JP2002094826A - Image processing unit, image forming unit and method for processing image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To process an accurate color correction at a high speed in image processing in association with a color area compression at a color correction time from input image data to output image data. SOLUTION: A method for processing the image comprises the steps of converting the input image data into halftone image data made of a second color system having a color area range widely set by a color reproducing region of an image output unit when the input image data made of a first color system is converted into the second color system (S1), separating the halftone image data into data out of the color reproducing region of the output unit and data in the color reproducing region (S2), and then compressing the halftone image data to a range of the color reproducing region of the output unit to obtain output image data (S3).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image processing apparatus, an image forming apparatus, and an image processing method for appropriately converting input image data according to a color reproduction area of an image output apparatus.

[0002]

2. Description of the Related Art When input data from a color image input device such as a scanner is displayed or printed out on a color image output device such as a CRT display or an image forming apparatus using an electrophotographic process or an ink jet system,
Normally, the color reproduction area of the color image input device (hereinafter, input color reproduction area) is different from the color reproduction area of the color image output device (hereinafter, output color reproduction area). Have a wide color reproduction range. For this reason, many color image processing methods have been proposed in which the color gamut of the input system is compressed to the color of the output system gamut by color gamut compression to appropriately associate the two color gamut.

For example, in a color conversion apparatus described in Japanese Patent Application Laid-Open No. 9-224162, first, RGB-based input image data is converted into CIEL ^* a ^* b ^* data (CIE: Commission).
Internationale de l'Eclairage (International Commission on Illumination). At this time, input image data of a color outside the virtual color gamut of the output device in which the color gamut of the printer as the output device is enlarged is subjected to hue / color gamut compression processing.
While maintaining the lightness as much as possible, it is converted into output image data of a color corresponding to the position of the outermost edge of the color reproduction space stored in advance.

[0004] Input image data of a color (including a color corresponding to the position of the outermost edge) within the virtually enlarged color reproduction range is converted into color reproduction data of an actual output device in accordance with the saturation. Converted to a range of colors.

[0005]

However, the above-described conventional configuration has the following problems.

For example, the shape of the color reproduction range in the CIEL ^* a ^* b ^* space has a complicated shape as shown in FIG. 11, and the calculation for compressing the color reproduction range becomes very complicated. For this reason, there is a problem that it takes time to perform the arithmetic processing (for example, it is necessary to divide an area by hue and brightness and perform calculation for each area).

[0007] In the processing of the above publication, color coordinate conversion is performed twice (from RGB to RGB) when converting an RGB signal as input image data into a CMY signal as output image data.
L ^* a ^* b ^* , L ^* a ^* b ^* → CMY), and there is a problem that the conversion error at this time becomes large and it is difficult to express an accurate color.

Further, although the lightness L ^* in the CIEL ^* a ^* b ^* space has a defined area, the chromaticity a ^* b ^* does not have a defined area, so that color reproduction in the CIEL ^* a ^* b ^* space is performed. The range can be determined only by the approximate shape, and there is a problem that accurate conversion is difficult.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an image processing apparatus capable of performing high-speed and accurate color correction processing in image processing involving color gamut compression. An object of the present invention is to provide an image forming apparatus and an image processing method.

[0010]

In order to solve the above-mentioned problems, an image processing apparatus according to the present invention converts input-system image data, which is input from an image input unit and has a first color system, to an image output unit. In an image processing apparatus for converting the image data into output system image data having a second color system that can be output by a computer, the input system image data input from the image input unit is set wider than the color reproduction area of the image output unit. Conversion means for converting the image data into intermediate image data having a second color system having the specified color gamut range, and compression means for compressing the intermediate image data into a color reproduction range of the image output means. It is characterized by having.

According to the above arrangement, the input system image data represented by the first color system is used by the second system used in the output system.
When converting to a color system (usually CMY or RGB space), color reproduction is performed as intermediate image data having a color gamut range set wider than the color reproduction region of the image output means in the second color system space. The region is mapped.

Thereafter, by performing compression processing on the intermediate image data, output system image data suitable for the color reproduction area of the image output means is obtained. Here, the second color system space is a cubic space. , The conventional L ^* a ^*
Compared to the case where color gamut compression is performed in the b ^* space, the calculation at the time of performing compression processing is simplified, and high-speed and accurate color correction processing can be performed.

