JPH10198793A - Image processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processor that can perform arbitrary color control, that is reduced in memory capacity and cost. SOLUTION: The image inputted from an image input part 1 is sent through an input gradation correcting part 2 and a 1st chrominance signal converting part 3 to a color control matrix part 6 as the signal of color space L*a*b*. The lightness, saturation, and hue are controlled over all the color space L*a*b* at the color control matrix part 6 and the image is sent to a 2nd chrominance signal converting part 7. At the 2nd chrominance signal converting part 7, local control disabled for matrix transformation is applied to L*a*b* signal and the signal is converted output to a YMCK signal to be applied to an image output part 16. Through two stages of color control, arbitrary color control is enabled.

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 and processing in an image processing apparatus such as a digital copying machine, a scanner, a printer, a facsimile, a CRT, and image-related software such as an image system and a color management system. It is about the method.

[0002]

2. Description of the Related Art Conventionally, a color adjustment method in a color copying machine has been disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 5-14699. Adjustment and gamma adjustment are known. This adjustment method is to convert the RGB signal to the L ^* a ^* b ^* signal is a standard signal, L ^* a ^*
against b ^* signals, performs matrix calculation to convert the predetermined adjustment L ^* a ^* b ^* signal. After that, it is converted into a YMC signal, which is an output device signal, and is further subjected to under color removal processing (U
CR), a YMCK signal is generated, and an image is output from the output device.

In a color copying machine, an image processing method for performing color conversion is called a masking method.
The above-described linear matrix operation method and higher-order nonlinear matrix operation method are known. Further, as a method for improving the color conversion accuracy, there is a color conversion method using a multidimensional direct lookup table. In the color conversion method using the direct lookup table, an input color space is divided by a grid, and data (grid point data) of an output color space corresponding to the grid points is prepared. The output signal is determined by an interpolation operation using grid point data near the input signal.

As a color adjustment method in such a direct look-up table, signal compression (gamut compression) for matching a color reproduction range of an input device and an output device is known. Generally, an L ^* a ^* b ^* signal is used. And is intended for color matching rather than color adjustment.

[0005] Further, a "color value converter" described in JP-A-6-296231 and JP-A-6-268 are disclosed.
In a "color correction device" described in Japanese Patent Application Publication No. 854, an affine transformation or a matrix transformation circuit is provided in a stage preceding the direct lookup table. In these devices, the direct look-up table performs conversion for the entire color space. Particularly, in the device described in the latter document, higher-order nonlinear correction is realized. In such a configuration, the affine transformation and the matrix transformation circuit perform the transformation for improving the transformation accuracy in the next direct look-up table, and do not perform the color adjustment according to the original mode or the user's preference. .

When color adjustment is performed in these apparatuses, the main means for color conversion is a direct look-up table, so that the direct look-up table is changed. In order to perform color adjustment using a direct look-up table, parameters created in advance are resident in a memory, and parameters selected by a user's designation or the like are set in the direct look-up table. At that time, in order to realize all combinations of adjustment items with the parameters of the direct look-up table, a huge number of combinations are required.
There is a problem that a huge amount of memory is required, and the system size and the price increase.

[0007] For the purpose of color adjustment, for example, there is an "image recording apparatus" described in JP-A-6-299664. In this apparatus, an adjustment one-dimensional lookup table and a conversion means using a linear matrix are provided at a stage preceding the direct lookup table.
The RGB signal input by the dimensional lookup table is converted to N
It is converted to a YIQ signal of the TSC standard, and brightness, gradation and hue adjustment are calculated by linear matrix processing, and Y'I '
The Q 'signal is obtained and converted to an output signal by a direct lookup table. Furthermore, color adjustment is made possible by linear matrix processing.

However, in this document, since color adjustment is performed by linear matrix processing, adjustment can be made only for the entire color space. With a simple matrix operation, it is impossible to adjust any color and color area. Such a region needs to be adjusted in a direct look-up table that performs conversion to an output signal, but such adjustment cannot be made in this document.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an image processing apparatus capable of performing arbitrary color adjustment and reducing memory capacity and cost. Is what you do.

[0010]

According to a first aspect of the present invention, in an image processing apparatus, a first color for adjusting an m-dimensional color signal corresponding to a color of a first color system in a full color space. A signal processing means for converting an m-dimensional color signal corresponding to the color of the first color system into an n-dimensional color signal corresponding to the color of the second color system using a lookup table with interpolation; A second color signal processing means for adjusting a local color space is provided.

According to a second aspect of the present invention, in the image processing apparatus according to the first aspect, the first color signal processing means performs color adjustment by a linear matrix operation method.

