JP2001313840A - Image-processing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image-processing unit that can properly reproduce a colored part of a low density region. SOLUTION: A MIN data detection section 31 and a MAX data detection section 32 respectively detect a minimum value min (C, M, Y) of color image data C, M, Y and a maximum value max (C, M, Y) of the color image data C, M, Y separated in three primary colors. A saturation detection section 33 calculates the difference between them as saturation information ci. By dividing a difference between the minimum value min (C, M, Y) and the maximum value max (C, M, Y) by the maximum value max (C, M, Y) corresponding to the color reproduction range, a saturation parameter (c) is obtained, and a UCR rate A is decided by a UCR rate table 35 on the basis thereof. The saturation parameter (c) has a large value, even in a low-density region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus applied to a color digital copying machine or the like.

[0002]

2. Description of the Related Art Generally, in an electrophotographic color digital copying machine, reflected light from an illuminated color original is red.
CCD through color separation filters of (R), green (G) and blue (B)
By receiving light with a photoelectric conversion element such as a red (R) component,
After color separation into light receiving signals R, G, and B proportional to the light intensities of the green (G) component and the blue (B) component, A / D conversion into digital values, and cyan, which is color image data proportional to density,
(C), an image reading unit for converting the density into magenta (M) and yellow (Y) is provided. The obtained color image data C,
Black generation processing for generating black data k using M and Y is performed, and under color removal (UCR: Un) is performed using the generated black data k.
der Color Removal).

As described above, by performing the black generation processing and the undercolor removal and replacing a part of the color image data C, M, and Y with the black data, the consumption of the color toner can be reduced, and the shadow parts and characters can be removed. The reproducibility is improved. Further, by using the black toner, an achromatic color can be expressed favorably, and the contrast of an image can be improved. Further, since a gray image can be represented by one color of black, the stability of the expression of the gray image can be maintained. Furthermore, since the black toner is inexpensive compared to the color toner, the color toner can be saved, and there is also an advantage that the running cost can be reduced.

Since the color is black when the values of the color image data C, M, Y are equal, the black data K determines the minimum value min (C, M, Y) of the color image data C, M, Y. And is obtained by the following equation (1). A is called the UCR rate,
Set to a constant value. K = A · min (C, M, Y) (1) However, in this general undercolor removal, the color is reduced in an achromatic portion of an image (particularly a character portion requiring sharpness). Bleeding occurs due to the toner, and excessive black data K is set in a chromatic portion (particularly a green portion or a skin color portion in which roughness is conspicuous). Or may be.

To solve this problem, Japanese Patent Laid-Open No.
No. 233928 discloses that UC and chromatic portion
A method for setting different R rates is disclosed. In this prior art, the black data K is calculated by the following equation (2).
Is determined.

[0006]

(Equation 2)

That is, by using the equation (2), the maximum value max (C, C,
M, Y) and the minimum value min (C, M, Y) can be prevented from using an excessive amount of black toner in a chromatic portion where the difference is large. On the other hand, the maximum value max (C, M,
In the achromatic portion where the difference between Y) and the minimum value min (C, M, Y) is small, a large UCR ratio A (the portion in [] in the above equation (2)) is set. Thereby, an appropriate UCR rate A can be set in the chromatic color part and the achromatic color part.

[0008]

One problem of this prior art is that it is not possible to express chromatic colors well in low density areas such as highlights of an image. That is, in the low-density area, the maximum value max (C, M, Y) of the color image data C, M, Y becomes smaller, so that the maximum value max (C, M, Y) and the minimum value min (C ,
M, Y) also decreases accordingly. as a result,
There is a problem that the UCR ratio A becomes relatively large, and a large amount of black toner is mixed into the low-density chromatic portion.

It is an object of the present invention to solve the above-mentioned technical problems and to provide an image processing apparatus capable of favorably reproducing a chromatic portion in a low density area.

