JP3700456B2 - Color image processing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color image processing apparatus mounted on a color copying machine or the like, and relates to a color image processing apparatus with improved reproducibility of black characters and black thin lines.
[0002]
[Prior art]
In a conventional color image processing apparatus, for a plurality of image data (R, G, B) having different wavelength components read by a reading means including a CCD sensor, it is determined whether the target pixel is an edge portion of a black line (or black character). Generally, it is determined, and if so, image processing such as edge enhancement is performed. By this image processing, the reproduction quality of black thin lines and black characters included in the color image is improved. The image processing will be briefly described below.
[0003]
First, the color image data obtained by reading a document is passed through a primary differential filter and a secondary differential filter, thereby discriminating an edge portion. Further, a black line or black character black region is determined from the R, G, B color image signals as described below. From these determination results, the black edge portion (edge portion and black region) is determined. Further, it is possible to determine whether the output is the outside (background side) or the inside (on the black region) of the edge depending on whether the output of the secondary differential filter is positive or negative. In the following description, the outer side of the black edge is referred to as an outer black edge portion, and the inner side of the edge is referred to as an inner black edge portion.
[0004]
In order to improve the reproduction quality of black characters or black thin lines, the following processing is performed on the black inner edge portion and the black outer edge portion. For the pixels in the black inner edge portion, an edge enhancement process for adding a lightness edge component to the black component image data Bk is performed. Further, the color component image data C (cyan), M (magenta), and Y (yellow) are not subjected to edge enhancement processing, and have the smallest value in the 5 × 5 or 3 × 3 pixel matrix ( That is, a process of replacing the image data of the target pixel with the pixel data having the lowest density is performed.
[0005]
For pixels outside the black edge, edge enhancement is not performed on the image data Bk, C, M, and Y of the black component and the color component, and the smallest value in the 5 × 5 or 3 × 3 pixel matrix. The pixel data of the target pixel is replaced with the pixel data.
[0006]
By such processing, the C, M, and Y color components are suppressed in the vicinity of the edge of the black character or black thin line in the original image, and the black inner edge is enhanced, thereby improving the reproducibility of the black character or black thin line.
[0007]
As described above, the determination unit for the black edge portion includes the edge determination unit for determining whether or not the target pixel is in the edge portion, and the saturation determination unit for determining whether or not the target pixel is in the black (achromatic) region. Become. Then, the saturation determination unit obtains the difference between the maximum value and the minimum value of the color image signals of R, G, and B as the saturation value, while setting the minimum value as the brightness value, and a threshold value corresponding to the brightness value If the saturation value is smaller, it is determined that the region is an achromatic black region (black line or black character).
[0008]
[Problems to be solved by the invention]
However, the conventional saturation determination unit can accurately determine the black region when the balance between the three primary colors (R, G, B) is lost due to the influence of aberration in the optical system and correction between lines. was difficult. Such a phenomenon is particularly likely to occur with fine lines. For example, black fine lines or black characters of 1 or 2 dots are not correctly determined as achromatic colors, and reproducibility is deteriorated.
[0009]
FIG. 6 shows how a difference occurs between the MTFs (optical transfer functions) of R, G, and B due to the aberration of the optical system. When a black image is read, the MTFs of R, G, and B are ideally equal, but in reality, the defocus amount (out-of-focus) of the optical system is caused by the difference in spectral wavelength of each color of R, G, and B. The MTF curve for shifts for each of R, G, and B. Then, as shown in FIG. 6, when the focus plane is adjusted so that the defocus amount of the G image data becomes zero, the RTF and B MTF values, and consequently the density values, are lowered as a result.
[0010]
Based on FIG. 7 and FIG. 8, the manner in which the balance between the R, G, and B densities is lost due to the interline correction will be described. FIG. 7 is a diagram showing a positional deviation between the R, G, and B lines of the CCD. FIG. 8 shows an example in which the peak value BP of the B signal (image data) is reduced to BP ′ by the interpolation processing of the interline correction unit. It is a figure which shows typically the phenomenon which falls and the difference with the peak value GP of G signal (image data) arises.