The output image data is not always output directly by the image output means, and is subjected to desired image processing such as black generation / under color removal processing and filter processing. May be output after the operation.

Further, the image processing apparatus further comprises a second
Separating means for separating intermediate image data having a color system into data outside the color reproduction area of the image output means and data in the area. It is possible to adopt a configuration in which data outside the area is compressed to the position of the shortest distance of the outer edge of the color reproduction area of the image output means.

According to the above arrangement, compression processing (data conversion) by the compression means is not performed on the data in the color reproduction area of the image output device separated by the separation means. Also, for data outside the color reproduction area, compression processing is performed so as to be the shortest distance point at the outer edge of the color reproduction area, so that the amount of data conversion by color gamut compression is minimized. Therefore, the intermediate image data of the second color system can be output as a color closest to the input image data of the first color system as a target color, and accurate color reproduction can be achieved. It is possible to do.

The image processing apparatus further comprises a second
After setting a compression boundary slightly inside the outer edge of the color reproduction area of the image output means for the intermediate image data of the color system, the intermediate image data of the second color system is set outside the compression boundary. Separating the data outside the color reproduction area of the image output means from the compression boundary and the outer edge of the color reproduction area. It is possible to adopt a configuration in which compression is performed in a region between them.

According to the above configuration, data outside the compression boundary to be subjected to the compression processing for the color near the outer edge portion where the gradation is likely to be saturated by the compression processing by the compression means is output from the compression boundary to the image output. It is compressed into the area up to the outer edge of the color reproduction area of the means. Therefore, in this area, the gradation of the compressed data is preserved, and it is possible to perform color reproduction while maintaining the gradation.

In the above image processing apparatus, the compression means maintains a component ratio of a plurality of color components for each pixel data of the intermediate image data of the second color system, and controls the color of the image output means. A configuration in which the data is compressed to a reproduction area can be adopted.

According to the above arrangement, the component ratio of each color is maintained before and after the compression by the compression means, and an output which maintains the hue of an original such as a photographic paper having a wide color gamut can be maintained. Becomes Further, color reproduction can be performed without saturating the gradation in the output image.

In the above image processing apparatus, the compression means makes the difference between the maximum value and the minimum value of the plurality of color components substantially constant for each pixel data of the intermediate image data of the second color system. , And compresses the image data into the color reproduction area of the image output means.

According to the above arrangement, the intermediate image data before compression by the compression means and the output system image data after compression are represented by:
The difference between the maximum value and the minimum value of each color component of the image data of the second color system is maintained, and it is possible to perform a color gamut compression process that emphasizes the maintenance of saturation before and after compression.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

FIG. 2 shows a schematic configuration of a digital color copying machine which is an image forming apparatus according to the present embodiment. In the digital color copying machine, as shown in FIG. 2, a color image processing device (image processing means) 1 has a color image input device (image input means) 2 and a color image output device (image output means).
3 as a whole constitutes a digital color copying machine.

The color image processing apparatus 1 has an A /
D conversion unit 10, shading correction unit 11, input gradation correction unit 12, region separation processing unit 13, color correction unit 14, black generation / under color removal unit 15, spatial filter processing unit 16, output gradation correction unit 17, And a tone reproduction processing section 18.

The color image input device 2 is, for example, a CC
D (Charge Coupled Device), and is configured to convert a reflected light image from a document into RGB (R: red, G:
Green / B: blue) analog signals are read by the CCD and input to the color image processing apparatus 1.

The analog signal read by the color image input device 2 is transmitted through the A / D converter 10, the shading corrector 11, and the input gradation corrector 1 in the color image processor 1.
2. The area separation processing unit 13, the color correction unit 14, the black generation / under color removal unit 15, the spatial filter processing unit 16, the output gradation correction unit 17, and the gradation reproduction processing unit 18 are sent in this order.
Is output to the color image output device 3 as a digital color signal.

A / D (analog / digital) converter 10
Is a device for converting an RGB analog signal into a digital signal. The shading correction unit 11 includes an A / D conversion unit 10.
The digital RGB signals sent from the color image input device 2 are subjected to processing for removing various types of distortion generated in the illumination system, the imaging system, and the imaging system.