[0010]

According to the first aspect of the present invention, there is provided an image processing apparatus for processing image data which has been separated into a plurality of colors for each pixel of an input image. An image processing apparatus for detecting saturation information ci based on image data of a plurality of colors;
2, 33, 33A) and a color gamut detection means (3) for obtaining a color gamut r based on the image data of a plurality of colors.
2, 32A) and a black generation unit (3) that generates a black output value Bk using a saturation parameter c expressed by the following equation (A).
4, 34A, 35, 36, 37).

C = ci / (r · β) (A) where β is a constant. Note that the alphanumeric characters in parentheses following the component names indicate the codes of the corresponding components in the embodiments described later. Hereinafter, the same applies in this section. According to the present invention, the saturation information ci is divided by the color reproduction range r, and the black generation processing is performed using the saturation parameter c obtained thereby. The color reproduction range r can be represented, for example, by the maximum value max of the image data of a plurality of colors. That is, the color reproduction range r takes a large value in a high density area,
It takes a small value in the low concentration area.

Therefore, in the low concentration region, the above (A)
The value of the denominator of the equation becomes smaller. Therefore, in the low concentration region, even if the value of the numerator in the formula (A) is small,
The saturation parameter c can take a relatively large value. As described above, the saturation parameter c used in the black generation processing is the density (color reproduction range) in the region of interest.
Has an appropriate value according to the following. This allows
Good black generation processing becomes possible. Specifically, black is not excessively mixed into a chromatic highlight portion in a color image, and vivid color reproduction can be achieved.

According to a second aspect of the present invention, a maximum value detecting means (3) for detecting a maximum value max of image data of a plurality of colors.
2) and a minimum value detecting means (31) for detecting a minimum value min of the image data of the plurality of colors, wherein the saturation detecting means obtains the saturation information ci by ci = max-min.
And the color gamut detection means calculates r =
2. The image processing apparatus according to claim 1, wherein a color reproduction range is obtained by max.

In the present invention, the saturation information ci is obtained from the difference between the maximum value max and the minimum value min of the image data of a plurality of colors, and the color reproduction range r is obtained as the maximum value max. As a result, good black generation processing can be realized with a simple configuration for detecting the maximum value max and the minimum value min and subtracting them. The image processing apparatus includes: a maximum value detection unit (32) for detecting a maximum value max of the image data of a plurality of colors; and a minimum value detection unit (31) for detecting a minimum value min of the image data of a plurality of colors. May be further included. In this case, the above-mentioned saturation detecting means uses ci =
It is preferable that the saturation information ci is obtained from max-min-α (where α is a constant). In this case, it is preferable that the color gamut detection means obtains the color gamut by r = max−α or r = max.

In the case of the present invention, the value of the constant α is set substantially equal to the difference between the maximum value max and the minimum value min when the achromatic image is read by the image reading means (1). preferable. By adopting such a configuration,
It is possible to compensate for a color shift that occurs when each pixel is read out by color separation by the image reading unit. When an achromatic image is read by the image reading means, max-min is not always zero. In such a case, color bleeding occurs particularly in a black thin line portion such as a character portion. According to the present invention, since the saturation information ci can be set to zero in the achromatic color portion, appropriate black data K can be generated, so that color misregistration can be effectively prevented.

According to a third aspect of the present invention, the black generating means determines black data K in accordance with the following equation (B).
3. The image processing apparatus according to claim 1, wherein the black output value Bk is generated based on the black data K. K = (b−a · c) · min (B) where a and b are positive constants.

The saturation parameter c obtained by the above equation (A) is small in an achromatic portion and large in a chromatic portion. Therefore, the black data K obtained by the above equation (B) takes a large value in an achromatic color portion and takes a small value in a chromatic color portion. This makes it possible to set large black data K in the achromatic part while preventing black from being mixed in the chromatic part. Thereby, the black portion can be reproduced well. The invention according to claim 3 may be realized by the black generation means including a black output value table (37) that receives the black data K as an input and outputs a black output value Bk.

Further, the UC is obtained by inputting the saturation parameter c.
A UCR rate table (35) that outputs the R rate A (= ba-c) may be used. Of course, instead of using a table, an operation corresponding to the above equation (B) may be performed. The image processing device is configured to perform the following based on the black data K:
The image processing apparatus may further include a color correction unit (24) that performs undercolor removal processing for subtracting data corresponding to an achromatic component from the color image data and outputs corrected color image data.

