JP6808974B2 - Image processing equipment and computer programs - Google Patents

Description

The present invention relates to an image processing device and a computer program.

A color copier, a color scanner, and a color facsimile machine include an image sensor that reads a color image from a document sheet and an image processing unit that processes the read color image data (color data).

Generally, a reduced color CCD sensor is used as an image sensor. In the reduced color CCD sensor, the element sequences of R (red), G (green), and B (blue) in which the pixels are arranged in the main scanning direction are parallel to each other with a predetermined interval d in the sub scanning direction. It has an arranged structure. That is, the reading positions of the R, G, and B colors in the sub-scanning direction deviate from each other.

The image processing unit performs inter-line correction on the color data obtained by such a reduced color CCD sensor. The line-to-line correction is a process for correcting the deviation of the reading position of each of the R, G, and B colors in the sub-scanning direction.

When the deviation of the reading position is not an integral multiple of the above interval d, the image processing unit performs integer part correction and decimal part correction as interline correction. The integer part correction is a process of delaying the color data to be read ahead with respect to other colors by the same number of lines as the integer part of the deviation amount. The decimal part correction is a process of correcting a deviation of less than one line by performing interpolation calculation according to the decimal part of the deviation amount for the data of each color.

By the way, it is known that there is a problem that black thin lines and edges of black characters are colored (a phenomenon in which achromatic color becomes chromatic) by performing decimal part correction. Then, as a prior art for reducing the coloring due to the correction of the decimal part, there are the techniques described in Patent Documents 1 and 2.

Patent Document 1 discloses that the reading reference position is set so that the decimal part of the reading position deviation is equivalent among the three colors R, G, and B. Patent Document 2 discloses that a smoothing process is performed before the decimal part correction is performed.

JP-A-2002-247292 Japanese Unexamined Patent Publication No. 2014-236294

According to the technique of Patent Document 1 described above, interpolation processing is performed for any of the three colors R, G, and B as a decimal part correction. Since the interpolation process is also performed on G having a high luminosity function, there is a problem that a decrease in resolving power (image blurring) due to interpolation becomes conspicuous. As the decimal correction amount approaches 0.5, the blurring of the image becomes more remarkable.

According to the technique of Patent Document 2, there is a problem that the resolving power is lowered by adding the smoothing process. There is also a problem that the circuit scale of the image processing unit increases. When the sharpness processing is performed after the decimal part correction in order to compensate for the decrease in the resolving power due to the smoothing processing, the circuit scale is further increased.

The present invention has been made in view of the above problems, and an object of the present invention is to realize image processing with less coloring and blurring.

In the image processing apparatus according to the embodiment of the present invention, each color of the color image is read by an image sensor in which element trains of each color in the main scanning direction are arranged in parallel with each other at intervals in the sub scanning direction. An image processing device that processes color data whose reading positions in the sub-scanning direction are different from each other, and is corrected by an inter-line correction unit that corrects the deviation of the reading position in the sub-scanning direction of the color data and the interline correction unit. The color data in which the above is performed is provided with a color shift correction unit for correcting the color shift component in the sub-scan direction caused by factors other than the shift in the reading position in the sub-scan direction for each pixel, and between the lines. The correction unit has at least a fractional part correction unit that corrects a deviation of less than one line by interpolation processing, and the minority part correction unit performs the sub-scanning on color data of a non-reference color in the color data. performs interpolation processing using the correction amount larger than 0 rather smaller than calculating the correction amount is a correction amount of less than one line, which is calculated based on the deviation in the direction of the reading position, in the color misregistration correction unit, the color The correction is performed using the color shift correction amount obtained by adding the remaining correction amount that was not corrected by the fractional part correction unit of the calculated correction amount to the correction amount corresponding to the deviation component .

According to the present invention, it is possible to realize image processing with less coloring and blurring.

It is a figure which shows the outline of the structure of the image processing apparatus which concerns on one Embodiment of this invention. It is a figure which shows an example of the structure of an image sensor. It is a figure which shows another example of the structure of an image sensor. It is a figure which shows the structure of the image processing part which is the main part of an image processing apparatus. It is a figure which shows the example of the parameter used for the line-to-line correction and the color shift correction. It is a figure which shows other example of the parameter used for line-to-line correction and color shift correction. It is a figure which shows the example of the color data which read the black thin line. It is a figure which shows the example of the line-to-line correction and the color shift correction. It is a figure which shows the comparative example of the line-to-line correction and the color shift correction.