[0011]
In a CCD line sensor called a reduction type, as schematically shown in FIG. 7, R, G, and B element rows are arranged at a predetermined pitch in the sub-scanning direction. This pitch corresponds to, for example, four lines when the enlargement / reduction magnification is 1. Normally, since the original surface is scanned in the order of R, G, and B, the G signal is delayed by 4 lines and the B signal is delayed by 8 lines with respect to the R signal.
[0012]
In this case, the inter-line correction unit performs inter-line correction that delays the G signal by four lines with respect to the B signal and further delays the R signal by four lines (eight lines with respect to the B signal). As a result, the phases of the R, G, and B image data are aligned.
[0013]
However, when the enlargement / reduction ratio is not an integer multiple, the delay amount is not equal to the integer line and a fraction is generated. For example, as shown in FIG. 7, when the enlargement / reduction ratio is 0.7, the G signal is delayed by 2.8 lines and the B signal is delayed by 5.6 lines with respect to the R signal. As described above, when a delay corresponding to a decimal line occurs, a delay corresponding to a decimal line is artificially performed by interpolation processing in addition to the delay corresponding to the integer line.
[0014]
For example, when the G signal is delayed by 5.6 lines with the B signal as a reference, the data delayed by 5.6 lines by the interpolation process between the data delayed by 5 lines and the data delayed by 6 lines is performed. Generate. Actually, in order to avoid the conspicuous G signal from being changed by the interpolation processing, interpolation processing is often performed on the B signal with respect to the decimal line for the G signal. As a result, as shown in FIG. 8, the peak value BP of the B signal is reduced to BP ′ by the interpolation process, and a difference from the peak value GP of the G signal is generated. Similarly, the peak value of the R signal is lowered by the interpolation process, and a difference from the peak value of the G signal is generated.
[0015]
As described above, when the density balance between the reference G image data and the other R or B image data is lost due to the aberration in the optical system or the effect of correction between lines, the maximum value as described above is obtained. It becomes difficult to accurately determine whether the color is chromatic or achromatic based on the difference (saturation value) from the minimum value. As a result, the edge enhancement processing of 1 or 2 dots of black fine lines or black characters is not performed, and the lines are printed as greenish lines.
[0016]
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a color image processing apparatus with improved black thin line or black character reproducibility.
[0017]
[Means for Solving the Problems]
The device according to the invention of claim 1 is read by the reading means. Multiple Different Consists of wavelength components To image data Can Based on the signal from the fine line discriminating unit and the thin line discriminating unit that discriminates whether or not the pixel of interest is a thin line, when the pixel of interest is a thin line, the pixel of interest At least one of the image data of the plurality of wavelength components constituting the pixel of interest in order to reduce the difference in density between the image data of the plurality of wavelength components constituting the pixel A density correction unit that performs correction to increase the density of the image data of the wavelength component, and a saturation determination unit that determines whether the pixel of interest is a chromatic color or an achromatic color using the output value of the density correction unit.
[0018]
Preferably, the thin line discriminating unit detects a high density thin line having a width of 1 or 2 dots. In addition to determining whether the pixel of interest is chromatic or achromatic using the output value of the density correction unit, the print image data generation unit prints using the output value of the density correction unit (image data after correction). It is also preferable to generate image data for use.
[0019]
In the apparatus according to the fourth aspect of the invention, the density correction unit performs correction for increasing the density of image data of other wavelength components excluding the wavelength component having the best MTF characteristics. For example, when the reference of the optical system is adjusted to the wavelength of G, the MTF characteristic of the reference G wavelength component is the best, so correction is not performed for the G image data, and only the R and B image data is corrected. , Correction to increase the density.
