shading is performed by the shading correction units 16R, 16G, 16B. Correction processing is performed. As is well known, in shading correction, for example, based on the output value of each pixel on the CCD line when reading a white uniform reference plate, a correction coefficient for making the output value of each pixel constant is used. Obtained for each pixel. Then, the digital signal of each pixel at the time of actual imaging is corrected using a correction coefficient corresponding to the pixel.

  Next, line gap correction is performed. As shown in FIG. 2, the light receiving elements of each line of the sensor 10 are arranged in the main scanning direction, and are arranged with a certain interval in the sub scanning direction for each of the R, G, and B color channels. The interval in the sub-scanning direction between the color channels is called a line gap. Due to this line gap, when the main scanning reading of each color channel is performed while the sensor 10 and the document are relatively moved in the sub-scanning direction, a time difference occurs when the CCD line of each color channel reads the same position on the document. In order to correct this time difference so that the R, G, B signals at the same position on the document are aligned at the same time in time, the line gap correction unit 18 outputs the signals of the R, G, B color channels. Output necessary ones with a delay. This process is called a line gap correction process. In the arrangement of each color channel as shown in FIG. 2, the R channel signal is delayed by two line gaps, and the G channel signal is delayed by one line gap, thereby aligning with the B channel signal. The line gap correction unit 18 is provided with a buffer 19 for this delay processing.

  The signals of the R, G, and B channels thus aligned are input to the color space conversion unit 20. The color space conversion unit 20 converts color values in a device-dependent color space represented by RGB into color values in a device-independent color space such as CIE L * a * b *. In this color space conversion process, a matrix operation is performed as is well known, and as a result, a read image signal is output.

  Normally, in the image reading apparatus, each processing circuit after the A / D converters 14R, 14G, and 14B can be set to output the input signal as it is without performing any processing.

  Next, a method for calculating the crosstalk correction formula in this embodiment will be described. FIG. 4 shows a system configuration for calculating the crosstalk correction formula. This system is for calculating a crosstalk correction formula for the image reading apparatus 50.

  In the calculation of the crosstalk correction formula, a calibration document 30 in which a plurality of color charts (color patches) 31 are arranged is used. As the proofreading document 30, for example, a Japan Color 2002 print sample composed of 928 color charts can be used. However, this is merely an example, and the number of color charts and color variations of the proofreading document 30 are not limited to this. The size of each color chart needs to be larger than the observation area of the spectroscopic measurement device (not shown). In this case, it is about 10 mm × 10 mm. Further, as the proofreading document 30, a printed matter using area gradation can be used, but not limited to this, a document having density gradation such as a photograph may be used.

  In this embodiment, the read output value of each color chart (color chart ideal output value data 42) when it is assumed that the image reader 50 has read each color chart of the calibration document 30 in an ideal state without crosstalk. Obtain by calculation. Then, the image reading device 50 actually reads the calibration document 30 to obtain the read output value of each color chart affected by the crosstalk, and converts the read output value into the color chart ideal output value data 42. Find the talk correction formula.

  For such calculation, spectral colorimetric data 32 of each color chart of the proofreading document 30 is obtained by spectrally measuring each color chart 31 of the proofreading document 30 with a spectroscopic measurement device.

  The sensor spectral sensitivity data 34 for each color of the CCD sensor included in the image reading device 50 can be obtained from the manufacturer of the CCD sensor. If there is sufficient equipment, the sensor spectral sensitivity data 34 can be obtained by actual measurement.

  Further, the spectral distribution data 36 of the illumination light source for document illumination provided in the image reading apparatus 50 can be obtained by measurement using a spectral radiance meter. Instead of obtaining by measurement in this way, if the spectral distribution data of the illumination light source can be obtained from a light source manufacturer or the like, this may be used. In this case, the illumination light source may be provided with a reflecting plate for deflecting and converging light, and a heat ray absorption filter, and a platen glass is interposed between the light source and the document. The illumination light source spectral distribution data 36 is calculated from various data such as the spectral distribution data of the light source itself, the transmittance of the heat ray absorption filter, and the platen glass.