FIG. 1 shows an outline of the configuration of the image processing device 1 according to the embodiment of the present invention, FIG. 2 shows an example of the configuration of the image sensor 51, and FIG. 3 shows another example of the configuration of the image sensor 52. Each is shown.

The image processing device 1 is, for example, an MFP (Multi-functional Peripheral: a multifunction device or a multifunction device), and has a function of processing color data. The image processing device 1 includes a CPU 11, a ROM 12, a RAM 13, an image memory 14, an image reading unit 21, an image processing unit 22, a printer unit 23, an operation panel 24, and the like.

The CPU 11 is in charge of controlling the entire image processing device 1. The CPU 11 loads the program stored in the ROM 12 into the RAM 13 and executes the program. At that time, control data is loaded as needed. When a job is input by the user using the operation panel 24, the CPU 11 controls the operation of each part of the image processing device 1 so as to execute the job.

The image reading unit 21 optically reads the color image recorded on the document sheet by using the image sensor 51 shown in FIG. 2 or the image sensor 52 shown in FIG. The image reading unit 21 includes, for example, an automatic document feeder and a flat-head type scanner. The automatic document feeder reads the image while transporting the document sheet. The scanner reads an image from a document sheet placed on a platen glass. The image reading unit 21 sends the read color image data (color data D21) to the image processing unit 22.

It is assumed that the color data D21 is data of 256 gradations in which the brightness of each color of R, G, and B is represented by 8 bits for each pixel. The data value is large for light pixels and small for dark pixels. In the white pixel, the data values of all three colors are the maximum value "255", and in the black pixel, the data values of all three colors are the minimum value "0".

The image processing unit 22 performs image processing including interline correction processing and color shift correction processing described later on the color data D21 input from the image reading unit 21, and outputs the processed color data D22. For example, in a copy job, the color data D22 processed by the image processing unit 22 is temporarily stored in the image memory 14 and then sent to the printer unit 23.

The printer unit 23 prints a color image corresponding to the sent color data D22 on paper. At that time, the light emission of the print head 231 is controlled based on the color data D22. The printing method is an electrophotographic method. However, an inkjet method or another method may be used.

The image sensor 51 shown in FIG. 2 is a reduced color CCD sensor that reads a document image reduced and projected by an optical system. The image sensor 51 has element rows 51R, 51G, 51B of each color of R, G, and B in which pixels (light receiving elements) are arranged in the main scanning direction M1. The element rows 51R, 51G, and 51B are arranged in parallel with each other in the sub-scanning direction M2 with an interval d. The interval d is an integral multiple (for example, 4 times) of the line pitch in reading at the same magnification.

In the reading by the image sensor 51, a fluorescent lamp or a white LED is used as the light source, and the main scan and the sub scan are performed with the light source turned on continuously. Since the element trains 51R, 51G, and 51B are arranged in the order of R, G, and B from the downstream side of the sub-scanning direction M2, R is pre-read with respect to G and B is pre-read with respect to G.

The deviation of the reading position between each of R and B and G varies depending on the scan magnification. When the scan magnification is "1", that is, when reading at the same magnification, the deviation of the reading position is 4 lines, and only the integer part correction needs to be performed as the interline correction.

However, in reading other than the same magnification, the deviation of the reading position becomes a decimal, so it is necessary to correct the integer part and the decimal part. For example, when an A4 size original image is enlarged to A3 size and printed, the scan magnification is "1.414" and the deviation of the reading position is 5.656 lines. Therefore, in this case, the integer part correction of 5 lines and the decimal part correction of 0.656 lines are performed.

The image sensor 52 shown in FIG. 3 is a contact image sensor (CIS) that reads an image by one element array in which pixels (light receiving elements) are arranged in the main scanning direction M1. In the image sensor 52, an element train, a light source, a 1x imaging system lens, a drive control circuit, and the like are integrated.

In the reading by the image sensor 52, LEDs of each color of R, G, and B are used as a light source, and the color image is read by turning on these LEDs in sequence. Each LED emits light when the corresponding signal among the lighting signals LED_R, LED_G, and LED_B is at a low level.

The reading period for one line, which is the pulse period of the synchronization signal TG, is read in the order of R, G, and B by time division dividing into three equal parts. The read color data D21 of R, G, and B is output in accordance with the synchronization signal TG.