[0020]
In the apparatus according to the fifth aspect of the invention, the line sensor included in the reading unit includes a plurality of element rows having different wavelength components arranged apart from each other in the sub-scanning direction, and is caused by a positional deviation between the plurality of element rows. And an inter-line correction unit that corrects a phase shift between the image data of the plurality of wavelength components, and the density correction unit is configured to correct the wavelength component image data to be interpolated during correction by the inter-line correction unit. , Correction to increase the density. For example, as described in the related art, when the interline correction unit performs interpolation processing on R and B image data with reference to G image data, the G image data is not corrected, and R and B For only the image data, correction for increasing the density is performed.
[0021]
In the apparatus according to the invention of claim 6, the density correction unit is ,note Eye pixel black A first density correction amount when the fine line discriminating unit discriminates that it is a fine line; ,note Eye pixel Other than black Switch the second density correction amount when the fine line discriminating unit discriminates that it is a fine line Increase the density of image data of at least one wavelength component Correction is executed, and the second density correction amount is set smaller than the first density correction amount.
[0022]
In the present specification, the term “black thin line” usually includes black thin lines and black characters.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 5 is a diagram showing a schematic configuration of a digital color copying machine to which the color image processing apparatus of the present invention is applied.
[0024]
In FIG. 5, the digital color copying machine 100 is composed of an image reading device (reading means) 110 disposed at the upper portion and an image recording device 120 disposed at the lower portion. The image reading device 110 includes a manually placed document reading device 116 and a document panning device 117.
[0025]
The image reading device 110 irradiates the original with light from the light source 111 and forms an image of reflected light from the original surface on the CCD 114 that is a linear image sensor via a reduction optical system including a mirror 112 and a lens 113. The CCD 114 converts an image of a document into an analog signal by photoelectric conversion and charge transfer. For example, the resolution of the CCD 114 is 400 dpi, and the maximum document size is A3. In this case, one line in the main scanning direction is about 5000 dots.
[0026]
The analog signal output from the CCD 114 is given to the image processing device 115. The image processing device 115 converts the analog signal into digital data, performs image processing such as scaling and image quality correction, and outputs the processed digital data from the image reading device 110 as digital image data.
[0027]
Scanning in reading a document is performed with the scanning direction of the elements constituting the CCD 114 (longitudinal direction of the CCD 114) as the main scanning direction and the direction perpendicular thereto as the sub-scanning direction. The sub-scanning direction is performed by moving the mirror 112 in the horizontal direction in the case of a manually placed document, and is performed by transporting the document in the case of document panning. In either case, the image signal is sequentially transferred for each line in the main scanning direction.
[0028]
The image recording device 120 converts the digital image data output from the image reading device 110 into an analog signal by the laser diode driving unit 121, further converts it into light by the laser diode 122, and passes through the polygon mirror 123 to the photosensitive drum 124. To form an image. The current input to the laser diode 122 is controlled, and the amount of light is controlled in units of pixels. As a result, a latent image is formed on the photosensitive drum 124, which is developed with toner and then transferred to the recording paper 125. In this manner, an image with 400 dpi and 256 gradations is formed by electrophotography.
[0029]
FIG. 1 is a block diagram showing the overall configuration of an image processing apparatus 115 according to an embodiment of the present invention.
In FIG. 1, analog signals output from the CCD 114, that is, color image signals of R, G, and B colors are input to the A / D converter 13. The A / D converter 13 converts an R, G, B color image signal that is an analog signal into R, G, B color image data that is 8-bit digital data (256-gradation density data). The obtained R, G, B color image data is input by the shading correction unit 14 to the interline correction unit 15 after being subjected to shading correction for correcting unevenness in the amount of light in the main scanning direction.
[0030]
The interline correction unit 15 is a circuit that corrects the phase shift of the R, G, B color image signals (data) caused by the positional shift between the R, G, B lines of the CCD 114.