  The imaging optical system spectral distribution data 38 is a spectral transmittance of an optical system that forms an image of reflected light from a document on a CCD sensor, and a spectral reflectance of a reflection plate disposed on an optical path. From which data is disclosed. In most cases, the imaging optical system spectral distribution data is often flat over the entire visible light band, so that the correction formula can be obtained without this data.

  The color chart ideal output value data calculation unit 40 calculates the color chart ideal output value data using these data 32 to 38. Hereinafter, this calculation method will be described.

Let λ be the wavelength of light. The spectral distribution P (λ) of the illumination light source is obtained from the illumination light source spectral distribution data 36. The spectral sensitivities R (λ), G (λ), and B (λ) of the R, G, and B channels of the CCD sensor are obtained from the sensor spectral sensitivity data 34. The spectral reflectance Ti (λ) of the i-th color chart on the calibration original 30 is obtained from the color chart spectral colorimetric data 32. The spectral distribution L (λ) of the imaging optical system is obtained from the imaging optical system spectral distribution data 38. The color chart ideal output value data calculation unit 40 calculates ideal output value data (Rci, Gci, Bci) of the i-th color chart by the following calculation.

  In this calculation formula, White (Ra), White (Ga), and White (Ba) are output values of the R, G, and B channels when a predetermined white reference plate is read, and this is for normalization. Used for. Further, the summation operation [Sigma] is the summation for each [lambda] where the data 32-38 exist over the entire visible light range. By performing this calculation for all color charts i of the proofreading document 30, ideal output value data (Rci, Gci, Bci) for each color chart i is calculated.

  The color chart ideal output value data obtained in this way can be used in common if the model of the image reading device 50 is the same.

  The above is the configuration and processing method for obtaining the reading output value of the ideal (that is, without crosstalk) color chart of the image reading apparatus 50.

  On the other hand, the color chart actual output value data 54 for each color chart i is obtained by actually reading the calibration document 30 by the image reading apparatus 50. In this process, first, the image reading device 50 is set so that the R, G, B data input by the color space conversion unit 20 shown in FIG. 3 is output as it is. In this state, the calibration original 30 is placed on the platen of the image reading device 50 and read. The image reading device 50 outputs R, G, and B data that has not undergone color space conversion. The color chart actual output value data calculation unit 52 has information on the area of each color chart i on the proofreading document 30 (the area size may be approximately the same as the observation area of the spectroscopic measurement device, for example). From this information, the data of the area of each color chart i in the R, G, B data is obtained, and the value (Rai, Gai, Bai) obtained by averaging the data of the area for each of R, G, B is the color chart. Output as measured output value data 54.

The crosstalk correction formula calculation unit 60 obtains a crosstalk correction matrix A62 that satisfies the relationship expressed by the following formula 2 from the color chart ideal output value data 42 and the color chart actual output value data 54.

  Formula 2 is a linear conversion formula from the color chart actual output value to the color chart ideal output value.

  Here, the correction matrix A is a method of linear multiple regression analysis using the relationship between the actually measured output values (Rai, Gai, Bai) and the corresponding ideal output values (Rci, Gci, Bci). It can be calculated by multiplication.

  FIG. 5 is a graph plotting the relationship between the color chart actual output value and the color chart ideal output value for each color chart i for the B channel of an image reading apparatus 50, with the horizontal axis representing the ideal output value and the vertical axis representing the ideal output value. The measured output value is taken. Although only the B channel is shown in the figure, the same relationship is obtained for R and G, and the correction matrix A is obtained by performing linear multiple regression analysis on these relationships.

  The result of applying this correction matrix A to the actual measurement data of each color chart i is shown in FIG. As can be seen from this figure, by using the correction matrix A, it is possible to reduce the variation in the correlation between the actually measured output value and the ideal output value.