Hereinafter, the function of the image processing unit 22 will be described assuming that the image sensor 52 is used. In the following, the image sensor 52 may be referred to as a “close contact type image sensor 52”.

FIG. 4 shows the configuration of the image processing unit 22 which is a main part of the image processing device 1, and FIG. 5 shows an example of parameters f1, f2, and f3 used for line-to-line correction and color shift correction, respectively. Has been done.

The image processing unit 22 processes the color data D21 having different reading positions in the sub-scanning direction M2 for each color of the color image read from the original sheet. In addition, this processing has a first processing mode and a second processing mode.

The image processing unit 22 includes a shading correction unit 31, an interline correction unit 32, a color shift correction unit 35, an image correction unit 36, a line width detection unit 38, a density detection unit 39, an area discrimination unit 40, and the like. .. The functionality of these elements is achieved by hardware, software, or a combination of both.

The shading correction unit 31 is caused by the characteristics of the illumination system, the imaging system, and the photographing system in the image reading unit 21 with respect to the color data D21 of each color of R, G, and B input in parallel from the image reading unit 21. Shading correction processing for removing the distortion in the main scanning direction M1 is performed.

The inter-line correction unit 32 performs inter-line correction processing on the color data D31 input from the shading correction unit 31 to correct the deviation of the reading position of the non-reference color in the sub-scanning direction M2 with respect to the reference color. The reference color is a reference color for determining the deviation of the reading position among R, G, and B. The reading position of the non-standard color deviates from the reading position of the standard color, but the standard color does not deviate from the reading position. Therefore, it is not necessary to correct between lines for the reference color.

In the present embodiment, the reference color is G, which has the highest relative luminosity among R, G, and B. By setting the reference color to G, in other words, by using R and B, which are less noticeable than G even if the image is blurred due to the line-to-line correction, as non-standard colors, the deterioration of the image quality due to the line-to-line correction is suppressed. be able to.

The inter-line correction unit 32 includes an integer part correction unit 33 that corrects an integer part and a decimal part correction unit 34 that corrects a decimal part.

The integer part correction is a correction in units of one line in which the color data D31 of the pre-read color is delayed by using the line memory. When the integer part correction is not required, the integer part correction unit 33 sends the color data D31 input from the shading correction unit 31 to the decimal part correction unit 34 as the color data D33 without performing substantial processing. ..

The decimal part correction is a correction of a deviation of less than one line in which all pixels are uniformly interpolated for each of the non-reference color (R, B) color data D33 input from the integer part correction unit 33.

The decimal part correction unit 34 has a correction amount f22 smaller than the calculated correction amount f21, which is a correction amount of less than one line calculated based on the deviation of the reading position in the sub-scanning direction M2 with respect to the color data D33 of the non-reference color. Is used to perform interpolation processing (bilinear interpolation processing) based on the data values of two pixels arranged in the sub-scanning direction M2 of adjacent lines. The positions (main scanning positions) of the two pixels in the main scanning direction M1 are the same.

As described above, when the close contact type image sensor 52 is used, R is pre-read by 1/3 line with respect to G, and the reading position of R is shifted by 1/3 line to the downstream side. Further, B is read after 1/3 line with respect to G, and the reading position of B is shifted 1/3 line to the upstream side. These deviations inevitably occur in time division reading. Since the calculated correction amount f21 in this case is "1/3", the correction amount f22 is larger than 0 and smaller than 1/3 (≈0.33). For example, the correction amount f22 is set to "1/6" (≈0.17), which is half of 1/3. It may be another value.

The decimal part correction unit 34 performs the interpolation operation represented by the equation (1) for delaying the color data D33 of the read-ahead R, and is represented by the equation (2) for accelerating the color data D33 of the read-ahead B. Interpolation operation is performed. Then, the obtained R data Rout and B data Bout are output to the subsequent stage as the color data D34 of the line of interest.

Rout = R (n) x (1-f22) + R (n + 1) x f22 ... (1)
However,
R (n): Color data D33 of the line of interest
R (n + 1): Color data D33 one line downstream of the line of interest
f22: Correction amount smaller than the calculated correction amount f21 Bout = B (n) × (1-f22) + B (n-1) × f22… (2)
However,
B (n): Color data D33 of the line of interest
B (n-1): Color data D33 one line upstream of the line of interest
When the color data D33 does not correspond to a black thin line having a width of 1 dot extending in the main scanning direction M1, the decimal part correction unit 34 uses the calculated correction amount f21 instead of the correction amount f22 smaller than the calculated correction amount f21. Interpolation processing may be performed.

