JPH0241271A - Color image forming apparatus - Google Patents

Abstract

PURPOSE:To arbitrarily adjust the intensity or content of a sharpness correction by effecting sharpness-correcting of information only mainly indicating lightness of a Y signal or the like of information representing XYZ table color system by correcting means. CONSTITUTION:An image data source 10 has an image data generation source, and has a function of converting obtained colored data to XYZ table color system and a function of correcting various types of color data. A full-color printer 20 has an image processor 21 having a function of converting image data in input XYZ table color system and function of variably correcting gradation reproduction, color reproduction characteristics, and an image output unit 22 such as a printer for reproducing a color image on the basis of image data from the processor 21. A sharpness correcting circuit 25 for correcting sharpness reproducing characteristic of only Y signal from the source 10 is provided between the source 10 and the printer 20.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a color image forming apparatus such as a full color printer, and more specifically, to a color image forming apparatus that performs sharpness correction on given color information to reproduce and form a color image. Regarding equipment.

[Prior Art 1] A conventional general configuration of a device that reproduces and forms a color image based on provided color information, such as a full color printer system, is shown in FIG. That is,
An image input device 15 such as a scanner optically reads the target input image 5, and various processes such as color correction processing and gradation reproduction processing are performed on the color information corresponding to the read image from the image input device 15 to create a color image. It is equipped with an image processing device 16 for obtaining information, and an image output device 17 such as a printer that reproduces a color image based on the color image information from the image processing device 16 and obtains an output image 8.

In such a full-color printer system, various processes such as image reading and gradation reproduction, color materials used, etc.
Because there are factors that degrade image sharpness,
In order to obtain an output color image 8 that more faithfully reproduces the input color image 5, the image processing device 16 also performs sharpness correction processing to emphasize the edges of the image. Since the color information from the image input device f15 such as a scanner is usually provided as a so-called RGB signal (R: red, G: green, B: blue), the image processing device 16 conventionally includes sharpness correction processing. Each process is performed using the corresponding RGB signal or decoded YMCK signal (Y: yellow, M: magenta,
This is done for each of the following: C Nisian, Ni Black.

[Problems to be Solved by the Invention] In the conventional color image forming apparatus described above, there is a limit to the color reproducibility at the image edge portion.

This is because the sharpness correction processing for emphasizing edge portions is applied to each of the RGB signals, which causes each color component signal to change. Normally, each color signal (
Efforts have been made to ensure that there are no changes when synthesizing R, G, B), but there are limits at present.

Therefore, an object of the present invention is to realize sharpness correction without affecting each color component.

[Means for Solving the Problems] The present invention relates to an apparatus that performs sharpness correction on given color information (A) to reproduce and form a color image, and provides means for solving the above problems in the apparatus. As shown in FIG. 1, the system includes a color system converting means 1 that converts given color information (A) into a color system expression in which lightness appears independently, and the above-mentioned table that is the basis for color image reproduction. A correction means 2 is provided which performs sharpness correction only on information (C) mainly representing brightness among the information (B, C) expressed in the color system obtained by the color system conversion means 1.

The color system to be obtained by the color system conversion means 1 is the XYZ color system (CIE1931XY color system Mataha C■E1964
XY color system), UVW color system (CIE1964U” V
"W" uniform W space), CIELAB uniform space (CI
E1976L"a"b'), etc.A known color system in which lightness appears independently, or a newly defined color system may be used as long as lightness appears independently.

Here, in the XYZ color system, the Y signal itself expresses the brightness, in the UvW color system, L* expressed as L*u*v*, and in the CIELAB uniform space, the L* signal expresses the brightness. It corresponds to

Moreover, the above-mentioned "information mainly representing brightness" means that information corresponding to brightness is the main body and may include other information.

[Operation] For example, RG given from an image input device such as a scanner
The color information (A) given in the format B is converted to a color system converting means 1.
is converted to a color system such as the XYZ color system in which brightness appears independently. xY obtained by this color conversion means 1
In the information (a, C) expressed in a color system such as Z, the correction means 2 performs sharpness-tA mark correction only on information (C) mainly representing brightness, such as a Y signal. Then, color image reproduction is performed based on information (C) representing brightness such as the Y signal sent through the correction means 2 and other information (B) such as the X and z signals from the color system conversion means 1. .

[Example] Embodiments of the present invention will be described below based on the drawings.

FIG. 2 is a block diagram showing an example of the basic configuration of a full color printer system realizing a color image forming apparatus according to the present invention.

In the figure, 10 is an image data source, and this image data source 10 includes an image conversion device 11 such as a television, an image generation device 12 such as various computers, and an image input device H13, 14 such as a scanner or fax. RG of
In addition to having an image data generation source in B format, this RG
It has a function of converting color data obtained in B format into an XYZ color system and various correction processing functions regarding the color data. 20 is a full-color printer, and this full-color printer 20 converts input image data in the XYZ color system into YMCK format (or R
An image processing device 2 which has a function of converting to GB format) and various correction functions of correcting gradation reproduction and color reproduction characteristics.
1, and an image output device 22 such as a printer that reproduces a color image based on YMCK format image data from the image processing device 21. - [A sharpness correction circuit 25 is provided between the image data source 10 and the full-color printer 20 for correcting the sharpness reproduction characteristic only for the Y signal from the image data source 10. There is.

That is, the processing on the image data source 10 side and the processing on the full color printer 20 side are completely separated. As a result, processing related to color correction on the image data source 10 side and the full color printer 20 side can be executed independently. For example, even if the image data generation source is replaced, the color correction system for the entire system can be executed independently. There is no need to rebuild (change various correction coefficients, etc.), and only the change on the image data source 10 side is sufficient.