The input tone correction section 12 outputs an RGB signal (R) from which various distortions have been removed by the shading correction section 11.
At the same time as adjusting the color balance of the GB reflectance signal), a process of converting the signal into a signal such as a density signal which is easy to handle by the image processing system employed in the color image processing apparatus 1 is performed.

The segmentation processing unit 13 converts the RGB signals into
Each pixel in the input image is separated into a character area, a halftone dot area, and a photograph area. The area separation processing unit 13
Based on the result of the separation, an area identification signal indicating which area the pixel belongs to is output to the black generation / under color removal section 15, the spatial filter processing section 16, and the tone reproduction processing section 18, and the input floor is processed. The input signal output from the tone correction processing unit 11 is output as it is to the subsequent color correction unit.

The color correction section 14 removes color turbidity based on the spectral characteristics of CMY (C: cyan, M: magenta, Y: yellow) color materials containing unnecessary absorption components in order to realize faithful color reproduction. The processing is performed. The details of the processing in the color correction unit 14 will be described later.

The black generation / under color removal unit 15 outputs the color-corrected C
Black generation processing for generating a black (K) signal from the three color signals of MY, and under color removal processing for generating a new CMY signal by subtracting the K signal obtained by black generation from the original CMY signal are performed. Through the processing in the black generation / under color removal unit 15, the three CMY color signals are converted into four CMYK color signals.

As an example of the above-described black generation processing, a method of generating black using skeleton black is generally used. In this method, the input / output characteristics of the skeleton curve are represented by y = f
(X), input data is C, M, Y, output data is C ', M', Y ', K', UCR (Under Color R)
If the emoval) rate is γ (0 <γ <1), the black generation / undercolor removal processing is represented by the following equation (1).

[0033]

(Equation 1)

The spatial filter processing unit 16 performs a spatial filter process on the image data of the CMYK signal input from the black generation / under color removal unit 15 by using a digital filter based on the region identification signal, and removes the spatial frequency characteristics. The correction is performed so as to prevent the output image from being blurred or degraded in graininess. Further, similarly to the spatial filter processing unit 16, the tone reproduction processing unit 18 performs a predetermined process on the image data of the CMYK signal based on the region identification signal.

For example, the region separated into the character region by the region separation processing unit 13 is particularly subjected to sharp enhancement processing in the spatial filter processing by the spatial filter processing unit 16 in order to enhance the reproducibility of black characters or color characters. The amount of frequency enhancement is increased. At the same time, the tone reproduction processing section 18 selects binarization or multi-value processing on a high-resolution screen suitable for reproduction of a high frequency.

In addition, the spatial filter processing section 16 performs low-pass filter processing for removing the input halftone dot component on the area separated into the halftone area by the area separation processing section 13. Then, the output tone correction unit 17 performs an output tone correction process of converting a signal such as a density signal into a halftone dot area ratio which is a characteristic value of the color image output device 3. Finally, a tone reproduction process (halftone generation) is performed to separate the image into pixels so as to reproduce the respective tones.

Further, with respect to the area separated into the photographic area by the area separation processing section 13, a binarization or multi-value processing is performed on a screen which emphasizes tone reproducibility.

The image data subjected to each of the above-described processes is
The data is temporarily stored in the storage unit, read out at a predetermined timing, and input to the color image output device 3.

The image output device 3 outputs image data to a recording medium (for example, paper), and includes, for example, a color image forming apparatus using an electrophotographic system or an ink jet system. The image forming method applied here is not particularly limited.

Next, the configuration and operation of the color correction section 14 will be described in detail with reference to FIGS.

As shown in FIG. 3, the color correction section 14
Color data conversion unit (conversion means) 21, color reproduction area setting unit 2
2, a data separation section (separation means) 23 and a color reproduction area compression section (compression means) 24.

The color data conversion unit 21 converts the input image data of the first color system into image data (intermediate image data) of the second color system. The conversion method here is
A commonly used color conversion method such as a method using an LUT (Look Up Table) or a neural network method can be used.

In the configuration of FIG. 3, the first color system is
An RGB color system used for input system image data input from a color image input device 2 such as a scanner.
Is a CMY color system used for print output by the color image output device 3 such as a printer. However, when the color image output device 3 performs display output to a display or the like, the second color system is RGB.
R'G'B 'data color-corrected in consideration of the difference in device characteristics between the input system and the output system using a color system may be used as output system image data.