FIG. 2 is a block diagram showing a schematic configuration of the interline correction unit 15.
[0031]
The interline correction unit 15 includes line delay circuits 31 to 33, FIFO (line memories) 34 and 36, and interpolation circuits 35 and 37. As described in the prior art, the line delay circuits 31 to 33 delay the R image data and the G image data by integer lines with respect to the B image data. Also, the FIFOs 34 and 36 and the interpolation circuits 35 and 37 perform the fractional delay corresponding to the decimal line by interpolation processing. The interpolation process is performed only for the R and B image data with the conspicuous G image data as a reference.
[0032]
The R, G, B color image data in which the phase shift is corrected by the interline correction unit 15 is subjected to chromatic aberration correction by the chromatic aberration correction unit 16 and further includes a magnification / movement processing unit 17 including a magnification line memory. Then, after being subjected to enlargement / reduction processing in the main scanning direction in accordance with the variable magnification, it is input to the area determination unit 21.
[0033]
As will be described in detail later with reference to FIG. 3, the region determination unit 21 includes a thin line determination unit 41, a density correction unit 42, and a saturation determination unit 43. The region discriminating unit 21 discriminates whether or not the target pixel is a fine line. If the target pixel is a thin line, the region discriminating unit 21 performs correction to increase the density of the R and B image data and outputs the correction to the color conversion unit 18.
[0034]
The area discriminating unit 21 includes an edge discriminating unit and a halftone discriminating unit (not shown). The edge determination unit outputs a determination signal EDGE indicating that the target pixel is an edge portion of the image. A determination signal AMI indicating that the target pixel is a halftone image is output from the halftone determination unit. If the saturation determination unit 43 determines that the region is a black region and the edge determination unit determines that the region is an edge portion, the pixel of interest is determined to be a black edge, and the determination signal BKEDG is set to MTF. Output to the correction unit 20.
[0035]
The color conversion unit 18 adjusts the color image data R, G, and B. The color correction unit 19 converts CMY (subtractive color) printing color image data C (cyan), M (magenta), Y (yellow), and Bk (black) from RGB (additional color) color image data. Generate. The generated color image data for printing C, M, Y, Bk is given to the MTF correction unit 20.
[0036]
The MTF correction unit 20 performs image processing such as edge enhancement on the area determined to be a black edge based on the determination signal BKEDG from the area determination unit 21. The region discriminating unit 21 may also discriminate the halftone dot region, and the MTF correcting unit 20 may perform image processing such as smoothing based on the discrimination signal. The color image data for printing C, M, Y, Bk output from the MTF correction unit 20 is given to the image recording device 120.
[0037]
FIG. 3 is a block diagram illustrating a part of the configuration of the area determination unit 21.
In FIG. 3, an area discriminating unit 21 is a thin line discriminating unit 41 that discriminates a black thin line or another color thin line, and one of R and G image data based on signals RBEN, REN, and BEN that are the discrimination results. Or a density correction unit 42 that increases both densities, and a saturation determination unit 43 that determines whether the pixel of interest is a chromatic color or an achromatic color based on the R, G, and B image data after density correction. .
[0038]
The fine line discriminating unit 41 has line memories 44, 46, and 48 for delaying each line of R, G, and B image data by one line, and line memories 45, 47, and 49 for delaying by two lines. In addition, for each of the R, G, and B image data, a peak detection unit that detects the presence or absence of a peak based on three types of data: image data with zero delay amount, data delayed by one line, and data delayed by two lines 50, 51, 52.
[0039]
For example, the peak detection unit 50 for R image data detects the presence or absence of a peak in the horizontal direction from the image data for three lines, that is, the change in the pixel of interest and the image data before and after the target pixel. Set RHP to L (low) level. When there is no peak, the output signal RHP is set to the H (high) level. In addition, in the image data delayed by one line where the pixel of interest exists, the presence or absence of a peak in the vertical direction is detected from the change in the pixel of interest and the image data before and after (up and down), and if there is a peak, the output signal RVP is Set to L level. When there is no peak, the output signal RVP is set to H level.