The black data K obtained by the above equation (B)
Uses the saturation parameter c obtained by the expression (A), so that it can have an appropriate value even in a low density region of a chromatic color. Therefore, by performing the under color removal processing based on the black data K, the under color removal processing in the chromatic low density area can be appropriately performed,
Vivid color reproduction becomes possible. The color image data may be color-separated into three primary colors.

[0020]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing an electrical configuration of a color digital copying machine to which an image processing apparatus according to one embodiment of the present invention is applied. The color digital copying machine includes an image reading unit 1, an image processing unit 2, a laser light output unit 3, and an image forming unit 4.

The image reading unit 1 includes an illuminating unit (not shown) for illuminating a color document to be copied, a photoelectric conversion unit 11, and a density conversion unit 12, and reads a color document to read color image data C, M, and C. Y is output. Image processing unit 2
Are an input processing unit 21, an image type determination unit 22, a black generation processing unit 23, a color correction processing unit 24, and an output color selection unit 25
, A scaling unit 26, a spatial filter unit 27, a gradation processing unit 28, and an output control unit 29. The color image data C, M, and Y obtained by the image reading unit 1 will be described later. That is, predetermined processing is performed.

The laser beam output unit 3 irradiates a laser beam on the photosensitive member of the image forming unit 4 which has been charged in advance in accordance with the color image data processed by the image processing unit 2, and electrostatically charges the surface of the photosensitive member. This is to form a latent image. The image forming unit 4 includes a photoconductor, a developing device, a transfer paper transport device, a fixing device, and the like (not shown). The electrostatic latent images formed for the respective colors on the photoconductor surface are sequentially converted to cyan (C), magenta, and magenta. (M) and yellow
The toner is developed using the color toner (Y) and the black (Bk) toner, transferred to the transfer paper conveyed to the photoconductor, and
The transfer toner image formed by transferring the color toner is fixed on the transfer paper.

The photoelectric conversion unit 11 of the image reading unit 1 is composed of a large number of CCDs or the like arranged in a line, and reflects reflected light from a minute area (hereinafter, referred to as "pixel") of a illuminated color document. A photoelectric conversion element for receiving light, and R, G, and B filters disposed on the optical path of the reflected light for separating colors into red (R), green (G), and blue (B), which are three primary colors of additive color mixture. , An A / D converter, and photoelectrically converts three primary color analog color image signals proportional to the light intensities of the red (R) component, the green (G) component, and the blue (B) component. The signal is converted into digital color image data R, G, B having a predetermined number of bits (8 bits in the present embodiment).

The density conversion unit 12 outputs color image data R,
G and B are complementary colors of cyan (C) and magenta, respectively.
(M), yellow (Y), that is, color image data C, M, and Y proportional to the density of the three primary colors in the subtractive color mixture. The input processing unit 21 of the image processing unit 2 performs processing such as frequency conversion of a reference clock frequency when transmitting each of the color image data C, M, and Y. The difference from the reference clock frequency in the image processing unit 2 is absorbed.

After performing the above processing, the input processing section 21 converts the color image data C, M, and Y into FIFOs, respectively.
(First In First Out) are stored in the memories M1, M2, M3. The image type determination unit 22 includes a line memory 221 capable of holding a plurality of lines of color image data, and reads each of the plurality of lines of color image data C, M, and Y stored in the FIFO memories M1, M2, and M3. The color image data of interest is stored in the line memory 221, and the color image data of interest belongs to any one of the character area, the photograph area, and the halftone dot area by using the color image data of a plurality of lines stored in the line memory 221. Is determined.

The image type discriminating section 22 performs this discrimination by using a known method described in Japanese Patent Application Laid-Open No. 8-149298 or the like, and outputs the discrimination result to a black generation processing section 23 and a color correction processing section 24. , A scaling unit 26, a spatial filter unit 27,
It is sent to the gradation processing unit 28 and the output control unit 29.
Further, the image type discriminating section 22 includes FIFO memories M1, M
2, the color image data C of the same pixel stored in M3,
M and Y are read synchronously and sent to the black generation processing unit 23.