At this time, as shown in FIG. 3, the first and second color coordinate converters 21 are provided in the color data converter 21.
a, 21b may be provided, and conversion from RGB color coordinates to L ^* a ^* b ^* color coordinates and conversion from L ^* a ^* b ^* color coordinates to CMY color coordinates may be performed by respective color coordinate conversion units. . RG
B-CIEL ^* a ^* b ^* , CIEL ^* a ^* b ^* -CMY
Can be obtained by using a neural network or a masking operation coefficient determining method.

As shown in FIG. 4, the color reproduction area setting section 22 sets the color gamut range of the intermediate image data of the second color system converted by the color data conversion section 21 to [−α, 255 + α]. I do. That is, the color gamut compression processing in the color correction unit 14 takes the intermediate image data of the second color system converted by the color data conversion unit 21 wider than the color reproduction area of the image output device, and Is compressed to the range [0, 255] of the color reproduction area of the image output device, thereby performing color gamut compression in the CMY color space, and obtaining output system image data suitable for the color reproduction region of the image output device. Has become. As described above, the color data conversion unit 21 includes the color reproduction area setting unit 22
The input image data of the first color system is converted into the intermediate image data of the second color system according to the range set in (S).
1: see FIG. 1).

Here, a method for outputting intermediate image data of the second color system converted by the color data conversion unit 21 in a state where the intermediate image data is wider than the color reproduction area of the image output device will be described.

As an example, considering the case where RGB data of the first color system is converted to CMY data of the second color system, the simplest method is a conversion method using a linear matrix. A large number of color patches (CMY) output from the image output device are scanned to obtain their read data (RGB). From the correspondence, (c, m, y) = MTX × (r, g, b) The following matrix MTX may be obtained.

For example, the brightest yellow ((c, m, y) = (0, 0, 25) that can be output by the image output device.
5)), the scanned data is (r,
g, b) = (200,200,20), then, in the conventional conversion method, (0,0,255) = MTX × (200,200,2)
0) is set in the matrix MTX.

On the other hand, in the present invention, the color when scanning a more vivid yellow is (r, g, b) = (23)
0, 230, 10), the data of the second color system corresponding to this is (c, m, y) = (− 5, −
5, 260) outside the defined range (outside the range that can be output by the image output device). In this way, some provisional value data are set, and the color patch data and the provisional data are combined to form a matrix MTX2 such that (c, m, y) = MTX2 × (r, g, b). Ask. When the RGB data as the first color system is converted into the CMY data as the second color system by using the matrix obtained in this way, if the conversion is performed by a linear matrix, C as output data can be obtained.
A value outside the defined range for MY data can be output.

The color gamut of the intermediate image data is uniformly extended in both the positive and negative directions around the value of [128], which is the center value, with respect to the range of [0, 255] to be output. It is preferred that

In FIG. 4, the color reproduction range of the intermediate image data and the output system image data is actually CMY.
Is a three-dimensional cubic space represented by, but FIG. 4 shows only the color reproduction range on the CM plane for the sake of simplicity. Further, in the figure, the range in which the output image data is expanded is set to the same value α in the C-axis and M-axis directions, but this value does not need to be set to the same value in the C-axis, M-axis, and Y-axis directions. The range of α is preferably about 10 to 50.

The data separation section 23 converts the intermediate image data of the second color system into a predetermined range, for example, data outside the color reproduction area of the color image output device 3 and data inside the color reproduction area (at the position of the outermost edge). (Including corresponding image data) (S2). How to separate the intermediate image data of the second color system differs depending on the compression method. A method of compressing the second color system intermediate image data will be described later.

The color reproduction area compression unit 24 compresses the intermediate image data of the second color system so as to fall within the color reproduction area of the color image output device to obtain output system image data (S).
3).

Next, a specific example of the color gamut compression method (compression mode) in the color correction section 14 will be described.

[Example 1: Absolute colorimetric method] In the color gamut compression method in Example 1, the intermediate image data of the second color system converted by the color data conversion unit 21 is compressed into the color reproduction area of the image output device. In doing so, as shown in FIG. 5, the intermediate image data of the second color system is converted into data outside the color reproduction area of the image output device and data inside the color reproduction area (image data corresponding to the position of the outermost edge). Data). Then, compression processing is performed on data outside the color reproduction area of the image output device so as to be a point at the shortest distance at the outer edge of the color reproduction area.