[0040]
Similarly, for the peak detector 51 for G image data and the peak detector 52 for B image data, if there is a horizontal peak, the output signal GHP or BHP is set to L level, and if there is no peak, the output signal GHP or BHP is set to H level. Level. If there is a peak in the vertical direction, the output signal GVP or BVP is set to L level, and if there is no peak, the output signal GVP or BVP is set to H level.
[0041]
Detecting the presence or absence of a peak as described above corresponds to detecting whether or not a thin line has a width of 1 dot. Note that it is also possible to detect whether or not the line is a thin line having a width of 2 dots by enlarging changes before and after the pixel of interest up to 5 lines (5 dots) and performing peak detection.
[0042]
A total of six outputs RHP, RVP, GHP, GVP, BHP, and BVP obtained by detecting the three peak detection units 50, 51, and 52 in the horizontal direction and the vertical direction are input to the logic operation unit 53. . The logical operation unit 53 performs the following logical operation on these six data to obtain three outputs RBEN, REN, and BEN.
[0043]
First, the output RBEN is L level when all the R, G, B image data (all wavelength components) have a peak in the horizontal direction or the vertical direction, and is H level in other cases, and is expressed by the following logical expression. The
[0044]
RBEN = [(RHP + GHP + BHP). (RVP + GVP + BVP)]
If the signal RBEN is at L level, it means that there is a high possibility that the target pixel is a black thin line.
[0045]
The output REN is at the L level when the R image data has a peak in the horizontal direction or the vertical direction and RBEN is not at the L level, and at the H level otherwise. In other words, not all the wavelength components, but at least when the R component has a peak, it is at the L level, otherwise it is at the H level, and is represented by the following logical expression. If the signal REN is at the L level, it means that there is a high possibility that the target pixel is not a black thin line but a thin line of a color including red.
[0046]
REN = (RHP ・ RVP + RBEN)
The output BEN is L level when the B image data has a peak in the horizontal direction or the vertical direction and RBEN is not at the L level, that is, not all wavelength components but at least the B component has a peak. Otherwise, it is at the H level and is represented by the following logical expression. When the signal BEN is at the L level, it means that there is a high possibility that the target pixel is not a black thin line but a thin line of a color including blue.
[0047]
BEN = (BHP ・ BVP + RBEN)
The three determination signals RBEN, REN and BEN obtained as described above are given to the density correction unit 42. The density correction unit 42 also receives R, G, and B pixel data for the pixel of interest. Based on the three determination signals RBEN, REN, and BEN, the density correction unit 42 performs correction for increasing the density of both or one of the R and B pixel data. The state of density correction by the density correction unit 42 is shown in FIG.
[0048]
That is, in FIG. 9, the left side is before correction, and the right side is after correction. In this example, there is no change in the density of the G pixel data before and after the correction, but the density of the R and B pixel data is increased by the correction. Before the correction, the density of the R and B pixel data and the density of the G pixel data are greatly different from each other, so that it is easy to be misidentified as a color character. However, after the correction, the density of the R and B pixel data is It approaches the density of the G pixel data, and it becomes easy to recognize that it is a black thin line or a black character. Next, an example of the configuration of the density correction unit 42 will be described.
[0049]
FIG. 4 is a block diagram illustrating an example of the configuration of the density correction unit 42.
In FIG. 4, the density correction unit 42 includes multipliers 60 and 62 and selectors 61 and 63 for increasing the density of the R image data. Similarly, multipliers 64 and 66 and selectors 65 and 67 for increasing the density of the B image data are provided. Since the G image data is reference data, it is output as it is without performing density correction.