According to a third aspect of the present invention, in the image processing apparatus according to the first or second aspect, the first color signal processing means includes a lightness, a saturation, a hue, a gray balance, The gamma characteristic is adjusted, and the second color signal processing means adjusts lightness, saturation, hue, gray balance, and gamma characteristic in a local color space.

[0013]

FIG. 1 is a block diagram showing an example of an image forming apparatus including an image processing apparatus according to an embodiment of the present invention. In the figure, 1 is an image input section, 2 is an input tone correction section, 3 is a first color signal conversion section, 4 is a character / photograph / color / black separation section, 5 is a document mode decoder, and 6 is a color adjustment matrix section. , 7 are second color signal converters, 8, 11 are selectors,
Reference numerals 9 and 10 denote FIFOs, 12 denotes a main scanning reduction / enlargement unit, 13 denotes a spatial filter processing unit, 14 denotes an output gradation correction unit, 15 denotes an output screen switching unit, and 16 denotes an image output unit.

The image input unit 1 decomposes an image on a document into 8-bit R, G, and B color signals at a predetermined pixel density, and sends the color signals to the input tone correction unit 2 in pixel order. Input tone correction unit 2
Performs gradation conversion depending on the image input unit 1 and sends it to the first color signal conversion unit 3. In the first color signal converter 3,
The RGB color signals L ^*, a ^*, b ^* is converted into the 8-bit color signals, and sends the text / photo-color black separation section 4 and the color adjustment matrix section 6.

The character / photo / color / black separation section 4 is L ^* a ^* b
^* Based on the color signal, it is determined whether or not the input pixel is a character, and if it is a character, whether it is an achromatic color or a chromatic color. The determination result is passed to the document mode decoder 5. The document mode decoder 5 converts the document mode signal from the identification result by the character / photograph / color / black separation unit 4 and the document mode designation TAG information set by the user into the second color signal conversion unit 7, the selectors 8, 11, Spatial filter processing unit 13, output gradation correction unit 1
4. Output to the output screen switching unit 15. Each unit receiving the document mode signal processes each unit with parameters according to the document mode.

In the color adjustment matrix section 6, all L ^* a ^* b ^*
The lightness, saturation, and hue are converted over the color space and sent to the second color signal converter 7. In the second color signal converter 7, L
^{The *} a ^* b ^* signal is locally adjusted, converted into a YMCK signal to be supplied to the image output unit 16, and sent to the selector 8. Here, two types of Y / M / C / K are performed by performing color adjustment and color conversion processing corresponding to two types of original modes.
The signals are converted into signals S1 and S2 and sent to the selector 8. For example, the YMCK signal S1 can be an output value for a photograph that requires high color conversion accuracy, and the YMCK signal S2 can be an output value in a character mode or a map mode that requires only low color conversion accuracy.

The selector 8 selects Y
Select one of the MCK signals S1 and S2 and
Output to On the other hand, the L ^* signal output from the first color signal converter 3 is input to the FIFO 10 for black characters. One of the outputs of the FIFO 9 and the FIFO 10 and the '0' signal is selected by the selector 11 according to the document mode signal, and sent to the main scanning reduction / enlargement unit 12.

The main scanning reduction / enlargement unit 12 enlarges or reduces in the main scanning direction according to a set enlargement ratio or reduction ratio. In addition, enlargement / reduction in the sub-scanning direction
This can be performed by changing the scanning speed of the image input device 1 in the sub-scanning direction. Thereafter, the spatial filter processing unit 13 performs processing such as sharpening processing and noise removal, the output correction unit 14 performs gradation conversion according to the image output unit 16, and the output screen switching unit 15 follows the original mode signal. The output screen is selected and used to form an output image, and an image is formed by the image output unit 16.

FIG. 2 is a block diagram showing an example of the second color signal converter. In the figure, reference numeral 21 denotes a three-dimensional lookup table color conversion LSI. The second color signal conversion unit 7 can use a three-dimensional lookup table color conversion LSI 21 with an interpolation function, for example, as shown in FIG. Note that the direct lookup table color conversion L
The role of each input signal line of SI21 is shown in FIG.
As shown in FIG.

Direct Lookup Table Color Conversion L
SI21 is a direct lookup table color conversion L
It consists of three parts: setting of grid point data (color conversion parameters) in a storage unit inside the SI 21, operation setting at the time of color conversion, and color conversion. The setting of the grid point data (color conversion parameter) in the storage section inside the direct look-up table color conversion LSI 21 is performed by invalidating the register setting by a reset signal and by the write enable signal in the storage section inside the direct lookup table color conversion LSI. Then, the grid point data is written to the storage unit inside the three-dimensional look-up table color conversion LSI 21 according to the timing of the clock signal. By providing point data as a grid point data signal, desired color conversion parameters can be set. In the case of an image recording apparatus that prints for each plate of the output color separated into each of C, M, Y, and K, this setting is set to the next output color in the inter-image (change between colors and colors). You can do it again. The operation setting at the time of color conversion is performed by a register signal and a TAG ′ signal which is a document mode signal received from the document mode decoder 5. At the time of color conversion, L
By inputting each signal of ^* , a ^* , and b ^* , interpolation processing is performed using the previously set grid point data, and the color conversion result is output as an output signal.