  Formula 2 incorporating the crosstalk correction matrix A obtained as described above is a crosstalk correction formula. By incorporating this correction-type arithmetic processing into the image reading apparatus 50, crosstalk correction at the time of document reading can be realized. Hereinafter, with respect to the crosstalk correction, two implementation methods and examples of correction processing for each of them will be described.

  As shown in the example of FIG. 3, in the image reading device 50, multiplication processing is performed on all pixel data by the shading correction units 16 R, 16 G, and 16 B and the color space conversion unit 20. The crosstalk correction method of the present embodiment can be incorporated in the arithmetic processing of the shading correction units 16R, 16G, 16B or the color space conversion unit 20.

  First, a first method for incorporating crosstalk correction into color space conversion will be described.

The line gap correction unit 18 in FIG. 3 performs gap correction by delaying and outputting a signal by a time corresponding to the gap between the R, G, and B channels of the CCD sensor. More specifically, when an image is read with the color linear CCD sensor 10 arranged as shown in FIG. 2, the output after the line gap correction corresponding to the t-th line of the document (R ′ (t), G ′ (t), B ′ (t)) is the following for the signals (r (t), g (t), b (t)) of the R, G, B channels before the line gap correction. It becomes such a relationship.
R ′ (t) = r (t−2N)
G '(t) = g (tN)
B '(t) = b (t)
Where N is the size of the line gap (unit is the number of lines in the sub-scanning direction)

  This is an expression in the case where crosstalk correction is not performed. FIG. 7 shows the relationship of signal output from the line gap correction unit 18 to the color space conversion unit 20 in this case. This figure is a diagram when the line gap size N is 4. FIG.

  When performing crosstalk correction, it is necessary to consider the influence of crosstalk of other channels in order to obtain the value of a certain channel. Here, since the signal of each channel at the same time affects other channels in crosstalk, it is necessary to use the signal of each channel at the same time for the correction calculation. That is, the R channel and G channel signals on the t-th line of the document must be obtained from the signals of the respective channels at the time 2N and 1N lines before the B channel signal, respectively.

ここで、Ａは前述のクロストーク補正マトリックスである。
この式を展開すると次の式になる。

This is expressed by the following expression 3.

Here, A is the aforementioned crosstalk correction matrix.
When this expression is expanded, the following expression is obtained.

  The color space conversion unit 20 performs conversion from a device-dependent color space such as RGB into a device-independent color space such as CIEL * a * b * by performing a matrix operation on the data after line gap correction. .

In this color space conversion, a matrix operation with a non-linear term added is performed in order to correct the deviation between the spectral sensitivity of the image reading device 50 and the color matching function used for calculating CIEL * a * b * and the like. For example, not only RGB linear terms as shown in the following equation 5, but also a 3 × 9 matrix operation in which square terms and integration terms are added is used.

  This matrix operation is a conventionally known one. The color space conversion unit 20 in the case where the crosstalk correction shown in FIG. 7 is not performed performs the color space conversion using Equation 5 as it is.

  In contrast, in the present embodiment in which crosstalk correction is incorporated into color space conversion, the 3 × 9 matrix arithmetic expression of Expression 5 is modified and used. In calculating the color space matrix, it has been confirmed that the contribution rate of the nonlinear term is extremely low compared to the linear term. Therefore, the calculation of the nonlinear term and the correlation is omitted, and an equation using the linear term of the RGB value of the target pixel and the linear terms of the RGB values before the N line and 2N lines before is used.

The color space conversion expression when only the linear terms of input RGB are extracted from Expression 5 is Expression 6 below.

The following equation 7 is obtained by combining the calculation by the crosstalk correction matrix A of equation 3 with this.

  By executing the calculation of Equation 7, crosstalk correction and color space conversion can be realized simultaneously. FIG. 8 shows the relationship of signal input from the line gap correction unit 18 to the color space conversion / crosstalk correction calculation unit 22 that executes the calculation of Expression 7. FIG. 8 corresponds to FIG. 7 and shows a case where the size N of the line gap is 4. Further, FIG. 9 shows a configuration of an image reading apparatus 50 provided with the color space conversion / crosstalk correction calculation unit 22. The color space conversion / crosstalk correction calculation unit 22 only needs to be able to execute the calculation of Expression 7, and can be realized by software processing, a hardware circuit such as an ASIC, or a DSP (digital signal processor).