[0050]
The following description will be made on the density correction of the R image data, but the same applies to the density correction of the B image data. First, the first multiplier 60 obtains a product of R image data as an A input and RM1 as a B input. RM1 is a first density correction coefficient and is set to a value larger than 1. The first selector 61 selects the R signal as the A input or the output of the multiplier 60 as the B input according to the value of RBEN that is the S input. If RBEN is at L level, the output of multiplier 60, that is, the R signal after density correction is selected, and if RBEN is at H level, the R signal before density correction is selected.
[0051]
The second multiplier 62 calculates the product of the output of the selector 61 that is the A input and RM2 that is the B input. RM 2 Is a second density correction coefficient, greater than 1 and RM 1 Set to a smaller value. The second selector 63 selects the output of the selector 61 that is the A input or the output of the multiplier 62 that is the B input according to the value of the REN that is the S input. If REN is at the L level (in this case, RBEN is always at the H level as described above), the output of the multiplier 62, that is, the R signal after density correction by the second multiplier 62 is selected. RE If N is H level, the output of the selector 61, that is, the R signal before density correction or the R signal after density correction by the first multiplier 60 is selected.
[0052]
The first multiplier 60 performs correction to increase the density of the R signal when RBEN is at L level, that is, when a black thin line is detected, and the second multiplier 62 performs correction when REN is at L level, that is, , Correction is performed to increase the density of the R signal when a thin color line including red is detected. In copying a manuscript, normally, black character reproducibility is more important than color reproducibility. In addition, when it is detected that only one or two wavelength components have a peak, there is a higher possibility of erroneous detection due to the influence of noise than when all wavelength components are detected to have a peak. Therefore, as described above, the correction coefficient RM2 (that is, the density correction amount when the black thin line is detected) of the second multiplier 62 is included in the correction coefficient RM1 of the first multiplier 60 (that is, red is included). It is set smaller than the density correction amount when a fine color line is detected.
[0053]
The operations of the multipliers 64 and 66 and the selectors 65 and 67 for correcting the density of the B image data are the same as the operations of the multipliers 60 and 62 and the selectors 61 and 63 for correcting the density of the R image data. It is the same. Also in this case, for the above reason, the correction coefficient BM2 of the second multiplier 66 is set smaller than the correction coefficient BM1 of the first multiplier 64.
[0054]
The density-corrected R, G, B image data output from the density correction unit 42 is input to the saturation determination unit 43 as shown in FIG. As described in the section of the prior art, the saturation determination unit 43 obtains the difference between the maximum value and the minimum value of the R, G, B image data as the saturation value, and the brightness value (R, G, B image data). If the saturation value is lower than the threshold value determined in accordance with (minimum value), it is determined that the color is an achromatic color (black region), and a determination signal BKAREA is output. If the determination signal BKAREA is at the L level, it indicates that the black region is determined.
[0055]
As described above, the determination signal BKARE is logically ANDed with the determination signal of the edge determination unit, and is output from the region determination unit 21 as the black edge determination signal BKEDG shown in FIG. Given to. In addition, the R, G, B image data output from the density correction unit 42 of the area determination unit 21 is supplied to the saturation determination unit 43, and R, G, B image data after density correction (however, G The image data is output from the area discriminating unit 21 as no density correction).
[0056]
As shown in FIG. 1, the R, G, and B image data after density correction pass through a color conversion unit 18 and a color correction unit 19 (print image data generation unit), and print image data C, M, and Y , Bk.
[0057]
In the embodiment described above, the configuration, processing contents, processing order, and the like of the entire region determination unit 21, the image processing device 115, and other units or each unit can be appropriately changed in accordance with the spirit of the present invention.
[0058]
【The invention's effect】
According to the present invention, it is determined whether or not the target pixel is a thin line. In order to reduce the difference in density between the image data of the plurality of wavelength components constituting the pixel of interest, at least one of the image data of the plurality of wavelength components constituting the pixel of interest Since correction is performed to increase the density of image data of wavelength components (for example, R and B), even when the density balance between R, G, and B is lost due to the influence of aberration in the optical system or correction between lines, the density balance Can be recovered, and the saturation determination unit can accurately determine the black region. As a result, processing such as edge enhancement of the black thin line is correctly performed, so that the reproducibility of the black thin line or the black character is improved.