Further, when the density of the color data of the reference color in the color data D33 is not higher than the density of the color data of the non-reference color plus the margin value, the fractional part correction unit 34 is calculated from the calculation correction amount f21. The interpolation processing may be performed using the calculated correction amount f21 instead of the small correction amount f22.

The color shift correction unit 35 performs color shift correction processing for correcting the color shift component in the sub-scanning direction M2 for each pixel on the color data D34 of the non-reference color corrected by the line-to-line correction unit 32. Substantial processing is not performed on the color data D34 of the reference color. The color data D34 of the reference color is sent to the subsequent stage as it is.

The color shift component in the sub-scanning direction M2 is a density shift caused by an inevitable shift in the reading position in the sub-scanning direction M2 or other factors. Other factors, indefinite displacement due to vibration of the image sensor 52 during reading, R, G, there etc. Lena not focus position by MTF difference between B.

The color shift correction unit 35 makes corrections according to the remaining correction amount that was not corrected by the decimal part correction unit 34 of the calculated correction amount f21. Specifically, the color shift correction amount f30 obtained by adding the remaining correction amount f32 of the decimal part correction to the correction amount f31 corresponding to the color shift component in the sub-scanning direction M2 is used for correction by interpolation processing based on the data of a plurality of lines. I do.

The color shift correction unit 35 has the lowest saturation of each of the non-reference color color data D34, including the reference color color data D34, among the color data D34 of the plurality of pixels before and after each. Color data D34 is selected and corrected. That is, the color of the pixel of interest is corrected so as to be closer to the achromatic color.

Specifically, each of the color data D34 of R and B is subjected to an interpolation calculation using a plurality of correction amounts f30 predetermined as options for the color shift correction amount f30, and among the obtained calculation results. Therefore, the calculation result having the smallest difference from the color data D34 of G is output as the color data D35 after the color shift correction. This corresponds to selecting the correction amount having the smallest difference from G from a plurality of options and using it for color shift correction.

When the color data D33 does not correspond to the black thin line extending in the main scanning direction M1, the color shift correction unit 35 corrects using the correction amount f31 corresponding to the color shift component instead of the color shift correction amount f30. It may be a thing.

Further, the color shift correction unit 35 determines the color shift correction amount f30 when the density of the color data of the reference color in the color data D33 is not higher than the density of the color data of the non-reference color plus a margin value. Instead of, the correction may be performed using the correction amount f31 corresponding to the color shift component.

The line width detection unit 38 detects the line width in the sub-scanning direction M2 by using a known image discrimination technique based on the color data D31 after the shading correction process. This detection detects thin lines in which color shift is likely to occur when interline correction is performed using the calculated correction amount f21. By detecting the line width, the decimal part correction using the correction amount f22 smaller than the calculated correction amount f21 can be performed only for the thin line, and the deviation of the reading position can be corrected by using the calculated correction amount f21 for the other parts. It will be possible.

Specifically, the line width detection unit 38 extracts a line having a width of 1 dot, and notifies the decimal part correction unit 34 of the pixel position of the extracted line as detection data D38.

The density detection unit 39 detects the density of each of the colors R, G, and B based on the color data D31 after the shading correction process. In this detection, the decimal part correction is performed only when the density relationship between the standard color and the non-standard color is effective for the decimal part correction, and the non-standard color is detected when the decimal part correction is performed regardless of the density relationship. This is to prevent the image from being blurred and as a result, the color shift from G is increased.

Based on the detected density, the density detection unit 39 determines whether G is darker than each of R and B in the state before the line-to-line correction, and uses the determination result as the detection data D39 to correct the decimal part 34. Notify to. The determination is made based on, for example, the following equation (3). When the formula (3) holds, it is determined that G is darker than each of R and B.

Min (R, B)> DG + Ref ... (3)
However,
Min (R, B): The minimum value (that is, the maximum density) of the respective densities of R and B in a predetermined number of adjacent pixels in the sub-scanning direction M2.
DG: G density of the pixel in which the respective densities of R and B are the minimum Ref: A margin value set to improve the reliability of the determination Such a density detection unit 39 and the line width detection unit 38 described above. As a result, the black thin line detection unit 37 that detects whether or not the color data D31 corresponds to the black thin line extending in the main scanning direction M1 is configured.