  With such a configuration, it is possible to perform the crosstalk correction calculation in real time without greatly changing the configuration of the image processing circuit of the existing image reading device 50.

  Next, a second method for incorporating the crosstalk correction into the shading correction calculation will be described. FIG. 10 is a block diagram of an image reading apparatus 50 of this type.

  As described above, the crosstalk correction of the present embodiment is based on the precondition that the calculation using the correction equation is performed on the signals of the RGB channels captured at the same timing in time.

  In the above-described method in which crosstalk correction is incorporated in color space conversion, crosstalk correction is performed by the color space conversion / crosstalk correction unit 22 after line gap correction. It was. On the other hand, in the shading correction before the line gap correction process, the R, G, and B signals input from the upstream are at the same time. Therefore, the method of incorporating the crosstalk correction in the shading correction simplifies the calculation process. Become.

ここで、CoefＲi等及びOffsetＲ等は、それぞれシェーディング補正の補正係数及びオフセット値である。 That is, if the value of each i-th RGB pixel on the line in the main scanning direction is (ri, gi, bi), the values after shading correction (r'i, g'i, b'i) are It is expressed by the following formula.

Here, CoefRi and the like and OffsetR and the like are a correction coefficient and an offset value for shading correction, respectively.

ここで、ａ_ｒｒ〜ａ_ｂｂは、式２のクロストーク補正マトリックスＡの各要素の値である。 Both the crosstalk correction and the shading correction can be executed by applying the calculation by the crosstalk correction matrix A obtained by the expression 3 to the input signal (ri, gi, bi) in the expression 8. The arithmetic expression at this time is the following Expression 9.

Here, a _{rr to} a _bb are values of each element of the crosstalk correction matrix A of Equation 2.

  The configuration of the image reading device 50 according to this method is shown in FIG. In the apparatus of FIG. 10, the crosstalk correction is executed simultaneously with the shading correction by the shading / crosstalk correction units 17R, 17G, and 17B for each of the RGB channels. Since signals of other channels are required for crosstalk correction, all the RGB signals are input to the shading / crosstalk correction units 17R, 17G, and 17B. This is different from the configuration of the conventional apparatus shown in FIG. The components other than the input wiring from the shading / crosstalk correction units 17R, 17G, and 17B and the A / D converters 14R, 14G, and 14B may be the same as those in FIG. The shading / crosstalk correction units 17R, 17G, and 17B only need to be able to execute the calculation of Expression 9, and can be realized by software processing, a hardware circuit such as an ASIC, or a DSP (digital signal processor).

  As described above, even when the crosstalk correction is incorporated in the shading correction, the crosstalk correction calculation can be performed in real time without greatly changing the image processing configuration of the existing image reading apparatus.

FIG. 11 shows a graph of RGB output after crosstalk correction of the image reading device 50 according to the present embodiment. This is common to the above-described first method and second method. However, the first method is a case where the coefficients of the linear terms C _{11 to} C ₃₃ of the color space conversion matrix are set to 1.0. Various conditions such as a manuscript are the same as in the graph (FIG. 1) when crosstalk occurs. As can be seen from a comparison between FIG. 11 and FIG. 1, the effect of the crosstalk is improved by the correction effect of the present embodiment, and as a result, the drop of the B signal in the sudden change portion from black to white is eliminated. I understand.

  In the above embodiment, the CCD sensor outputs RGB color signals, but the system of the embodiment can be applied to sensors that output color signals in other color spaces. In the above-described embodiment, the conversion to the CIE L * a * b * color space is performed. However, the above method can be applied to the conversion to a color space other than this. Of course, the color chart 31 group may be divided into a plurality of proofreading documents 30 and arranged.