That is, in the method of the first embodiment, in each of the CMY data in the intermediate image data of the second color system, data having a value of “0” or less is converted to a value of “0” by the color gamut compression. Converted to data. Also, "255"
The data having the above values is “25” by the color gamut compression.
5 ". An arithmetic expression in the conversion at this time is represented by the following expression (2).
In the above equation (2), x indicates a data value in each of CMY of the intermediate image data output from the color data conversion unit 21, and f (x) indicates output system image data after color gamut compression is performed. Shows the data value at.

[0057]

(Equation 2)

As described above, in the color gamut compression method according to the first embodiment, data in the color gamut of the image output device is not converted by color gamut compression. Also, for data outside the color reproduction area, compression processing is performed so as to be the shortest distance point at the outer edge of the color reproduction area.
The amount of data conversion by color gamut compression is minimized. For this reason,
The output image data from the color correction unit 14 is
Can be output as the CMY value closest to the color (target color) input to the image processing apparatus 1, so that accurate color reproduction can be performed.

However, in the method of the first embodiment, since all data outside the color reproduction area of the image output device is compressed to the position of the outermost edge of the color reproduction area, the color near the outer edge to be compressed is The gradation is reduced.

[Example 2: relative colorimetric method] In the method of Example 1 described above, although color reproduction accuracy can be obtained,
There is a problem that the gradation near the outer edge to be compressed is reduced. The color gamut compression method according to the second embodiment aims to suppress the lowering of the gradation, and suppresses the lowering of the gradation by compressing the data outside the color reproduction area into a narrow area at the outer edge. .

More specifically, as shown in FIG.
Within the color reproduction area of the image output device, the width β
A compression area (about 5 to 25) is set. The innermost boundary of the compression area is defined as a compression boundary, and the data separation unit 23 separates the intermediate image data of the second color system into data outside the compression boundary and data inside the compression boundary (including the compression boundary). I do. Then, the color reproduction area compression section 24 compresses the data outside the compression boundary so that the data falls within the compression area.

That is, in this compression processing, (the distance to the compression boundary in the data after compression) becomes (the distance to the compression boundary in the data before compression) and (the compression ratio: β /
(Α + β)). An arithmetic expression in the conversion at this time is represented by the following expression (3).

[0063]

(Equation 3)

For example, when α = 30 and β = 5, in the above method, the minimum value equal to or less than “0”, for example, “−30”
Is converted to “0”, and data having a maximum value of “255” or more, for example, data having a value of “285” is converted to “255”.

As described above, according to the color gamut compression method shown in the second embodiment, data outside the compression boundary to be subjected to compression processing is applied to the color near the outer edge portion where gradation saturation is likely to occur due to the color gamut compression. Is compressed in a region from the compression boundary to the outer edge of the color reproduction region of the image output device. For this reason, the gradation of the compressed data is preserved in this area, and it is possible to perform color reproduction while maintaining the gradation more than in Example 1.

[Example 3: Perceptual method] In the color gamut compression methods of Examples 1 and 2 above, processing emphasizing reproducibility was possible. However, in Example 3, compression is performed while maintaining hue. Is exemplified. In the CMY (or RGB) space, the component ratio of each color represents a hue. Therefore, in the color gamut compression method of the third embodiment, compression is performed so that the component ratio of each color is maintained before and after compression. An arithmetic expression in the conversion at this time is represented by the following expression (4). In the compression method according to the third embodiment, since the calculation using the same equation (4) is performed for all the pixels, the separation process by the data separation unit 23 in the color correction unit 14 is omitted.

[0067]

(Equation 4)

In the color gamut compression method according to the third embodiment, FIG.
When (a) is the pixel data of the intermediate image data before compression and FIG. 7 (b) is the pixel data of the output image data after compression, the component ratio of each color is maintained before and after compression. in _{order, (x C + α) :(} x M + α) :( x Y + α) = (x C ') :( x M') :( x Y ') must relationship is established, the equation This relationship can be satisfied by the calculation shown in (4).

As described above, according to the color gamut compression method of the third embodiment, the component ratio of each color is maintained before and after compression, and the hue is maintained even in an original such as a photographic paper photograph having a wide color gamut. Output is possible. Further, color reproduction can be performed without saturating the gradation in the output image.

