JP5393445B2 - Image processing apparatus, image processing method, and computer program - Google Patents

Description

  The present invention corrects color misregistration occurring in color image data.

  An image forming apparatus that reads a document image and forms a color image, such as a color copying machine or a color multifunction peripheral, includes an image scanner unit that reads an image and a printer unit that prints an image read by the image scanner unit. Further, when a document is read as electronic image data by a personal computer or the like, an image scanner device is widely used. In general, a line sensor (read sensor) such as a charge coupled device (CCD) or a contact image sensor (CIS) is used as the image scanner unit or the image scanner device. In the line sensor, a plurality of light receiving elements (photoelectric conversion elements that accumulate incident light and convert it into electric signals) are arranged in a straight line. An original image is read by the line sensor while moving the line sensor in a direction (sub-scanning direction) perpendicular to the arrangement direction (main scanning direction) of the light receiving elements. There is also a configuration in which the line sensor is fixed and the document image is read by the line sensor while moving the document in the sub-scanning direction.

However, if the original image is read while moving the line sensor or the original, the color image data may be misaligned due to the mechanical vibration generated in the drive mechanism that moves the line sensor or the original in the sub-scanning direction or the influence of the feeding accuracy. There was a problem that it occurred. In particular, while moving the line sensor, light sources of at least three colors, for example, R (red), G (green), and B (blue) light sources are sequentially emitted, and a document image is read with the light of each color. The sequential reading method has the following problems. That is, in this line sequential reading method, the line sensor and the read original are normally moved continuously during reading of the original image. Therefore, since the reading position at the light emission timing of each color of R, G, and B is shifted in the sub-scanning direction as described above, color deviation occurs when a document such as a character or a line drawing is read, and the image quality is deteriorated. It was.
In addition, for example, a sensor that covers the main scanning direction is prepared for each color of R (red), G (green), and B (blue), and they are arranged while being shifted in the sub-scanning direction to simultaneously read each color. However, color misregistration occurs due to fluctuations in the moving speed in the sub-scanning direction. This is because image data read at a certain time has a different sensor position for each color, so that the position in the sub-scanning direction needs to be corrected according to the moving speed in the sub-scanning direction and the sensor interval. However, since the reading position assumed by the movement speed fluctuation in the sub-scanning direction is shifted from the actual reading position, color misregistration occurs.

In order to correct (reduce) this color shift, various image processing methods have been proposed. As one of them, by replacing the image data of each reading line with a weighted average of the image data of the reading line and the image data of the reading line of the same color immediately before or immediately after the reading line, A method for correcting the shift is known. In this kind of image processing method, in order to further improve the positional accuracy of R, G, B of each line after averaging, for example, when R is used as a reference, the emission order of G and B is changed every time ( R, G, B, R, B, G, R, G, B... In this order) (see Patent Document 1).
Also, in the sub-scanning direction, image data is read at a resolution twice that at the time of actual output, and thinning is performed after taking a weighted average of the image data of the read line and the image data of the line immediately before and after the read line. Some perform processing (see Patent Document 2). In addition, there is an apparatus that converts image information read in each emission color into luminance information and color difference information, and performs spatial frequency band limitation only on the color difference information to reduce color shift while maintaining a sense of resolution. (See Patent Document 3). In addition, after the image information is converted into luminance information and saturation information, the target pixel is determined when the target pixel is determined to be an achromatic color from the saturation information in the vicinity of the lowest luminance pixel in the vicinity of each target pixel. Is replaced with an achromatic color and replaced with a clear black image (see Patent Document 4).

JP 2000-224375 A JP 2002-142122 A JP-A-4-11458 JP 2003-259135 A

However, in the technique described in Patent Document 1, as described above, the image data of each reading line is obtained by combining the image data of the reading line and the image data of the reading line in the same color immediately before or after the reading line. Replace with weighted average. Therefore, the basic performance of image resolution deteriorates, which is not preferable. In addition, as a result of the weighted average process, the degree of color shift is reduced, but it is not always sufficient.
Further, in the technique described in Patent Document 2, degradation in resolution can be avoided, but the number of pixel data to be processed is doubled when the reading resolution is doubled. That is, if the operation speed of the color misregistration correction circuit is the same, twice the reading time is required. Of course, if the operation speed of the color misregistration correction circuit is increased by a factor of 2, it is possible to avoid resolution degradation without extending the reading time. However, this is not preferable because it is an expensive device for realizing a circuit configuration that operates at high speed.

Further, the technique described in Patent Document 3 has little influence on resolution, reading time, and cost. However, since the color misregistration is only reduced by spatial frequency band limitation, the effect of reducing the color misregistration cannot always be obtained sufficiently.
The technique described in Patent Document 4 is effective for black characters, but no processing is performed for color misregistration in the outline of color characters, color misregistration of black characters in the background of chromatic colors, and the like. Not.
The present invention has been made in view of such problems, and an object of the present invention is to easily and reliably correct color misregistration occurring in color image data.

  The image processing apparatus of the present invention includes an acquisition unit that acquires image data for each line detected by a line sensor configured by arranging a plurality of line-shaped sensors for each color component in the sub-scanning direction; Displacement image data for each color component that is displaced in the sub-scanning direction by the amount of displacement set for each color component with respect to the image data of the color component that is different from the reference color component among the line image data A synthesizer for synthesizing displacement image data for each color component acquired by the displacing unit, and generating synthesized color data corresponding to the reference color component; Deriving means for deriving the correlation between the generated composite color data and the image data of the reference color component, and the composite color data having the highest correlation between the image data of the reference color component It characterized in that it has a selection means for selecting a response to displacement image data.