Based on the color data D35 after the color shift correction processing, the area discrimination unit 40 discriminates the edge portion in the original image, determines the color for each region of a predetermined unit, and corrects the region discrimination data D40 showing the results. Notify department 36.

In order to improve the accuracy of color determination in the area determination unit 40, it is necessary for the color shift correction unit 35 to sufficiently correct the color shift component in the sub-scanning direction M2.

The image correction unit 36 performs correction processing for improving the image quality of the color data D35 after the color shift correction processing, based on the area discrimination data D40 from the area discrimination unit 40. For example, sharpness processing is applied to the edge part to make it clear, and for pixels judged to be black by color judgment, the density of R and B is made the same as the density of G to make monochrome (achromatic). Or something.

In FIG. 5, a comparative example is shown together with an example of the parameters f1, f2, and f3. Examples of the parameters f1, f2, and f3 are collectively stored in the table T1 in advance in the non-volatile memory in the image processing apparatus 1, and are used by the image processing unit 22 in the first processing mode.

The integer part correction parameter f1 corresponds to the integer part of the deviation amount of the reading positions of R, G, and B, and represents the number of lines to be delayed in the integer part correction unit 33. When the close contact type image sensor 52 is used, the parameter f1 is "0".

The decimal part correction parameter f2 is used for interpolation processing in the decimal part correction unit 34. Since the interpolation process is not performed on the reference color G, the parameter f2 of G is “0”.

In the embodiment, the parameter f2 for the decimal part correction is a calculated correction amount corresponding to the decimal part (1/3) of the deviation amount (± 1/3 ≈ ± 0.33) of the reading position between R, G, and B. The correction amount f22 has an absolute value smaller than that of f21. In the embodiment, 1/6 of half of the calculated correction amount f21 is set as the parameter f2 of the non-reference colors R and B. On the other hand, in the comparative example, the parameter f2 of R and B is the calculated correction amount f21.

The symbol "-" in the parameter f2 for the decimal part correction indicates that the calculation is performed using the above-mentioned equation (1), and the symbol "+" indicates that the calculation is performed using the equation (2). ..

The color shift correction parameter f3 is used for the interpolation process in the color shift correction unit 35. Since the interpolation process is not performed on the reference color G, the parameter f3 of G is “0”.

In the embodiment, the color shift correction parameter f3 is the remaining correction not corrected by the decimal part correction unit 34 of the calculated correction amount f21 to the correction amount f31 corresponding to the color shift component caused by the vibration or the MTF difference. The color shift correction amount f30 is obtained by adding the amount f32. However, considering that there are pixels that do not need correction such as non-edge parts and pixels that should not be corrected as a result, the numerical value (“0”) indicating that the original data value is output as it is is also parameter f3. Included in.

A plurality of options are predetermined for the color shift correction amount f30. For example, for R, (-1 / 8-1 / 6) = -7/24, (0-1 / 6) = -1/6, (1 / 8-1 / 6 = -1/24) 3 There are two options.

Negative values (-1/8) and positive values (+1/8) are defined as the correction amount f31 in these options on the downstream side for vibration, which is one of the causes of color shift components. This is because there is a runout to the upstream side and a runout to the upstream side.

Further, the absolute value (1/6) of -1/6, which is the remaining correction amount f32, is represented by the following equation (4) which is commonly applied to R and B. Since R is interpolated so as to shift (delay) to the downstream, it is set to a negative value.

| Remaining correction amount f32 | = (Calculated correction amount f21)-(Parameter f22 ) ... (4)
When the parameter f3 has a negative value, the color shift correction unit 35 performs the interpolation operation represented by the equation (5), and when the parameter f3 has a positive value, the color shift correction unit 35 performs the interpolation operation represented by the equation (6). ..

Dout = D (n) x (1-f3) + D (n + 1) x f3 ... (5)
Dout = D (n) x (1-f3) + D (n-1) x f3 ... (6)
However,
D (n): Color data D34 of the pixel of interest
D (n + 1): Color data D 34 of a pixel at the same main scanning position one line downstream of the pixel of interest.
D (n-1): Color data D 34 of a pixel at the same main scanning position one line upstream of the pixel of interest.
FIG. 6 shows other examples of parameters f1, f2, and f3 used for line-to-line correction and color shift correction. The parameters f1, f2, and f3 of FIG. 6 are collectively stored in the table T2 in advance in the image processing apparatus 1, and are used by the image processing unit 22 in the second processing mode. The second processing mode is different from the first processing mode in that the processing content is changed according to the detection data D38 and D39 by the line width detection unit 38 and the density detection unit 39.