[Example 4: Saturation method] This example 4 proposes a color gamut compression method that emphasizes the maintenance of saturation before and after compression. The saturation in CMY (or RGB) space is C,
The difference between the maximum and minimum values of M and Y, that is, max (c,
m, y) -min (c, m, y), so that if this value is maintained and compressed, the saturation can be maintained before and after compression.

In the color gamut compression method of the fourth embodiment, first, the second
In the intermediate image data of the color system, the value exceeding the maximum value outside the color reproduction area of the image output device is defined as ε, and the minimum value is defined as φ, and the values of ε and φ are expressed by the following equations (5) and (6). ).

[0072]

(Equation 5)

[0073]

(Equation 6)

Then, based on the values of ε and φ, the data value after compression is obtained by one of the following three operations. That is, in the compression method of the fourth embodiment, the values of ε and φ are calculated in the data separation unit 3, and pixel data satisfying ε> 0 and φ> 0, ε> 0 and φ
= 0, ε = 0 and φ> 0, and ε = 0 and φ = 0. In the following description, a case where C ≦ M ≦ Y will be described as an example.

First, when ε> 0 and φ> 0, FIG.
When (a) is data before compression and FIG. 8 (b) is data after compression, since ε> 0, the data value of Y having the maximum value is 255 + ε and has the minimum value. The data value of C is -φ. Therefore, the saturation in the data before compression is 255 + ε − (− φ) = 255 + ε
+ Φ. Since this value exceeds the maximum width 255 of the color reproduction area of the image output device, when ε> 0 and φ> 0, the maximum value of C, M, and Y before and after the compression processing is performed. And the minimum, i.e., the saturation, cannot be completely preserved.

Therefore, in this case, in order to maintain the saturation before and after compression as much as possible, the data value before compression is 25
For the Y data exceeding 5, the value of ε is subtracted to convert the data value Y ′ after compression to 255, and for the C data whose data value before compression is smaller than 0, the value of φ is added. Thus, the data value C ′ after the compression is converted to be 0. For the data of M, the value of φ is added and the value of ε is subtracted to calculate the data value M ′ after compression.

That is, the arithmetic expression in the compression processing when ε> 0 and φ> 0 is represented by the following expression (7). If the value of M + φ−ε exceeds 255 or becomes smaller than 0, the value is outside the color reproduction range of the image output device. In this case, the value of M ′ is 25.
Converted to 5 or 0.

[0078]

(Equation 7)

Next, when ε> 0 and φ = 0, FIG.
When (a) is data before compression and FIG. 9 (b) is data after compression, since ε> 0, the data value of Y having the maximum value is 255 + ε, and the data value of Y is Is a value outside the color reproduction region of the image output device, and is converted so that the data value Y ′ after compression becomes 255 by subtracting the value of ε.

At this time, the data of C having the minimum value is
In order to maintain the saturation before and after the compression, the value of the compressed data value C ′ is subtracted by subtracting the value of ε similarly to the Y data.
Is required. It is also assumed that the data value M ′ after compression is obtained by similarly subtracting the value of ε from the data of M.

That is, the arithmetic expression in the compression processing when ε> 0 and φ = 0 is expressed by the following expression (8). However, in this case, if the value of C−ε or M−ε becomes smaller than 0, the value becomes outside the color reproduction area of the image output device. In this case, C ′ or M ′
Is converted to 0.

[0082]

(Equation 8)

Next, when ε = 0 and φ> 0, FIG.
When 0 (a) is data before compression and FIG. 10 (b) is data after compression, φ> 0, so that the data value of C having the minimum value is −φ, Since the data value is a value outside the color reproduction area of the image output device, the data value is converted so that the compressed data value C ′ becomes 0 by adding the value of φ.

At this time, the data of Y having the maximum value is
In order to maintain the saturation before and after the compression, the value of the compressed Y ′ is added by adding the value of φ in the same manner as the C data.
Is required. It is also assumed that the data value M ′ after compression is obtained by similarly adding the value of φ to the data of M.

That is, the arithmetic expression in the compression processing when ε = 0 and φ> 0 is given by the following expression (9). However, in this case, if the value of Y + φ or M + φ exceeds 255, it becomes a value outside the color reproduction area of the image output device. In this case, the value of Y ′ or M ′ is converted to 255. Is done.