  According to the present invention, displacement image data for each color component, which is displaced in the sub-scanning direction by a displacement amount set for each color component with respect to image data having a color component different from a reference color component, is obtained. The synthesized color data corresponding to the reference color component is generated by the synthesis. Then, the displacement image data corresponding to the composite color data having the highest correlation with the image data of the reference color component is selected. Accordingly, it is possible to select appropriate displacement image data without performing complicated processing. Therefore, color misregistration that occurs in the color image data can be reliably reduced without using a complicated configuration or increasing the processing time.

It is a figure which shows the main structures of the image reading part which concerns on 1st Embodiment. FIG. 4 is a diagram illustrating a positional relationship of a color image sensor with respect to a document. It is a figure explaining the structure of an image processing apparatus. It is the figure which expanded and showed the color image sensor vicinity. It is a figure explaining the structure of the image processing apparatus which concerns on 2nd Embodiment. It is a figure which shows the relationship between the frequency | count of repetition, and displacement amount difference value. 10 is a flowchart for explaining the operation of the image processing apparatus according to the third embodiment.

(First embodiment)
Hereinafter, the first embodiment will be described with reference to the drawings.
FIG. 1 is a cross-sectional view illustrating an example of a main structure of an image reading unit in an image processing apparatus. A document 201 to be read is transported by a document transport roller 202 and sent to a discharge document receiver (not shown) via a document discharge member 203. A black and white sensor 204a, a green sensor 204b, a red sensor 204c, and a blue sensor 204d are provided between the document conveying roller 202 and the document discharge member 203, and a color image sensor 204 for reading the corresponding color component amount. is there. As described above, the color image sensor 204 is a line sensor including a plurality of individual line sensors for each color component.
FIG. 2 is a plan view showing an example of the positional relationship of the color image sensor 204 with respect to the document 201. The sub-scanning direction is opposite to the document conveyance direction in FIG.
As is clear from FIG. 2, at a certain point in time, the monochrome sensor 204a, the green sensor 204b, the red sensor 204c, and the blue sensor 204d each read a different position in the sub-scanning direction on the document 201. For this reason, it is necessary to correct the shift in the sub-scanning direction. Conventionally, a color shift in the sub-scanning direction due to a difference in sensor position has been corrected by using a buffer having a different delay amount for each color according to the difference in sensor position in the sub-scanning direction and the document conveyance speed.

However, in FIG. 1, when the leading edge of the document 201 reaches the document discharge member 203, the document conveyance speed may be reduced due to the impact of the collision. Further, when the end of the document 201 tries to leave the document transport roller 202, the document transport speed may increase due to the elasticity of the document transport roller 202. Conventionally, the delay amount of the buffer for each color is not changed in accordance with the document conveyance speed. Therefore, when the document conveyance speed is changed from the standard speed, correction of color misregistration in the sub-scanning direction does not function well.
FIG. 3 is a block diagram illustrating an example of the configuration of the image processing apparatus in a portion that performs color misregistration correction processing in the sub-scanning direction. In the portion shown in FIG. 3, the image data read by the color image sensor 204 is sequentially processed to obtain output image data in which color misregistration in the sub-scanning direction is corrected. In the present embodiment, the monochrome image data corresponding to the monochrome sensor 204a out of the four color image data read by the color image sensor 204 is used as a reference. Then, based on this black and white image data, the color shift in the sub-scanning direction of the green image data, red image data, and blue image data corresponding to each of the green sensor 204b, the red sensor 204c, and the blue sensor 204d is corrected. .

First, the outline of each part in FIG. 3 will be described.
The sub-scanning direction displacement processing units 101 to 103 respectively input green image data, red image data, and blue image data, and displace the input green image data, red image data, and blue image data in the sub-scanning direction. To generate displacement image data of each color. The color composition processing units 104 to 106 generate composite brightness data from the displacement image data of each color obtained by the sub-scanning direction displacement processing units 101 to 103, respectively. Correlation degree calculation processing sections 108 to 110 derive correlation degrees indicating how much the combined lightness data obtained by the color composition processing sections 104 to 106 matches the monochrome image data obtained by the monochrome sensor 204a.
The delay buffers 111 to 113 respectively end the processing of the displacement image data of each color obtained by the sub-scanning direction displacement processing units 101 to 103 by the correlation degree calculation processing units 108 to 110 and input the image data selection unit 114. This is to synchronize the output. The image data selection unit 114 selects the displacement image data having the highest degree of correlation obtained by the correlation degree calculation processing units 108 to 110 from the displacement image data from the delay buffers 111 to 113. The displacement amount control unit 115 controls (changes) the amount of change of each color in the sub-scanning direction displacement processing units 101 to 103 based on the selection information from the image data selection unit 114.