Parameters f1 used when "the color data D31 of the pixel of interest corresponds to a line having a width of 1 dot and the density of G is higher than the density of each color data D31 of R and B plus a margin value". f2 and f3 are the same as the parameters f1, f2 and f3 in the embodiment (table T1) of FIG.

The parameters f1, f2, f3 used in the other cases are the same as the parameters f1, f2, f3 in the comparative example of FIG. In other cases, the color data D31 does not correspond to the thin black line L1 extending in the main scanning direction, and the color data D31 of the reference color (G) has a density of the non-reference color (R, B). This includes cases where the concentration is not higher than the concentration obtained by adding a margin value to the concentration of.

FIG. 7 shows an example of color data D31 in which the thin black line L1 is read. The left-right direction in the figure corresponds to the reading sub-scanning direction M2, and the front-back direction of the paper surface corresponds to the main scanning direction M1. The thin black line L1 is a black line having a width of 1 dot extending in the main scanning direction M1.

In FIG. 7A, the reading position of G is exactly the center of the sub-scanning direction M2 of the black thin line L1, and the G component of the black thin line L1 is read most densely. In this case, if R is interpolated based on R (n) and R (n + 1), and B is interpolated based on B (n) and R (n-1), a decimal part correction process is performed. , R, and B are all treated so as to be light, so that the density difference (color shift component) from G (n) increases. Therefore, there is a high possibility that black is erroneously determined as a chromatic color in the color determination by the area determination unit 40.

That is, when G is darker than other colors when a thin line is read, a correction amount f22 smaller than the calculated correction amount f21 is used, and the reading position shifts according to the above equations (1) and (2). Should be corrected weaker (less) than it should be.

On the other hand, in FIG. 7B, the reading position of R is exactly the center of the sub-scanning direction M2 of the black thin line L1, and the R component of the color of the black thin line L1 is read most intensely. In this case, when the decimal part correction processing is performed on R and B, both R and B are processed so as to be light. However, since R approaches G (n), the difference in concentration between R and B and G (n) is smaller than in the case of FIG. 7 (A). This means that there is a high possibility that black is correctly determined in the color determination by the area determination unit 40.

That is, if G is not darker than other colors when the thin line is read, even if the decimal part correction process using the calculated correction amount f21 instead of the correction amount f22 smaller than the calculated correction amount f21 is performed. There is almost no problem in color determination by the area determination unit 40.

From these facts, in the image processing apparatus 1, two tables T1 and T2 are stored as described above so that the first processing mode and the second processing mode can be properly used.

FIG. 8 shows an example of line-to-line correction and color shift correction, and FIG. 9 shows a comparative example of line-to-line correction and color shift correction. In FIGS. 8 and 9, the color data D31 obtained by reading the black line L3 having a width of 3 dots and the thin black line L1 having a width of 1 dot is subjected to line-to-line correction processing and color shift correction processing.

In the reading by the close contact type image sensor 52, each color of R, G, and B is read with a deviation of about 1/3 line. Therefore, in the color data D31 before the line-to-line correction, the end portion of the black line L3a and the thin black line L1a are colored. In this state, as shown by being surrounded by an ellipse C1 in the figure, there is a density difference (color shift component) dD1 between G, R, and B of the thin black line L1a.

The color data D34 after the inter-line correction is data obtained by subjecting the color data D31 to interpolation processing represented by the equations (1) and (2) as a decimal part correction processing. That is, by using the correction amount f22 smaller than the calculated correction amount f21, the deviation of the 1/3 line is intentionally weakly corrected.

Due to the weak correction, the black line L3b and the black thin line L1b remain colored in the color data D34. However, it should be noted that the density difference dD2 between G, R, and B of the 1-dot wide black thin line L1b is hardly increased (enlarged) as compared with the density difference dD1 before correction.

The color data D35 after the color shift correction is data obtained by performing the interpolation processing of the formula ( 5 ) or the formula ( 6 ) as the color shift correction processing on the color data D34.