[0086]

(Equation 9)

Further, when ε = 0 and φ = 0, since all the data values of CMY in the data before compression exist in the color reproduction area of the image output device, data value conversion is required. Instead, the saturation before and after the compression processing is naturally maintained.

As described above, in the color gamut compression method according to the fourth embodiment, the difference between the maximum value and the minimum value of C, M, and Y before and after compression is maintained as much as possible. This makes it possible to perform color gamut compression processing that emphasizes the maintenance of saturation before and after compression.

The selection of each of the compression modes described in the above Examples 1 to 4 is performed by using the operation panel 4 (constituted by a display unit composed of a liquid crystal display, setting buttons, etc .: see FIG. 2) provided in the image forming apparatus. The user can arbitrarily input and instruct. At this time, a brief description of the compression mode (compression method) is added to the display unit, or not what the compression mode itself is, but what kind of image is obtained by each compression mode is displayed to the user. It is preferable for the user to select a desired mode because it is easy for the user to understand.

[0090]

As described above, the image processing apparatus of the present invention converts the input system image data input from the image input means into a color gamut set wider than the color reproduction area of the image output means. And a compression unit for compressing the intermediate image data into a range of a color reproduction area of the image output unit.

Therefore, the input-system image data represented by the first color system is converted into an intermediate image having a color gamut wider than the color reproduction region of the image output means in the second color system space. Map the color reproduction area as image data,
Then, by performing the compression process on the intermediate image data, the calculation when performing the compression process is simplified as compared with the case of performing the color gamut compression in the conventional L ^* a ^* b ^* space, and high-speed and accurate color There is an effect that correction processing can be performed.

The image processing apparatus further includes a second
Separating means for separating intermediate image data having a color system into data outside the color reproduction area of the image output means and data in the area. It is possible to adopt a configuration in which data outside the area is compressed to the position of the shortest distance of the outer edge of the color reproduction area of the image output means.

Therefore, the data outside the color reproduction area to be subjected to the compression processing by the compression means is subjected to the compression processing so as to be the shortest point at the outer edge of the color reproduction area. Since the amount of data conversion by compression is minimized, and the intermediate image data can be output as the color closest to the input system image data of the first color system, accurate color reproduction can be performed. It works.

The image processing apparatus further includes a second
After setting a compression boundary slightly inside the outer edge of the color reproduction area of the image output means for the intermediate image data of the color system, the intermediate image data of the second color system is set outside the compression boundary. Separating the data outside the color reproduction area of the image output means from the compression boundary and the outer edge of the color reproduction area. It is possible to adopt a configuration in which compression is performed in a region between them.

Therefore, the data outside the compression boundary to be subjected to the compression processing is compressed in the area from the compression boundary to the outer edge of the color reproduction area of the image output means. The effect is that gradation is preserved, and color reproduction with more maintained gradation can be performed.

In the image processing apparatus, the compression means maintains the component ratio of a plurality of color components for each pixel data of the intermediate image data of the second color system and maintains the color ratio of the image output means. A configuration in which the data is compressed to a reproduction area can be adopted.

Therefore, the component ratio of each color is maintained before and after compression by the compression means, so that an output such as a photographic paper having a wide color gamut can be output while maintaining its hue. It works.

In the above image processing apparatus, the compression means makes the difference between the maximum value and the minimum value of the plurality of color components substantially constant for each pixel data of the intermediate image data of the second color system. , And compresses the image data into the color reproduction area of the image output means.

Therefore, the difference between the maximum value and the minimum value of each color component of the second color system image data is maintained between the intermediate image data before compression by the compression means and the output system image data after compression. In addition, there is an effect that a color gamut compression process can be performed with emphasis on maintaining saturation before and after compression.

[Brief description of the drawings]

FIG. 1 illustrates one embodiment of the present invention, and is a flowchart illustrating a schematic operation of image processing.

FIG. 2 is a block diagram illustrating a configuration of a digital color copying machine including the image processing apparatus of the present invention.

FIG. 3 is a block diagram illustrating a configuration of a color correction unit provided in the image processing apparatus.

FIG. 4 is an explanatory diagram showing a state in which a color reproduction area before and after compression in a CMY color system is mapped on a CM plane.