The black generation processing section 23 generates black image data Bk using the color image data C, M, and Y. The color correction processing section 24 generates a gray component corresponding to the black image data Bk. The color image data C, M, and Y are corrected by reducing the data. The output color selection unit 25 selects and outputs one of the image data C, M, Y, and Bk. Magnification processing unit 2
6 performs processing such as enlargement or reduction of the selected image data according to a set magnification or the like.

The spatial filter unit 27 is provided with an image type discriminating unit 2
Known filter processing such as edge enhancement processing and smoothing processing is performed in accordance with the determination result obtained in step 2 above. Edge enhancement processing is performed for a character area, and smoothing processing is performed for a photographic area and a halftone dot area. The gradation processing unit 28 performs known halftone processing such as dither processing and multi-value dither processing.
The output control unit 29 controls the emission of the laser light from the laser light output unit 3 according to the image data sent from the gradation processing unit 28.

FIG. 2 is a block diagram showing the configuration of the black generation processing section 23 and the color correction processing section 24. The black generation processing unit 23 is configured by a logic circuit, compares color image data C, M, and Y of the same pixel, and determines and extracts the minimum value min (C, M, Y) of the MIN data. The color image data C,
M and Y are compared, and the maximum value max (C, M,
Y), and a MAX data detection unit 32 for determining and extracting Y). The minimum value mi sent by the MIN data detector 31
The n (C, M, Y) and the maximum value max (C, M, Y) transmitted by the MAX data detection unit 32 are input to the saturation detection unit 33.

The saturation detector 33 calculates the maximum value max (C, M,
And a subtractor for subtracting the minimum value min (C, M, Y) from Y), and the saturation information ci (= max (C, M, Y)
-Min (C, M, Y)) is output. The detected saturation information ci is input to the saturation parameter calculation unit 34. The saturation parameter calculator 34 further includes a maximum value max (C,
M, Y). Saturation parameter calculator 34
Calculates the saturation parameter c according to the following equation (3).

[0031]

(Equation 3)

The value of the constant β is set to an appropriate value according to the area type information provided from the image type discriminating section 22. The saturation parameter c calculated by the saturation parameter calculator 34 is input to the UCR rate table 35. The UCR ratio table 35 is a table that stores the UCR ratio A corresponding to each value of the saturation parameter C. UC output from this UCR rate table 35
The R rate A is provided to a multiplier 36.
The minimum value min (C, M, Y) is input from the MIN data detector 31 to the multiplier 36. The multiplier 36 multiplies the UCR rate A by the minimum value min (C, M, Y) to obtain black data K (= A · min (C, M,
Y)) is generated. The black data K is given to a Bk table 37 for generating a black output value Bk. The Bk table 37 is a table that stores an appropriate black output value Bk corresponding to each value of the black data K.

The components that perform the processing up to this point, that is, the MIN data detection unit 31 and the MAX data detection unit 3
2. Saturation detector 33, saturation parameter calculator 34, UC
R rate table 35, multiplier 36 and Bk table 37
Constitute the black generation processing unit 23. Figure 3 shows the UCR
FIG. 9 is a diagram for explaining the contents of a rate table 35. In FIG. 3, the UCR rate A corresponding to the saturation parameter c represented by 8-bit data of 0 to 255 is expressed as a percentage. That is, actually, the saturation parameter calculation unit 34 uses the value obtained by multiplying the saturation parameter c expressed by the above equation (3) by 255 as the saturation parameter c as the UCR
The UCR rate table 35 given to the rate table 35 uniformly sets the UCR rate A to 100% for a chroma parameter c of 0 to 30. Then, for a saturation parameter c exceeding 30, the UCR follows a straight line of A = b−a · c (where a and b are constants and a and b> 0).
The rate A is set. This prevents a false contour from occurring at the hair growth of a photographic image of a person, and also prevents the black toner from being excessively mixed into the skin color portion. This latter effect is especially true when the UCR rate A is 0 at the saturation parameter c = 100.
% Is set by setting the above-mentioned straight line.