Details of each part will be described below.
FIG. 4 is an enlarged view showing the vicinity of the color image sensor 204 of FIG. Here, as shown in FIG. 4, the sensor reading pitch (the size of one pixel in the image data) corresponding to the resolution in the sub-scanning direction is “1”. Further, as the position of the green sensor 204b based on the position of the monochrome sensor 204a, the sensor interval (monochrome / green) in FIG. 4 is set to “3”. The sensor interval here is the length from the base end of the monochrome sensor 204a in the sub-scanning direction to the base end of the corresponding sensor in the sub-scanning direction. Similarly, it is assumed that the sensor intervals of the red sensor 204c and the blue sensor 204d are “6” and “9”, respectively.
Here, the standard document conveyance speed is “1”. In other words, the sensor reading pitch length “1” is read at time “1”. At a standard document conveyance speed, the time from when a point on the document 201 passes over the green sensor 204b until it passes over the monochrome sensor 204a is “3” as the sensor interval (black and white). Since the conveyance speed is “1”, “3” (= 3 ÷ 1). Therefore, the image data read by the green sensor 204b precedes the image data read by the monochrome sensor 204a by time “3”. Since the time “3” is 3 pixels in the image data, in order to synchronize the image data with the monochrome sensor 204a as a reference, the image data read by the green sensor 204b can be delayed by 3 pixels in the sub-scanning direction. It ’s fine.

Here, consider a case where the document conveyance speed is increased from “1” to “1.5”. Then, as for the time from when a certain point of the document 201 passes over the green sensor 204b until it passes over the monochrome sensor 204a, the sensor interval (black and white / green) is “3” and the document transport speed is “1”. .5 ”, so“ 2 ”(= 3 ÷ 1.5). In this case, since the time “2” is for two pixels in the image data, in order to synchronize the image data based on the monochrome sensor 204a, the image data read by the green sensor 204b is equivalent to two pixels in the sub-scanning direction. You can delay it.
In this embodiment, instead of measuring the document conveyance speed, the color misregistration is corrected by selecting the one that maximizes the correlation between the redundant color components. That is, the combined brightness data calculated based on the green image data, red image data, and blue image data obtained by the green sensor 204b, the red sensor 204c, and the blue sensor 204d, and the monochrome image data obtained by the monochrome sensor 204a. The document conveyance speed is indirectly estimated by the correlation.

In the initial state, the displacement amount control unit 115 causes the sub-scanning direction displacement processing unit 102 to perform a displacement amount corresponding to the standard document conveyance speed (= “1”) (in the above example, the green image data). “3”, “6” for red image data, and “9” for blue image data. For the sub-scanning direction displacement processing unit 101, a displacement amount is set assuming that the document conveyance speed is slightly reduced to “0.8”. For the sub-scanning direction displacement processing unit 103, a displacement amount is set assuming that the document conveyance speed is slightly increased to “1.2”.
In calculating the amount of displacement set for the sub-scanning direction displacement processing unit 101, the value obtained by dividing “3”, which is the sensor interval (monochrome / green), by “0.8” with respect to the green image data. “3.75” can also be set. However, it is assumed that the standard document conveyance speed is “1” until time t−1 with respect to the current time t, and then decreases to “0.8” as “3.25” (= 2 + 1 / 0.8). It is better to set.
Therefore, here, the latter is adopted, and the sub-scanning direction displacement processing unit 101 sets “3.25” as the sensor interval for the green image data, “6.25” as the sensor interval for the red image data, and blue image data. Assume that “9.25” is set as the sensor interval for.

In the present embodiment, the sub-scanning direction displacement processing unit 101 obtains displacement image data corresponding to a delay amount of “3.25” that is a sensor interval with respect to green image data as follows. That is, the sub-scanning direction displacement processing unit 101 calculates the displacement image data corresponding to the delay amount of “3.25” by the weighted average of the image data delayed by 3 pixels in the sub-scanning direction and the image data delayed by 4 pixels. Ask for. For red image data and blue image data, displacement image data is obtained in the same manner as the green image data.
Similarly to the sub-scanning direction displacement processing unit 101, the sub-scanning direction displacement processing units 102 and 103 also obtain displacement image data of each color based on the delay amount set by the displacement amount control unit 115.

The color composition processing units 104 to 106 use the displacement image data obtained by the sub-scanning direction displacement processing units 101 to 103 according to the sensor characteristics of the monochrome sensor 204a, the green sensor 204b, the red sensor 204c, and the blue sensor 204d. Obtain composite brightness data. In the present embodiment, since the monochrome image data is used as the reference image data, the combined lightness data corresponding to the monochrome component is obtained by combining the green component, the red component, and the blue component.
Here, it is assumed that the combined lightness (Y) is obtained from the green component (G), the red component (R), and the blue component (B) for each pixel according to the following equation (1).
Y = 0.29891 x R + 0.58661 x G + 0.11448 x B (1)
Correlation degree calculation processing units 108 to 110 compare the combined lightness data obtained by the color composition processing units 104 to 106 and the black and white image data obtained by the black and white sensor 204a, and determine which of them is It is for obtaining a numerical value that serves as an index whether the degree is consistent. As such an index, for example, a correlation coefficient, a sum of absolute differences, and a sum of squared differences are known. Here, the sum of absolute differences is adopted in consideration of the implementation cost.