In the black line L3c of the color data D35, the color shift is corrected so that the densities of R and B at the edges approach the dark densities at the center, so that the coloring is improved. That is, it is blackish as a whole.

Further, in the black thin line L1c having a width of 1 dot, the density difference dD2 between G, R, and B is the same as that before the color shift correction. This is because there are no dark pixels on both sides of the thin black line L1 (before and after in the sub-scanning direction M2), so that the parameters f3 that keep the R and B densities unchanged are selected and corrected in the color shift correction processing. is there.

As described above, for the black thin line L1c having a width of 1 dot, it is effective that the density of the non-reference color does not change in the color shift correction process, and the effect of weakly correcting the density difference dD1 in the decimal part correction process is suppressed. Since it is maintained, the coloring of the entire image is reduced.

On the other hand, in the comparative example of FIG. 9, the color data D34 after the inter-line correction calculates the correction amount f22 of the equations (1) and (2) as the decimal part correction process for the color data D31. It is the data subjected to the interpolation processing represented by the formula replaced with. That is, by using the calculated correction amount f21 larger than the correction amount f22, the deviation of the 1/3 line is corrected so as to be completely corrected.

By performing interpolation processing so as to completely correct the deviation of 1/3 line as the correction between lines, the density difference dD3 between G, R, and B of the black thin line L1b having a width of 1 dot is corrected in the color data D34. It is increased compared to the previous concentration difference dD1. Far from improving the coloring, the deterioration is remarkable.

Since there are no dark pixels in the front and back of the thin line as described above, the increased density difference dD3 remains as it is even if the color shift correction processing is subsequently performed. That is, the inter-line correction and the color shift correction improve the reproducibility of black for the black line L3b thicker than 1 dot width, but reduce the reproducibility for the black thin line L1b with 1 dot width.

According to the above embodiment, the calculation correction amount f21 for the decimal part correction is proportionally divided into an interpolation process that is uniformly performed for all pixels in the decimal part correction unit 34 and an interpolation process that is performed for each pixel in the color shift correction unit 35. Therefore, the coloring generated by the thin black line L1 can be reduced. Further, since G having a high luminosity function is used as a reference color and no line-to-line correction and color shift correction are performed on G, blurring of an image can be reduced.

Further, by performing the decimal correction weakly only for the pixels that meet the setting conditions of the line width and the density, it is possible to reduce the color shift (increase in the density difference) that occurs in the black thin line L1 by the interpolation processing.

In the embodiment described above, in the second processing mode, the decimal part is weak when the width is 1 dot and G is darker than R and B, that is, when both the line width and the density setting conditions are met. Although it has been described as performing correction, it is not limited to this. When only the line width setting condition is applied, or when only the density setting condition is applied, the decimal part correction may be weakly performed.

Even when reading is performed using the reduced image sensor 51 shown in FIG. 2, the calculated correction amount f21 can be proportionally divided into the decimal part correction and the color shift correction, thereby reducing the coloring. In that case, the pattern meters f1, f2, and f3 may be set according to the calculated correction amount f21 determined by the interval d of the element trains 51R, 51G, and 51B and the scan magnification.

The image processing device 1 may have at least the functions of the decimal part correction unit 34 and the color shift correction unit 35 of the image processing units 22, and may not have the image reading unit 21 and the printer unit 23. Good.

Although the reference color is G, B or R may be used as the reference color. For example, when processing data of a color image mainly composed of bluish colors, B is used as a reference color. This makes it possible to improve the reproducibility of blue.

In addition, the configuration of the entire image forming apparatus 1 or each part, the values of the parameter meters f1, f2, f3, the mathematical expression of interpolation, the number, type, order, timing, etc. of image processing performed by the image processing unit 22 are the objects of the present invention. It can be changed as appropriate according to.