It is the figure which showed the mode of crosstalk generation | occurrence | production in the graph. It is the figure which showed the structure of a general color linear CCD sensor, and the image reading conditions in calculating | requiring the graph of FIG. It is the figure which showed the structure for signal processing of a general image reading apparatus. It is the figure which showed the system configuration | structure for the crosstalk correction matrix calculation process of embodiment. It is the graph which showed the correlation with the color chart ideal output value data used for calculation of a crosstalk correction matrix, and a color chart actual output value. It is the graph which showed the correlation of the output value which applied the crosstalk correction matrix, and color chart ideal output value data. It is the figure which showed the signal input / output relationship between the line gap correction | amendment part and color space conversion part in a general image reading apparatus. It is the figure which showed the signal input / output relationship between the line gap correction | amendment part and a color space conversion and crosstalk correction calculating part in the 1st system which incorporates crosstalk correction | amendment in color space conversion. It is the figure which showed the structure for signal processing of the image reader of a 1st system. It is the figure which showed the structure for signal processing in the 2nd system which incorporates crosstalk correction in shading correction. It is a graph which shows the effect of crosstalk amendment by an embodiment.

Explanation of symbols

  10 color linear CCD sensor, 12R, 12G, 12B analog amplifier, 14R, 14G, 14B A / D converter, 16R, 16G, 16B shading correction unit, 17R, 17G, 17B shading crosstalk correction unit, 18 line gap Correction unit, 19 buffer, 20 color space conversion unit, 22 color space conversion / crosstalk correction calculation unit.

Claims (5)

A method of calculating a correction formula for correcting crosstalk between colors in an image reading apparatus that detects and reads light from a document by each light receiving unit for each color,
Based on the spectral reflectance data of a plurality of color charts for which spectral reflectance is measured and the spectral sensitivity characteristic data for each color of the image reading apparatus, the image reading apparatus uses the intercolor crosstalk between the color charts. A step of obtaining ideal output value data when it is assumed that the reading is performed in an ideal state without,
The actual reading of each color chart by the image reading device to obtain the measured output value data of each color chart;
Obtaining a correction formula for inter-color crosstalk so that the difference between the ideal output value data and the actually measured output value data is minimized across the plurality of color charts;
A method for calculating a crosstalk correction formula between colors. The intercolor crosstalk correction formula calculation method according to claim 1,
Spectral sensitivity characteristic data for each color of the image reading device includes spectral sensitivity data of the light receiving portion of each color, spectral distribution data of a light source for document illumination included in the image reading device, and the image reading device. Spectral distribution data of the image optical system,
A method for calculating a crosstalk correction formula between colors. An image reading device that detects and reads light from a document by each light receiving unit for each color,
A crosstalk correction calculation unit that performs an intercolor crosstalk correction calculation on an image signal obtained by reading a document,
The crosstalk correction calculation unit includes ideal output value data when it is assumed that the image reading device has read a plurality of color charts whose spectral reflectances are measured in an ideal state without intercolor crosstalk, and the plurality of color charts. The image signal is calculated using an inter-color crosstalk correction formula so that a difference between the color chart and the actually measured output value data actually obtained by the image reading apparatus is minimized in the plurality of color charts. Intercolor crosstalk correction calculation is performed on
An image reading apparatus. The image reading apparatus according to claim 3,
The crosstalk correction calculation unit includes a color space conversion calculation for converting the signal of each color detected by the light receiving unit into a signal of a predetermined color space, a calculation of the correction formula for the intercolor crosstalk, By performing an operation that combines, color space conversion processing and crosstalk correction processing are performed simultaneously.
An image reading apparatus. The image reading apparatus according to claim 3,
The crosstalk correction calculation unit performs a shading correction process by combining a shading correction calculation for the signals of each color detected by the light receiving unit and a calculation of the correction formula for the intercolor crosstalk, Perform crosstalk correction processing at the same time.
An image reading apparatus.

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