The delay buffers 111 to 113 hold the displacement image data obtained by the sub-scanning direction displacement processing units 101 to 103 until the calculation of the sum of absolute differences is completed by the correlation degree calculation processing units 108 to 110, respectively. Is for.
The image data selection unit 114 is for selecting, as an output, displacement image data corresponding to the one having the smallest difference absolute value sum by the correlation degree calculation processing units 108 to 110. For example, if the difference absolute value sum by the correlation degree calculation processing unit 108 is the minimum, the image data selection unit 114 selects the displacement image data stored in the delay buffer 111 corresponding to the correlation degree calculation processing unit 108. . Further, the image data selection unit 114 transmits information indicating which displacement image data is selected to the displacement amount control unit 115 as information for the displacement amount control unit 115 to calculate the subsequent displacement amount. For example, assuming that the sum of absolute differences by the correlation degree calculation processing unit 108 is minimum, the displacement amount control unit 115 estimates that the document conveyance speed is slightly reduced to “0.8” at time t. Then, the displacement amount control unit 115 sets “0.8”, which is the latest document conveyance speed information, as the standard document conveyance speed as the displacement amount to be set for the sub-scanning direction displacement processing unit 102 next. A displacement amount corresponding to the document conveyance speed is set. Further, the displacement amount control unit 115 sets a displacement amount assuming that the document conveyance speed further decreases to “0.6” with respect to the sub-scanning direction displacement processing unit 101. Further, the displacement amount control unit 115 sets a displacement amount assuming that the document conveyance speed is restored to “1.0” with respect to the sub-scanning direction displacement processing unit 103.

As described above, in this embodiment, the sub-scanning direction displacement processing units 101 to 103 register three candidates as displacement amounts in the sub-scanning direction based on the setting from the displacement amount control unit 115. The sub-scanning direction displacement processing units 101 to 103 generate displacement image data by shifting the green image data, red image data, and blue image data in the sub-scanning direction by the registered displacement amount. The color synthesis processing units 104 to 106 combine the green component, red component, and blue component of the displacement image data generated by the sub-scanning direction displacement processing units 101 to 103 to generate combined brightness data corresponding to the monochrome component. Correlation degree calculation processing units 108 to 110 check the correlation between the combined brightness data generated by the color synthesis processing units 104 to 106 and the monochrome image data, and the image data selection unit 114 has the highest correlation with the monochrome image data. Displacement image data corresponding to high composite brightness data is selected and output. The displacement amount control unit 115 changes the displacement amount set in the sub-scanning direction displacement processing units 101 to 103 based on the displacement amount in the displacement image data selected by the image data selection unit 114.
Therefore, even when the document conveyance speed changes, the displacement amount of each component can be changed independently according to the reference color component, and a relatively small circuit or a relatively short software can be used. A good color misregistration correction result can be obtained in the processing time. Further, for example, regardless of the color of a character, the color shift generated in the contour portion is corrected, and a clear image in which the color shift of the contour portion is corrected is output even when the background color is other than white. Can do.

In the example described above, as shown in FIGS. 1, 2, and 4, the arrangement order of the sensors starts from the one closest to the reference black and white sensor 204 a in descending order of the coefficients in the color composition processing units 104 to 106, that is, , Green sensor 204b, red sensor 204c, and blue sensor 204d. This is because the blue component having a small coefficient in the color composition processing units 104 to 106 has a small influence on the combined brightness data, and therefore increases the detection sensitivity of the speed fluctuation by taking the distance from the reference monochrome sensor 204a.
As another method for arranging the sensors, it is conceivable to use visual sensitivity as a reference. For example, when determining the order in which the complementary colors of cyan, magenta, and yellow are arranged in the reference color black, the yellow sensor that is difficult to visually recognize is preferably arranged near the black sensor that is the reference color. . This is because if the distance from the reference color sensor is small, the sensitivity of detecting the speed fluctuation is deteriorated, but the color is difficult to be visually recognized, so the influence on the image quality is not so great.
As described above, for example, the color component sensor having a higher correlation with the reference color component is disposed closer to the reference sensor (black and white sensor 204a), or the sensor having a higher lightness is used. It can be arranged at a position close to the reference sensor.

  In the above-described example, as shown in FIG. 2, the color image sensor 204 (the monochrome sensor 204a, the green sensor 204b, the red sensor 204c, and the blue sensor 204d) is fixed, and the document 201 is moved while being moved. To read. However, as another configuration example, the color image sensor 204 can be moved while the document 201 is fixed. In this case, when the movement of the color image sensor 204 is started and stopped, the driving load increases due to inertia, and it is difficult to move the color image sensor 204 at a constant speed. Therefore, as in the example described so far, the moving speed in the sub-scanning direction fluctuates and color misregistration occurs. However, even with such a configuration, if the original 201 and the color image sensor 204 are considered relative to each other, the color image sensor 204 moves in the sub-scanning direction and the moving speed varies, so that color misregistration occurs. It is common to generate. Therefore, the present embodiment is also applicable to the case where the color image sensor 204 is moved while the document 201 is fixed as described above.

The color combination of the color image sensor 204 is not limited to black and white, green, red, and blue. For example, four colors of cyan (C), magenta (M), green (G), and red (R) may be used. Considering the three primary colors cyan, magenta, and yellow, green has cyan and yellow components, and red has magenta and yellow components. For example, composite color data (G *) corresponding to green can be obtained by the following equation (2).
G * = a * Cb * M + c * R (2)
After correcting the color misregistration as described above, if the yellow component is calculated from magenta and red, color image data using the three complementary primary colors can be obtained.
Further, the number of candidates to be registered as the displacement amount is not limited to “3”.