[0059]
According to the invention of claim 3, since the print image data generation unit generates the image data for printing based on the image data after the density correction, the black reproducibility in the black thin line or the black character region is further improved.
[0060]
According to the invention of claim 6, when a fine line of a color other than black (R or B) is detected, the correction amount for increasing the density of the color is set as the density of R and B when the black fine line is detected. By setting the correction amount smaller than the correction amount, priority is given to the black reproducibility and the influence of noise can be reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram of a color image processing apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram showing an internal configuration of an interline correction unit.
FIG. 3 is a block diagram illustrating a part of an internal configuration of an area determination unit.
FIG. 4 is a circuit diagram showing an internal configuration of a density correction unit.
FIG. 5 is a diagram showing a schematic configuration of a digital color copying machine.
FIG. 6 is a diagram illustrating a state in which a difference occurs between R, G, and B MTFs due to aberration of the optical system.
FIG. 7 is a diagram showing a positional shift between R, G, and B lines of a CCD.
FIG. 8 is a diagram schematically illustrating a phenomenon in which a peak value of B image data is lowered and a difference from a peak value of G image data is generated by the interpolation processing of the interline correction unit.
FIG. 9 is a diagram illustrating a state of density correction by a density correction unit.
[Explanation of symbols]
15 Line correction unit
18 color converter
19 color correction unit (print image data generation unit)
20 MTF correction unit
21 Area discriminator
41 Fine line discriminator
42 Density correction unit
43 Saturation Discriminator
44-49 line memory
50 to 52 Peak detector
53 Logical operation part
60, 62, 64, 66 multiplier
61, 63, 65, 67 selector
114 CCD (line sensor)
115 Image processing apparatus
RM1, BM1 first density correction coefficient
RM2, BM2 Second density correction coefficient

Claims (6)

A thin line determination unit that the pixel of interest definitive the image data composed of a plurality of different wavelength components read by the reading means to determine whether thin lines,
Based on a signal from the thin line determination unit, when the target pixel is a thin line, a plurality of pixels constituting the target pixel are configured to reduce a difference in density between image data of a plurality of wavelength components constituting the target pixel. A density correction unit that performs correction to increase the density of the image data of at least one wavelength component of the image data of the wavelength component;
A color image processing apparatus comprising: a saturation determination unit that determines whether a pixel of interest is a chromatic color or an achromatic color using an output value of the density correction unit. The fine line discriminating unit detects a high-density thin line having a width of 1 or 2 dots.
The color image processing apparatus according to claim 1. A print image data generation unit that generates image data for printing using the output value of the density correction unit;
The color image processing apparatus according to claim 1. The density correction unit performs correction for increasing the density of image data of other wavelength components excluding the wavelength component having the best MTF characteristics.
The color image processing apparatus according to claim 1. In the line sensor included in the reading unit, a plurality of element rows having different wavelength components are arranged separately in the sub-scanning direction,
An inter-line correction unit that corrects a phase shift between the image data of the plurality of wavelength components due to a positional shift between the plurality of element rows;
The density correction unit performs correction for increasing the density of the image data of the wavelength component to be interpolated during correction by the interline correction unit.
The color image processing apparatus according to claim 1. The density correction unit includes a first density correction amount when the attention pixel is the thin line determination unit has determined that the black thin lines, and the thin line determination unit attention pixel is a color thin line other than black The correction is performed by switching the second density correction amount at the time of determination to increase the density of the image data of the at least one wavelength component , and the second density correction amount is greater than the first density correction amount. Set to small,
The color image processing apparatus according to any one of claims 1 to 5.

Images