FIG. 4 is a diagram for explaining the contents of the Bk table 37. Three Bk tables 37 are provided corresponding to the character area, the photograph area, and the halftone area.
One of the tables is selected and used according to the determination result from the image type determination unit 22.
However, FIG. 4 illustrates only one of them. As understood from FIG. 4, the black output value Bk is a value substantially proportional to the black data K.

Referring again to FIG. 2, the color correction processing unit 24
Is supplied with black data K from the black generation processing unit 23. The color correction processing unit 24 includes a UCR table 41 for determining achromatic component data to be removed from the color image data C, M, and Y based on the black data K. The UCR table 41 is provided three in correspondence with the character area, the photograph area and the halftone area.
Any one of the three UCR tables 41 is selected and used based on the image type information provided from the image type determination unit 22.

FIG. 5 is a diagram for explaining the contents of the UCR table 41. The UCR table 41 has contents in which a larger UCR amount (undercolor removal amount) is set as the black data K increases. Bk table 37 and UC
By separately providing the R table 41, the generation of the black output value Bk and the conversion of the U from the color image data C, M, Y
The CR amount can be determined independently. This allows U
Even when the CR amount is small, a relatively large black output value Bk can be set.

The UCR amount generated by the UCR table 41 is based on the C data generation unit 42, the M data generation unit 43, and the Y data amount.
The data is supplied to the data generator 44. The C data generation unit 42 outputs the color image data C ′ after the under color removal processing correction is performed by subtracting the UCR amount from the color image data C. Similarly, the M data generation unit 43
And the Y data generation unit 44 outputs the color image data M, Y
, The color image data M ′ and Y ′ subjected to the under-color removal processing are output respectively. These color image data C ', M', Y '
And the black output value Bk from the Bk table 37 is provided to the output color selection unit 25.

As described above, according to this embodiment, the saturation parameter c is determined by the saturation information ci = max (C, M, Y) −
min (C, M, Y) is the maximum value max corresponding to the color reproduction range r
It is obtained by dividing by (C, M, Y). The value of the saturation parameter c does not become too small even in a low density region such as a highlight portion in a color image. That is, in the low concentration region, the maximum value
Since max (C, M, Y) becomes a small value, max (C, M, Y)
Even when (M, Y) -min (C, M, Y) has a small value, the saturation parameter c can have a relatively large value as a whole.

Thus, in the low-density area of the chromatic portion,
Since the UCR rate A takes a relatively large value (see FIG. 4), it is possible to prevent a large amount of black from being mixed into such an area. On the other hand, in an achromatic portion, the saturation parameter c has a small value.
The rate A increases. This makes it possible to express characters and the like satisfactorily, and to effectively save color toner. FIG. 6 is a diagram for explaining the configuration of an image processing apparatus according to the second embodiment of the present invention. A black generation processing unit to be used instead of the black generation processing unit 23 in the configurations of FIGS. 23A is shown.
6, parts corresponding to the respective parts shown in FIG. 2 described above are denoted by the same reference numerals as in FIG.

The read pixels of the image reading section 1 are RGB
Are not always equal. Therefore, even when an achromatic image is read, the maximum value max (C,
M, Y) and the minimum value min (C, M, Y) may not be 0. In this case, the pixel is not reproduced in an achromatic color. Specifically, a so-called color shift occurs in a thin line portion of a character or the like. Therefore,
In this embodiment, the saturation parameter calculation unit 3 used in place of the saturation parameter calculation unit 34 in the configuration of FIG.
4A calculates the saturation parameter c by the following equation (4) instead of the above equation (3).

[0041]

(Equation 4)

More specifically, the saturation detector 33A outputs ci =
The saturation information ci is obtained from max (C, M, Y) -min (C, M, Y) -α. Also, the MAX data detection unit 32
Color reproduction range r based on the maximum value max (C, M, Y)
Is obtained by r = max (C, M, Y) −α, and a color reproduction range detection unit 32A that supplies the obtained value to the saturation parameter calculation unit 34A is provided. The value of the constant α is obtained by reading an achromatic image in advance by the image reading unit 1 and obtaining the maximum value ma obtained at this time.
It is set equal to the difference between x (C, M, Y) and the minimum value min (C, M, Y).