  As described above, when the leading edge of the document 201 reaches the document discharge member 203, the document conveyance speed may be reduced due to the impact of the collision. Further, when the end of the document 201 tries to leave the document transport roller 202, the document transport speed may increase due to the elasticity of the document transport roller 202. The displacement amount control unit 115 can determine the displacement amount to be set in the sub-scanning direction displacement processing units 101 to 103 in consideration of such characteristics due to the sub-scanning position. That is, for image data read by the color image sensor 204 around the time when the leading edge of the document 201 reaches the document discharge member 203, there is a high possibility that the document conveyance speed is below the standard. Assuming that the number of candidates for the displacement amount is 3 as in the above example, the speeds of “0.8”, “1.0”, and “1.2” are assumed under normal circumstances. At the assumed position, the amount of displacement is set assuming the case of “0.6” instead of the speed “1.2”. Similarly, for the image data read by the color image sensor 204 before and after the time when the end of the document 201 is about to leave the document transport roller 202, the document transport speed is higher than the standard, assuming an increase in the document transport speed. The amount of displacement corresponding to is set more than usual.

(Second Embodiment)
Hereinafter, the second embodiment will be described. In the first embodiment described above, the sub-scanning direction displacement processing units 101 to 103, the color composition processing units 104 to 106, the correlation calculation processing units 108 to 110, and the delay buffers 111 to 113 are separately prepared, and the color composition processing is performed. In addition, a plurality of correlation degree calculation processes are processed in parallel. In contrast, in the present embodiment, color misregistration correction is performed without performing such parallel processing. As described above, the present embodiment is different from the first embodiment described above mainly in part of the processing when performing color misregistration correction. Therefore, in the description of the present embodiment, the same parts as those in the first embodiment described above are denoted by the same reference numerals as those in FIGS.

FIG. 5 is a block diagram illustrating an example of the configuration of the image processing apparatus in a portion that performs color misregistration correction processing in the sub-scanning direction.
In the present embodiment, it is assumed that image data of four colors acquired by the color image sensor 204 in FIG. 1 is stored in the input image memory 503 in advance. Then, color misregistration correction processing in the sub-scanning direction is performed on these four color image data and stored in the output image memory 509. Three of the four colors are color image data to be corrected for color misregistration, and one color is reference image data that serves as a reference for the position in the sub-scanning direction. In the present embodiment, the single color composition processing unit 505 and the correlation degree computation processing unit 506 are used to calculate the degree of correlation between the combined lightness data and the reference image data in different amounts of displacement in a time-sharing manner.

First, the outline of each part in FIG. 5 will be described.
The processing target line selection unit 501 determines which line of the reference image data in the input image memory 503 is to be processed. The displacement amount control unit 502 temporarily calculates a displacement amount in the sub-scanning direction for each color component of the color image data in the input image memory 503. The input image memory 503 is for holding image data to be processed. The sub-scanning direction displacement processing unit 504 obtains displacement image data displaced in the sub-scanning direction by the displacement amount set by the displacement amount control unit 502 for each color component of the color image data in the input image memory 503. The color composition processing unit 505 obtains composite color data corresponding to a color serving as a reference for the sub-scanning position among the four colors in the input image memory 503 by combining each color component of the color image data.

  The correlation degree calculation processing unit 506 calculates the degree of correlation between the combined color data generated by the color combination processing unit 505 and the image data of the color component serving as a reference for the sub-scanning position. The maximum correlation degree determination unit 507 has combined color data that maximizes the degree of correlation with the image data of the color component serving as the reference for the sub-scanning position in the line selected by the processing target line selection unit 501. The amount of displacement in the sub-scanning direction corresponding to and the degree of correlation are held. The sub-scanning direction displacement processing unit 508 performs sub-scanning on image data in the input image memory 503 using the displacement amount in the sub-scanning direction, which is held by the maximum correlation degree determination unit 507 and has the maximum degree of correlation. Displacement image data in which the color shift in the direction is corrected is obtained. The output image memory 509 is for holding image data that has been subjected to color misregistration correction processing in the sub-scanning direction.

Details of each part will be described below.
The processing target line selection unit 501 determines which line is to be processed with respect to the reference image data in the input image memory 503, and notifies each unit of a target line number for identifying the target line. The following units, that is, the displacement amount control unit 502, the correlation degree calculation processing unit 506, and the sub-scanning direction displacement processing units 504 and 508 perform processing with reference to the target line number. When the predetermined condition is satisfied (in this embodiment, when the process for the same target line number is repeated a predetermined number of times, or when the maximum correlation degree determination unit 507 causes the correlation to exceed the predetermined threshold When the degree is obtained), a new attention line is selected. In the present embodiment, it is assumed that the processing target line selection unit 501 sequentially selects the target line from the first line in the sub-scanning direction of the processing target image data.

The displacement amount control unit 502 determines the displacement amount of the image data of each color component in the line of the target line number selected by the processing target line selection unit 501. The displacement amount control unit 502 has a repetition number counter that indicates the number of times the displacement amount is instructed to the sub-scanning direction displacement processing unit 504 for a certain line number of interest, and the displacement amount is determined according to the value of the repetition number counter. decide. When the target line number selected by the processing target line selection unit 501 is different from the target line number specified immediately before, the displacement amount control unit 502 resets the repetition count counter to “0”. On the other hand, when the target line number selected by the processing target line selection unit 501 is the same as the target line number specified immediately before, the displacement amount control unit 502 adds “1” to the repeat count counter.
FIG. 6 is a diagram illustrating an example of the relationship between the number of times the displacement amount is instructed to the sub-scanning direction displacement processing unit 504 (the number of repetitions) and the displacement amount difference value.