The determination of the color conversion parameters of the direct look-up table in the second color signal converter 7 and the local color adjustment will be described. The color conversion parameters of the direct look-up table are as shown in FIG.
The dimension lookup table is set by giving K / Y / M / C grid point data stored in the storage unit inside the color conversion LSI 21. Here, first, in order to faithfully reproduce the color data of each of L ^* , a ^* , and b ^* corresponding to the grid point as the output result of the image output device 16, the setting is performed by using the following output result prediction method. I do.

The output result predicting method means that, for an arbitrary combination of K, C, M, and Y values of a certain output device, an output color (expressed by a value in an L ^* a ^* b ^* color space) is used. It is to be able to correspond. Conversely, the values of K, C, M, and Y can be associated with the colors output from the output device. By using such an output result prediction method, the values of K, C, M, and Y corresponding to the L ^* a ^* b ^* colors corresponding to the grid points can be obtained, and the values can be stored as grid point data. For example, a color conversion parameter of a direct lookup table can be set. However, in general, the input L ^* a ^*
Since the range of the b ^* color space is larger than the range of colors reproducible by the output device, it is necessary to set in combination with the above-described color reproduction space mapping technique when applying the output result prediction method. Although several types of color reproduction space mapping techniques have been conventionally known, they are not specifically defined here.

FIG. 3 is an explanatory diagram of an example of an output result prediction method. In order to determine the color conversion parameters of the direct look-up table, first, in order to correct the gradation of the image output unit 16, the coefficient of the output gradation correction unit 14 is determined as shown in FIG. In determining the coefficients, Y, M, C,
The K single-color patches are recorded by the image output unit 16, and the patch images are measured to obtain colorimetric data (L ^* a ^* b ^* ) and correspond to the output data (coverage signal YMCK). As a result, a one-dimensional lookup table for gradation correction can be determined so as to cancel the adverse effects (bad gray balance, non-linearity of gradation, etc.) due to device characteristics of the image output unit 16. This may be set in the output gradation correction unit 14.

Next, as shown in FIG. 3B, a plurality of color combinations (C, M, Y) that can be output are prepared, and actually output from the image output device 16 through the created one-dimensional lookup table. To make a sample. The color of the created sample is measured, and the color is measured, for example, (L ^* , a ^* ,
b ^* ) data and the corresponding (C, M, Y) data, (L ^* , a ^* , b ^* ) to (C, M, Y) using a high-order matrix approximation such as 3 × 10. M, Y) can be approximated. In this case, the calculation of K and the under color removal (UCR) were approximated (C,
M, Y), and plates for four colors can be created.

Further, using (C, M, Y, K) and (L ^* , a
^* , B ^* ) is approximated and directly expressed as (L ^* , a ^* , b)
^* ), A prediction method capable of calculating (C, M, Y, K) may be used. Various prediction methods are known,
An appropriate technique may be used in consideration of the required prediction accuracy and the like. From the predicted relationship from (L ^* , a ^* , b ^* ) to (C, M, Y), the color conversion parameter of the direct lookup table can be determined.

As described above, the parameters of the direct lookup table in the second color signal conversion unit 7 are determined by using the output prediction method, the color reproduction space mapping technology, and the like.

Next, the color adjustment will be described. The overall adjustment is performed by the color adjustment matrix unit 6. The color adjustment matrix unit 6 adjusts lightness, saturation, and hue as a whole, and L ^* a
Convert ^* b ^* to L ^* 'a ^* ' b ^* '. FIG. 4 is an explanatory diagram of a color adjustment method in the color adjustment matrix section. Generally, color conversion can be performed by a linear matrix operation shown in FIG. At this time, as shown in FIG. 4B, the conversion matrix can be decomposed into a product of three conversion matrices of lightness, saturation, and hue. In this conversion matrix, the value of D may be changed when adjusting the lightness, the value of K may be changed when adjusting the saturation, and the angle θ may be changed when adjusting the hue. do it.

For example, as the lightness adjustment value D, 0.8
x, 0.9x, 1.0x, 1.1x, 1.2x, 1.3
6 levels of x (where x is standard lightness), hue angle θ
-5 degrees of -20 degrees, -10 degrees, 0 degrees, 10 degrees, and 20 degrees, and the saturation value K is 0.8 times, 0.9 times,
Five levels of 1.0 times, 1.15 times, and 1.3 times can be selectively used. There are as many conversion matrices as there are combinations, and the user can select from 150 types of matrix parameters.
Of course, each value may be set arbitrarily by the user.