The chroma parameter c obtained by the above equation (4) is such that when an achromatic image is read, its numerator is 0.
Becomes Thereby, the problem of color misregistration can be solved regardless of the input error of the image reading unit 1. That is,
In the achromatic portion, since the saturation parameter c becomes 0, the black data K can take the maximum value (= min (C, M, Y)). Reproduction can be performed only with toner. As a result, it is possible to satisfactorily reproduce a thin line portion such as a black character.

Although the two embodiments of the present invention have been described above, the present invention can be embodied in other forms. For example, in the above embodiment, the saturation parameter c
UCR rate table 3 which outputs UCR rate A by inputting
5 is used, but instead of using the UCR rate table 35, the UCR rate A may be determined by calculating the following equation (5). A = ba-c (5) In the above-described embodiment, the UCR rate A is uniformly set to 100% when the saturation parameter c is 30 or less. Even in a range where c is a small value, the UCR rate may decrease as the value increases.
That is, for example, even when the value of the saturation parameter c is 30 or less, the UCR rate A may be determined according to the following equation (6).

A = 1−a · c (6) In addition, various design changes can be made within the scope of the technical matters described in the claims.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical configuration of a color digital copying machine to which an image processing apparatus according to an embodiment of the present invention is applied.

FIG. 2 is a block diagram illustrating a configuration of a black generation processing unit and a color correction processing unit.

FIG. 3 is a diagram for explaining the contents of a UCR rate table.

FIG. 4 is a diagram for explaining the contents of a Bk table.

FIG. 5 is a diagram for explaining the contents of a UCR table.

FIG. 6 is a block diagram illustrating a configuration of a black generation processing unit used in an image processing apparatus according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image reading part 2 Image processing part 3 Laser light output part 4 Image formation part 11 Photoelectric conversion part 12 Density conversion part 21 Input processing part 22 Image type discrimination part 23 Black generation processing part 23A Black generation processing part 24 Color correction processing part 25 Output color selection unit 31 MIN data detection unit 32 MAX data detection unit 32A Color reproduction range detection unit 33 Saturation detection unit 33A Saturation detection unit 34 Saturation parameter calculation unit 34A Saturation parameter calculation unit 35 UCR ratio table 36 Multiplier 37 Bk table 41 UCR table 42 C data generator 43 M data generator 44 Y data generator

Continued on the front page F-term (reference) 2C262 AA05 AA24 AA26 AB13 AC04 BA02 BA07 BA13 BA19 BC07 BC09 BC19 EA13 5B057 AA20 CA01 CB01 CE17 5C077 LL19 MP08 PP33 PP35 PP37 PP38 PP39 PP43 PP47 PQ08 PQ23 5C079 HB03 HB03 LA

Claims (3)

[Claims] 1. An image processing apparatus for performing processing on image data that has been color-separated into a plurality of colors for each pixel of an input image, wherein saturation detection is performed to obtain saturation information ci based on the image data of a plurality of colors. Means, a color gamut detection means for obtaining a color gamut r based on the image data of the plurality of colors, and a black color generator for generating a black output value Bk using a saturation parameter c represented by the following equation (A). An image processing apparatus comprising: a generation unit. (Equation 1) 2. The image processing apparatus according to claim 1, further comprising: a maximum value detecting means for detecting a maximum value max of the image data of a plurality of colors; and a minimum value detecting means for detecting a minimum value min of the image data of the plurality of colors. The saturation detecting means obtains the saturation information ci by ci = max-min, and the color gamut detecting means obtains the color gamut by r = max. 2. The image processing device according to 1. 3. The black generating means includes means for obtaining black data K in accordance with the following equation (B), and generates a black output value Bk based on the black data K. 3. The image processing device according to 1 or 2. K = (b−a · c) · min (B) where a and b are positive constants.