  For example, the displacement amount control unit 502 holds the table shown in FIG. 6, converts the value of the repetition counter to the displacement amount difference value in the sub-scanning direction according to this table, and converts the displacement amount difference value into the displacement amount by color. The amount of displacement is determined by adding the amount reference value. The displacement amount reference value may be a predetermined value determined for each color, for example, a displacement amount in the sub-scanning direction assuming a standard document conveyance speed. Further, when the processing of a certain line is finished, the displacement amount corresponding to the combined color data having the maximum degree of correlation in that line may be used as the displacement amount reference value in the subsequent line processing. Further, the document conveyance speed is reduced when the leading edge of the document 201 reaches the document discharge member 203, and the document conveyance speed is increased when the end of the document 201 tries to leave the document conveyance roller 202. The displacement reference value may be determined according to the target line number.

  The sub-scanning direction displacement processing unit 504 stores the image stored in the input image memory 503 in accordance with the target line number selected by the processing target line selection unit 501 and the displacement amount for each color component obtained by the displacement amount control unit 502. Read data. Then, the sub-scanning direction displacement processing unit 504 obtains displacement image data in the same manner as described in the first embodiment. The color composition processing unit 505 obtains composite color data in the same manner as in the first embodiment, based on the displacement image data obtained by the sub-scanning direction displacement processing unit 504. The correlation calculation processing unit 506 reads reference image data of a color component serving as a reference stored in the input image memory 503 in accordance with the target line number selected by the processing target line selection unit 501. The correlation degree calculation processing unit 506 calculates the degree of correlation with the synthesized color data by the color synthesis processing unit 505 in the same manner as in the first embodiment.

  The maximum correlation degree determination unit 507 calculates the maximum value of the correlation degree calculated by the correlation degree calculation processing unit 506 and the “displacement amount for each color component” (displacement determined by the displacement amount control unit 502) that maximizes the correlation degree. Quantity). When the attention line number selected by the processing target line selection unit 501 is different from the attention line number designated immediately before, the maximum correlation degree determination unit 507 has a maximum degree of correlation with respect to the sub-scanning direction displacement processing unit 508. “Displacement amount for each color component” is notified. After notifying the sub-scanning direction displacement processing unit 508 of the “displacement amount for each color component” that maximizes the degree of correlation, the maximum degree-of-correlation determination unit 507 The “displacement amount for each color component” that maximizes the degree is reset. On the other hand, when the attention line number selected by the processing target line selection unit 501 is the same as the attention line number designated immediately before, the maximum correlation degree determination unit 507 calculates the correlation newly obtained by the correlation degree calculation processing unit 506. The degree is compared with the maximum correlation degree so far. Then, the maximum correlation degree determination unit 507 determines that the correlation degree newly obtained by the correlation degree calculation processing unit 506 is larger than the maximum correlation degree held so far in the maximum correlation degree determination unit 507. The following processing is performed. That is, the maximum correlation degree determination unit 507 updates the maximum value of the correlation degree and the displacement amount corresponding to the maximum value of the correlation degree to the newly obtained one.

The sub-scanning direction displacement processing unit 508 receives the target line number selected by the processing target line selection unit 501 and the “displacement amount for each color component” notified from the maximum correlation degree determination unit 507 and having the maximum correlation degree. Based on the above, the image data stored in the input image memory 503 is read out. Further, the sub-scanning direction displacement processing unit 508 obtains displacement image data for the image data read from the input image memory 503 in the same manner as the sub-scanning direction displacement processing unit 504, and the displacement image data is obtained in the sub-scanning direction. The result is stored in the output image memory 509 as a result of the color misregistration correction process.
By configuring as described above, it is possible to perform color misregistration correction processing in the sub-scanning direction without performing multiple color synthesis processing and correlation degree calculation processing in parallel, thereby further reducing the cost of mounting. . In this embodiment, in order to clarify the explanation, the sub-scanning direction displacement processing unit 504 and the sub-scanning direction displacement processing unit 508 are intentionally divided and illustrated, but the processing contents are the same. Therefore, a common circuit may be used.

(Third embodiment)
Hereinafter, a third embodiment will be described. In the first and second embodiments described above, the degree of correlation between the reference image data and the composite color data is obtained. On the other hand, in the present embodiment, difference image data obtained by taking a difference in the sub-scanning direction is generated for each of the reference image data and the composite color data, and the degree of correlation between the difference image data is obtained. As described above, the present embodiment is different from the first and second embodiments described above mainly in part of the processing when performing color misregistration correction. Therefore, in the description of the present embodiment, the same parts as those in the first and second embodiments described above are denoted by the same reference numerals as those in FIGS.

FIG. 7 is a flowchart for explaining an example of the operation of the image processing apparatus when performing color misregistration correction processing in the sub-scanning direction. Here, for convenience of explanation, description will be made based on the block diagram shown in FIG. In the example shown in FIG. 7, as in the second embodiment, it is assumed that the image data stored in the input image memory is processed after reading.
First, in step S <b> 701, the processing target line selection unit performs initialization processing for each page of the document 201. Specifically, the processing target line selection unit resets a target line counter that determines which line of the reference image data is to be processed as a target line.
In the next steps S702 and S703, initialization processing is performed for each line in the sub-scanning direction (for each target line). Specifically, in step S <b> 702, the correlation degree calculation processing unit resets the maximum value of the correlation degree referred to in the subsequent color misregistration correction process and the “displacement amount for each color component” that maximizes the correlation degree. Next, in step S703, the displacement amount control unit resets a repetition number counter that holds the number of repetition processes for each target line.