Next, local color adjustment will be described.
Local color adjustment is performed by the second color signal converter 7. The color conversion parameters once determined as described above are adjusted according to the purpose (hue, saturation, density). For example, in order to prevent fogging in a highlighted portion, data having the highest brightness and the lowest saturation (L ^* , a ^* , b ^* = 9)
(5, 0, 0, etc.) can be set to 0 so that ink does not get on the recording paper. Further, in order to adjust the gray balance, the YMC data of the gray axis or the gray axis and lattice points near the gray axis can be equalized. Or,
Colors that cannot be reproduced by the image output unit 16, that is, colors outside the color reproduction range, can be adjusted by hue, saturation, and density. At this time, it is also possible to individually adjust each grid point, or to adjust using grids.

In this way, any local adjustment (change of hue, saturation, density) intended for the purpose of image quality can be performed. The adjustment instruction in this case can be given in various forms, such as the user giving an instruction using a user interface such as a control panel, or the maintenance staff giving the instruction in the same manner as the maintenance inspection operation according to the user's request.

As described above, by combining the overall adjustment by the color conversion matrix unit 6 and the local adjustment by the second color signal conversion unit 7, the color of the output document is brought closer to the color that the user really intends by the color adjustment. be able to.

FIG. 5 is a block diagram showing an example of another system to which an embodiment of the image processing apparatus of the present invention is applied. In the figure, 31 is a photo CD, 32 is a scanner, 33
Is a host computer, and 34 and 35 are color printers. The present invention can be applied not only to the color conversion system of a digital color copying machine as shown in FIG. 1 but also to a color conversion unit of an image processing system via a network as shown in FIG. For example, the host computer 33 has various functions for performing color conversion, for example, a portion excluding the image input unit 1 and the image output unit 15 in FIG. To perform color conversion and output to the color printers 34 and 35. In the host computer 33, the color adjustment for the entire color space and the local color adjustment set according to the instruction from the user or the like are performed on the input image, so that the output image of the color tone intended by the user can be obtained. it can.

[0033]

As is apparent from the above description, according to the present invention, since the color adjustment is performed by the color adjustment over the entire color space and the local color adjustment, the color is adjusted to an arbitrary color tone desired by the user. be able to. Further, by performing such color adjustment by combining a matrix operation and a direct look-up table, there is an effect that even if the number of adjustments is large, the memory capacity and cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of an image forming apparatus including an embodiment of an image processing apparatus according to the present invention.

FIG. 2 is a configuration diagram illustrating an example of a second color signal conversion unit.

FIG. 3 is an explanatory diagram of an example of an output result prediction method.

FIG. 4 is an explanatory diagram of a color adjustment method in a color adjustment matrix unit.

FIG. 5 is a block diagram illustrating an example of another system to which an embodiment of the image processing apparatus according to the present invention is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image input part, 2 ... Input gradation correction part, 3 ... First color signal conversion part, 4 ... Character / photograph / color black separation part, 5 ... Original mode decoder, 6 ... Color adjustment matrix part, 7 ... Second color signal converters, 8, 11,... Selectors, 9, 10,.
12: main scanning reduction / enlargement unit, 13: spatial filter processing unit,
14: output gradation correction unit, 15: output screen switching unit, 16: image output unit, 21: three-dimensional lookup table color conversion LSI, 31: photo CD, 32: scanner, 33: host computer, 34, 35 ... Color printer.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H04N 9/67 H04N 1/40 D 1/46 Z (72) Inventor Hitoshi Kogachi 430 Nakai-cho, Nakaicho, Ashigara-gun, Kanagawa Prefecture Green Tech Naka Fuji Xerox (72) Inventor Atsushi Kitagawara 2274 Hongo, Ebina-shi, Kanagawa Prefecture Fuji Xerox Co., Ltd.

Claims (3)

[Claims] 1. A first color signal processing means for adjusting an m-dimensional color signal corresponding to a color of a first color system for an entire color space, and an m-dimensional signal corresponding to a color of the first color system. Is converted into an n-dimensional color signal corresponding to a color of the second color system using a lookup table with interpolation, and a second color signal processing means for adjusting a local color space is provided. Characteristic image processing device. 2. An image processing apparatus according to claim 1, wherein said first color signal processing means performs color adjustment by a linear matrix operation method. 3. The first color signal processing means adjusts lightness, saturation, hue, gray balance, and gamma characteristics of the entire color space, and the second color signal processing means adjusts a local color space. The image processing apparatus according to claim 1, wherein brightness, saturation, hue, gray balance, and gamma characteristics of the image processing device are adjusted.