1 Image processing device 32 Inter-line correction unit 34 Decimal part correction unit 35 Color shift correction unit 37 Black fine line detection unit 39 Density detection unit D21, D34 Color data dD1 Density difference (color shift component)
f21 Calculated correction amount f22 Correction amount smaller than the calculated correction amount f30 Color shift correction amount f31 Correction amount corresponding to the color shift component f32 Remaining correction amount G Reference color R, B Non-reference color M1 Main scanning direction M2 Sub-scanning direction

Claims (6)

Color data in which the reading positions in the sub-scanning direction are different from each other for each color of the color image by reading a color image by an image sensor in which element sequences of each color in the main scanning direction are arranged in parallel with each other at intervals in the sub-scanning direction. It is an image processing device that processes
An interline correction unit that corrects the deviation of the reading position in the sub-scanning direction of the color data, and
With respect to the color data corrected by the interline correction unit, a color shift correction unit for correcting the color shift component in the sub-scanning direction caused by factors other than the deviation of the reading position in the sub-scanning direction for each pixel. With,
The line-to-line correction unit
It has at least a decimal part correction unit that corrects deviations of less than one line by interpolation processing.
The decimal part correction unit is a correction amount of less than one line calculated based on the deviation of the reading position in the sub-scanning direction with respect to the color data of the non-reference color in the color data. Interpolation processing is performed using a correction amount that is smaller than 0 and is larger than 0.
In the color shift correction unit, correction is performed using a color shift correction amount obtained by adding the correction amount corresponding to the color shift component to the remaining correction amount of the calculated correction amount that was not corrected by the decimal part correction unit. Do, do
An image processing device characterized by this. The color shift correction unit obtains the color data of the non-reference color by performing an interpolation calculation on each of the plurality of color data before and after each of the color data by using a plurality of predetermined correction amounts. Correction is performed by selecting the color data that has the smallest difference from the standard color data among the color data.
The image processing apparatus according to claim 1. The color shift correction unit has the smallest difference between the color data of the non-reference color and the color data of the reference color from among a plurality of correction amounts predetermined as options for the color shift correction amount. Select the correction amount and use it for correction,
The image processing apparatus according to claim 1. A black thin line detection unit for detecting whether or not the color data corresponds to a black thin line having a width of 1 dot extending in the main scanning direction is provided.
When the color data corresponds to the black thin line, the decimal part correction unit performs interpolation processing using a correction amount smaller than the calculated correction amount and larger than 0, and the color data is the black. If it does not correspond to a thin line, interpolation processing is performed using the calculated correction amount.
When the color data corresponds to the black thin line, the color shift correction unit corrects using a color shift correction amount obtained by adding the remaining correction amount to the correction amount corresponding to the color shift component. When the color data does not correspond to the thin black line, the correction is performed using the correction amount corresponding to the color shift component.
The image processing apparatus according to any one of claims 1 to 3. A density detection unit for detecting the density of the color data of each color is provided.
When the density of the color data of the reference color in the color data is higher than the density of the color data of the non-reference color plus a margin value, the fractional part correction unit is smaller than the calculated correction amount and is 0. When the interpolation process is performed using a correction amount larger than the correction amount and the density of the color data of the reference color in the color data is not higher than the density of the color data of the non-reference color plus a margin value, the above Interpolate processing using the calculated correction amount
The color shift correction unit corrects the color shift component when the density of the color data of the reference color in the color data is higher than the density of the color data of the non-reference color plus a margin value. Correction is performed using the color shift correction amount obtained by adding the remaining correction amount to the amount, and the density of the color data of the reference color in the color data is the density of the color data of the non-standard color plus a margin value. If it is not higher than, the correction is performed using the correction amount corresponding to the color shift component.
The image processing apparatus according to any one of claims 1 to 3. Color data in which the reading positions in the sub-scanning direction are different from each other for each color of the color image by reading a color image by an image sensor in which element sequences of each color in the main scanning direction are arranged in parallel with each other at intervals in the sub-scanning direction. A computer program used in an image processing device that processes
In the image processing device
Line-to-line correction processing that corrects the deviation of the reading position in the sub-scanning direction of the color data, and
With respect to the color data corrected by the interline correction processing, a color shift correction process for correcting a color shift component in the sub-scan direction caused by a factor other than the shift of the reading position in the sub-scan direction for each pixel. To execute,
In the inter-line correction process
At least the decimal part correction processing that corrects the deviation of less than one line by interpolation processing is performed,
In the decimal part correction process, the correction amount of less than one line calculated based on the deviation of the reading position in the sub-scanning direction with respect to the color data of the non-reference color in the color data is larger than the calculated correction amount. Interpolation processing is performed using a correction amount that is smaller than 0 and is larger than 0.
In the color shift correction process, correction is performed using a color shift correction amount obtained by adding the remaining correction amount of the calculated correction amount that was not corrected in the decimal part correction process to the correction amount corresponding to the color shift component. Do, do
A computer program characterized by that.

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