Next, in step S704, the displacement amount control unit determines a displacement amount for each color component. Specifically, similarly to the second embodiment, the displacement amount control unit determines the color component based on the displacement amount reference value of each color component and the displacement amount difference corresponding to the number of repetitions shown in the table shown in FIG. The amount of displacement for each is determined.
Next, in step S705, the sub-scanning direction displacement processing unit obtains first displacement image data and second displacement image data. Specifically, as in the second embodiment, the sub-scanning direction displacement processing unit refers to the image data stored in the input image memory 503 based on the value of the target line counter and the displacement amount for each color component. The line is read and weighted average processing is performed as necessary to obtain displacement image data. More specifically, the sub-scanning direction displacement processing unit corresponds to the first displacement image data corresponding to the displacement amount obtained in step S704 and the displacement amount obtained by shifting the displacement amount obtained in step S704 by one line. Two types of displacement image data with the second displacement image data are calculated. Here, the displacement amount is set so that the second displacement image data precedes the first displacement image data by one line in the sub-scanning direction. The two types of displacement image data differ only in the amount of displacement, and their calculation methods are the same.

Next, in step S706, the color composition processing unit obtains first composite color data corresponding to the first displacement image data and second composite color data corresponding to the second displacement image data. Specifically, as in the first embodiment, the color composition processing unit performs a composite color corresponding to the color component of the reference image data according to the characteristics of the color image sensor 204 used to obtain the input image data. Data is obtained for each of the first and second displacement image data.
Next, in step S707, the color composition processing unit obtains first difference image data and second difference image data. Specifically, the color composition processing unit obtains, as first difference image data, image data of a difference between a target line in the reference image data in the input image data and a line adjacent to the target line. Here, the line adjacent to the target line is, for example, a line preceding the target line in the sub-scanning direction. In addition, the color composition processing unit obtains the difference image data between the first composite color data and the second composite color data as the second difference image data.
For example, when the first difference image data is generated by subtracting the image data of the target line from the image data of the line adjacent to the target line, the first composite color data is obtained from the second composite color data. Subtraction is performed to generate second difference image data. On the other hand, when the first difference image data is generated by subtracting the image data of the line adjacent to the target line from the image data of the target line, the second composite color data is subtracted from the first composite color data. Second difference image data is generated.

Next, in step S708, the correlation degree calculation processing unit calculates the degree of correlation between the first difference image data and the second difference image data by the same method as in the first embodiment.
Next, in step S709, the maximum correlation degree determination unit obtains the maximum correlation degree in the same target line. Specifically, the maximum correlation degree determination unit determines whether or not the correlation degree newly obtained in step S708 is equal to or less than the maximum correlation degree held so far. As a result of this determination, if the correlation degree newly obtained in step S708 is equal to or less than the maximum correlation degree held so far, the process proceeds to step S711, and if not, the process proceeds to step S710. In step S710, the maximum correlation degree determination unit updates the maximum value of the correlation degree and the “displacement amount for each color component” that maximizes the correlation degree. Then, the process proceeds to step S711.

In steps S711 to S713, it is determined whether or not to repeat the process for each target line. Specifically, in step S711, the displacement amount control unit updates the value of the repetition number counter indicating the number of repetition processes in the same target line (adds “1”).
Next, in step S712, the displacement amount control unit determines whether or not the maximum value of the degree of correlation exceeds a predetermined threshold value. As a result of this determination, if the maximum value of the degree of correlation exceeds a predetermined threshold value, the processing of the current attention line is aborted, and the process proceeds to step S714 to be described later. On the other hand, if the maximum value of the correlation does not exceed the predetermined threshold value, the process proceeds to step S713.
In step S713, the displacement amount control unit determines whether or not the value of the repeat count counter exceeds a predetermined repeat upper limit count. If the result of this determination is that the value of the repeat count counter exceeds the predetermined repeat upper limit count, the process for the current line of interest is aborted, and the process proceeds to step S714. Otherwise, the processes in and after step S704 are repeated.

Next, in step S714, the sub-scanning direction displacement processing unit performs displacement in the same manner as in step S704 based on the “displacement amount for each color component” obtained by the repetition processing for each line and having the maximum degree of correlation. Obtain image data. Here, the sub-scanning direction displacement processing unit obtains the first displacement image data, but obtains the second displacement image data instead of or in addition to the first displacement image data. Also good. In step S714, the displacement image data is stored in the output image memory as a result of the color misregistration correction process corresponding to the target line.
The next steps S715 and S716 relate to the determination for updating the line of interest and performing iterative processing. Specifically, in step S715, the processing target line selection unit updates the value of the target line counter (adds “1”). Next, in step S716, the processing target line selection unit determines whether or not the value of the target line counter has exceeded the final line number. If the result of this determination is that the value of the eye line counter does not exceed the final line number and the processing of the final line has not yet been completed, the processing from step S702 is repeated. On the other hand, when the value of the eye line counter exceeds the final line number and the processing of the final line is finished, the processing according to the flowchart of FIG. 7 is finished.
As described above, in the present embodiment, difference image data obtained by taking a difference in the sub-scanning direction is generated for each of the reference image data and the composite color data, the degree of correlation is obtained, and the “color” with the maximum degree of correlation is obtained. The displacement image data is selected based on the “displacement amount for each component”. Therefore, it is possible to perform color misregistration correction processing focusing on the edge component of the image data to be processed. Further, in this embodiment, since attention is paid to the edge component, the color shift generated in the contour portion is corrected regardless of the color of the character, and the color shift of the contour portion is corrected even if the background color is other than white. It is possible to more effectively perform the output of a clear image in which the above is corrected.
In this embodiment, the degree of correlation is calculated for each line and the output image data is obtained for each line. However, the degree of correlation is determined for each processing unit with a plurality of lines (line group) as one processing unit. The maximum “displacement amount for each color component” may be obtained.