FIG. 3 shows the system of FIG. 2 divided into specific functional blocks.

The original color image 30 drawn on the original is optically read 31, and the RGBi 11 degree (or brightness) data corresponding to the color of the original 30 obtained through this reading is processed in various ways in the image processing unit/10. After the processing, a color image is reproduced in a printout 46 by a printer 45. In such a processing process, the image processing unit 40 performs a reading characteristic correction function 41, a sharpness correction function 42, a color correction masking processing function 43, and further screen processing, undercolor removal/removal, and Ivi tone correction correction@ It is equipped with various image processing functions 44 such as m processing. The reading characteristic correction function 41 in the image processing unit 40 is a function to convert all RGBII degree data obtained by color image reading 31 into XYZ data in the color system, and is a function that converts all data obtained by color image reading 31 into XYZ data in the color system. This is achieved through processing (for example,
(See Breakfast Bookstore ``The Properties and Techniques of Color,'' etc.) Various coefficients in this arithmetic processing are optimally determined by reading the test image 32 and performing estimation calculations based on the output at that time. Note that the formula for converting from RGB 11 degrees to XYZ is given as follows, for example.

([)RDG, DB): RG B 11 degrees K
: Constant in the RGB 11 degree expression format Also, the color correction masking processing function 43 is used for various image processing 44 and printer 4
5. The printer 45 uses the color information given as XYZ data to perform optimal color reproduction by considering the color reproduction characteristics of all color materials, recording materials, etc. ), and is realized by general linear or quadratic arithmetic processing (for example, see "Properties and Techniques of Color 1, etc.").

Various coefficients in this calculation process are sample color data 4
7 (XYZ data) is directly subjected to masking processing 43, and the optimum one is determined by estimation calculation based on the measured value of printer output 46 at that time. Furthermore, the sharpness correction function 42 performs a reading characteristic correction process 41 to
This is applied only to the Y data that represents brightness among the color information corrected to the data, and the content is similar to general sharpness correction, and the MTF as a whole system is designed to have the desired characteristics. This is achieved using a digital filter. The Y data that has undergone this sharpness correction 42 is then subjected to the color correction masking process 43 described above together with the X and Z data to which the correction is not applied.

In the above functional blocks, the processing before the reading characteristic correction processing function 41 in the image processing unit 40 is realized on the image data source 10 side in FIG. 2, and the processing after the same color correction masking processing function 43 is performed. Same second
This is realized on the full color printer 20 side in the figure.

In a full-color printer system such as the one mentioned above, the color information of the RG8 expression obtained by reading the original 30 is
Since the color expression is converted to the YZ color system, and sharpness correction is performed only on the Y data that represents brightness, the effect of the sharpness correction does not affect the color image, and the reproduced colors are the same as the original 30. more faithful.

In addition, since the processing circuit related to sharpness correction only needs to be configured for brightness information, the circuit configuration is simplified compared to the conventional system that required three processing circuits for R, G, and B. .

In addition, in the above embodiment, the XYZ color system was explained as an example, but
Other color systems, such as UVW color system (C■E1964U
1v*W*uniform space) or (IELAB uniform space ((lE1976L"a"b")), even in known color systems where brightness appears independently, and even in newly defined color systems, the brightness is The same applies if they appear independently.

Figure 4 is drawn as in the above example! & This example does not show that the processing of the reading system and the image output system are separated, but is applied as is to a conventional system.

That is, like the configuration shown in FIG. 5, it includes an image input device 15 for color images, an image processing device 16, and an image output device 17 for reproducing the color image 8. Here, the image processing device 16 includes an image conversion circuit 23 that converts color information in RGB expression corresponding to the input color image 5 from the image input device W115 into color information consisting of brightness V and other components; It has a sharpness correction circuit 24 that corrects the sharpness only for the brightness V signal from the image conversion circuit 23 and the sharpness correction circuit 24, and performs various image processing similar to the conventional one on the color information obtained through the image conversion circuit 23 and the sharpness correction circuit 24. A color correction/gradation correction circuit 26 and a halftone reproduction circuit 27 are provided.

Even in such a system, since sharpness correction is performed for brightness, the effect of the correction processing does not spread to the color image as described above, and the color reproduction of the output color image 8 is faithful to the input color image WA5. Become something.

[Effects of the Invention] As explained above, according to the present invention, sharpness correction is applied to information regarding brightness among the color information provided, so that brightness is uniform and contours occur in saturation and chromaticity. Sharpness correction can be achieved without affecting each color component, such as blurring of reproduced colors or deviations in color reproduction due to sharpness correction in image areas that are currently being processed. Therefore, the color reproducibility at the image edges is further improved.

Since sharpness correction can be performed independently of color reproduction in this way, it becomes possible to arbitrarily adjust the sharpness correction marks and contents, and furthermore, it becomes possible to reproduce color images that are faithful to the original. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the present invention, FIG. 2 is a block diagram showing an example of the basic configuration of a full-color printer system that realizes a color image forming apparatus according to the present invention, and FIG.
FIG. 4 is a diagram showing another application example, and FIG. 5 is a diagram showing an example of the basic configuration of a conventional full-color printer system. 41... Reading characteristic correction processing function 42... Sharpness correction circuit 43... Color correction masking processing function 45... Printer

Claims (1)

[Claims] A device that performs sharpness correction on the given color information (A) to reproduce and form a color image, and a color system that converts the given color information (A) into an expression in a color system in which brightness appears independently. System conversion means (1) and information (C) mainly representing brightness in the color system expression information (B, C) obtained by the color system conversion means (1) which is the basis of color image reproduction. 1. A color image forming apparatus comprising: a correction means (2) that performs sharpness correction only with respect to the image.