FIG. 5 is an explanatory diagram showing a compression method according to a first example of a color reproduction area compression method used in the image processing apparatus.

FIG. 6 is an explanatory diagram showing a compression method according to a second example of a color reproduction area compression method used in the image processing apparatus.

FIG. 7 is an explanatory diagram showing a compression method according to a third example of a color reproduction area compression method used in the image processing apparatus;
(A) shows image data before compression, and (b) shows image data after compression.

8A and 8B are explanatory diagrams showing a part of a compression method according to a fourth example of a color reproduction area compression method used in the image processing apparatus, wherein FIG. 8A shows image data before compression, and FIG. This shows the compressed image data.

9A and 9B are explanatory diagrams showing a part of a compression method according to a fourth example of a color reproduction area compression method used in the image processing apparatus, wherein FIG. 9A shows image data before compression, and FIG. This shows the compressed image data.

10A and 10B are explanatory diagrams illustrating a part of a compression method according to a fourth example of a color reproduction area compression method used in the image processing apparatus, wherein FIG. 10A illustrates image data before compression, and FIG. This shows the compressed image data.

FIG. 11 is an explanatory diagram showing a state in which a color reproduction area in an L ^* a ^* b ^* space is mapped on an L ^* b ^* plane.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 color image processing device (image processing means) 2 color image input device (image input means) 3 color image output device (image output means) 21 color data conversion section (conversion means) 23 data separation section (separation means) 24 color reproduction Area compression unit (compression means)

Continued on the front page F-term (reference) 2C262 AA24 AA26 AB11 BA01 BC19 CA10 EA08 5B057 AA11 CA01 CA08 CA12 CA16 CB01 CB08 CB12 CB16 CC01 CE18 DB02 DB06 DB09 DC25 5C077 LL19 MP08 PP27 PP28 PP32 PP33 PP37 PP47 PP52 HB10B11C LA26 LB02 NA03 NA11 NA29

Claims (7)

[Claims] 1. Image processing for converting input system image data input from an image input unit and comprising a first color system into output system image data comprising a second color system which can be output by an image output unit. In the apparatus, the input-system image data input from the image input unit is
Conversion means for converting the intermediate image data into intermediate image data having a second color system having a color gamut set wider than the color reproduction area of the image output means; An image processing apparatus comprising: compression means for compressing an area. 2. The image processing apparatus according to claim 1, further comprising: separating means for separating the intermediate image data of the second color system into data outside the color reproduction area of the image output means and data in the area. 2. The data compression method according to claim 1, wherein the data outside the color reproduction area of the image output means is compressed to a position of the shortest distance of the outer edge of the color reproduction area of the image output means.
An image processing apparatus according to claim 1. 3. A compression boundary is set slightly inside the outer edge of the color reproduction area of the image output means for the intermediate image data of the second color system. Separating the intermediate image data into data outside the compression boundary and data inside the compression boundary, wherein the compression unit converts data outside the color reproduction region of the image output unit into the compression boundary. The image processing apparatus according to claim 1, wherein the image is compressed to an area between the outer edge of the color reproduction area. 4. The image processing apparatus according to claim 1, wherein said compression means maintains a component ratio of a plurality of color components for each pixel data of the intermediate image data of the second color system and compresses the pixel data into a color reproduction area of the image output means. The image processing apparatus according to claim 1, wherein: 5. The image output apparatus according to claim 1, wherein the compression means maintains the difference between the maximum value and the minimum value of the plurality of color components substantially constant for each pixel data of the intermediate image data of the second color system. 2. The image processing apparatus according to claim 1, wherein the image is compressed to a color reproduction area of the means. 6. An image input means for generating input image data of a first color system, and an output image of a second color system based on the input image data generated by the image input means. 6. An image processing unit for converting data into data, and an image output unit for performing an output process using the output system image data converted by the image processing unit. An image forming apparatus, comprising: the image processing apparatus according to any one of the above. 7. An image processing method for converting input-system image data having a first color system into output-system image data having a second color system. When the image data is converted into the second color system, the image data is temporarily converted into intermediate image data having the second color system having a color gamut wider than the color reproduction region of the image output unit. An image processing method for obtaining output system image data by compressing the intermediate image data to a range of a color reproduction area of the image output means.