In addition, each process of embodiment mentioned above can also perform the software (computer program) acquired via the network or various storage media with processing apparatuses (CPU, processor), such as a personal computer. Moreover, you may comprise the computer program itself which performs each process of this embodiment, and the storage medium in which the computer program was memorize | stored.
In addition, the above-described embodiments are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

Claims (8)

An acquisition means for acquiring image data for each line detected by a line sensor configured by arranging a plurality of line-shaped sensors for each color component in the sub-scanning direction;
A displacement image for each color component that is displaced in the sub-scanning direction by a displacement amount set for each color component with respect to image data having a color component different from a reference color component among the image data of the line. Displacement means for obtaining data;
Synthesizing displacement image data for each color component acquired by the displacement unit, and generating synthesized color data corresponding to the reference color component;
Deriving means for deriving a correlation between the combined color data generated by the combining means and the image data of the reference color component;
An image processing apparatus comprising: selection means for selecting displacement image data corresponding to composite color data having the highest correlation with the image data of the reference color component.   Of the color components different from the reference color component, the line sensor is closer to the reference color component sensor as the color component sensor having a higher correlation with the reference color component. The image processing apparatus according to claim 1, wherein the image processing apparatus is arranged.   Among the color components different from the reference color component, the line sensor is arranged closer to the reference color component sensor as the lightness of the color component is higher. The image processing apparatus according to claim 1.   As the displacement amount, a displacement amount obtained by adding a positive value to a reference displacement amount is set for image data in a predetermined range, and a reference amount is set for image data in another predetermined range. The image processing apparatus according to claim 1, further comprising: a displacement amount control unit that sets a displacement amount obtained by adding a negative value to the displacement amount to be obtained. Displacement amount control means for resetting the displacement amount each time correlation is derived by the derivation means until a predetermined condition is satisfied,
The selecting means selects the displacement image data corresponding to the composite color data having the highest correlation with the image data of the reference color component among the correlations derived by the deriving means until the predetermined condition is satisfied. The image processing apparatus according to claim 1, wherein the image processing apparatus is selected. A generation unit that generates difference image data that is a difference between the image data of the line or line group to be processed and the image data of the line or line group adjacent to the line or line group in the sub-scanning direction;
The displacement means performs sub-scanning for image data of a color component different from a reference color component among image data of the line or line group to be processed by a displacement amount set for each color component. Generating first displacement image data displaced in the direction, and generating second displacement image data in which a displacement amount differs from the first displacement image data by one line or a predetermined plurality of lines,
The generating means includes the image data of the reference color component in the line or line group to be processed, and the line or line group adjacent to the line or line group to be processed in the sub-scanning direction, First difference image data which is a difference from image data of a reference color component, first synthesized color data generated by the synthesizing unit based on the first displacement image data, and the second Generating second difference image data that is a difference from the second synthesized color data generated by the synthesizing unit based on the displacement image data;
The derivation means derives a correlation between the first difference image data and the second difference image data,
The selection means is a displacement image corresponding to the second difference image data having the highest correlation among the correlation between the plurality of second difference image data having different displacement amounts and the first difference image data. 6. The image processing apparatus according to claim 1, wherein data is selected. An acquisition step of acquiring image data for each line detected by a line sensor configured by arranging a plurality of line-shaped sensors for each color component in the sub-scanning direction;
A displacement image for each color component that is displaced in the sub-scanning direction by a displacement amount set for each color component with respect to image data having a color component different from a reference color component among the image data of the line. A displacement step for acquiring data;
Synthesizing displacement image data for each color component acquired by the displacement step, and generating a synthesized color data corresponding to the reference color component;
A derivation step for deriving a correlation between the combined color data generated by the combining step and the image data of the reference color component;
And a selection step of selecting displacement image data corresponding to the composite color data having the highest correlation with the image data of the reference color component. An acquisition step of acquiring image data for each line detected by a line sensor configured by arranging a plurality of line-shaped sensors for each color component in the sub-scanning direction;
A displacement image for each color component that is displaced in the sub-scanning direction by a displacement amount set for each color component with respect to image data having a color component different from a reference color component among the image data of the line. A displacement step for acquiring data;
Synthesizing displacement image data for each color component acquired by the displacement step, and generating a synthesized color data corresponding to the reference color component;
A derivation step for deriving a correlation between the combined color data generated by the combining step and the image data of the reference color component;
A computer program causing a computer to execute a selection step of selecting displacement image data corresponding to composite color data having the highest correlation with image data of a reference color component.

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