JPH0659657A - Image processing device - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to generate a clear monochrome image data from color image data by allowing a halftone image to be expressed in a binary manner in consideration of a difference in hue. To do. [Structure] A plurality of gray tables (TBL corresponding to each hue)
1 to TBLn), a gray table corresponding to the hue of the color image data is selected from these gray tables, and the gray scale corresponding to the luminance is obtained by referring to the gray table. This gradation is converted into a binary image by a dither pattern that expresses light and shade, whereby a halftone image of color image data can be clearly expressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing device,
In particular, the present invention relates to an image processing device for displaying color image data in monochrome.

[0002]

2. Description of the Related Art In recent years, in image processing apparatuses such as computer systems, the price of hardware has been reduced,
Color display configurations that handle color images instead of monochrome display are becoming mainstream.

However, not all computer systems are color-displayed, and it is sometimes necessary to display color image data on a monochrome binary display device.

In this case, since the conventional device does not perform a special process for displaying the color image data on the monochrome display device, for example, all the colors other than black are converted to white, or each color is converted into white. A method of fixedly allocating black and white was adopted.

Therefore, conventionally, it is difficult to display color image data as a clear monochrome image, and in particular, it is difficult to visually recognize the image because halftone expression and hue difference cannot be expressed. There was a problem that became. Further, when printing color image data as monochrome data, such as when making a hard copy of a color display screen, there is a problem that all parts other than white are printed in black.

[0006]

Conventionally, since no special processing for displaying color image data on a monochrome display device has been performed, clear monochrome image data cannot be obtained from the color image data.

The present invention has been made in view of such a point, and a halftone image can be expressed in a binary manner in consideration of a difference in hue so that clear monochrome image data can be generated from color image data. An object is to provide an image processing device.

[0008]

An image processing apparatus according to the present invention is provided with color conversion means for inputting color image data and converting the color image data into hue, brightness, and saturation, and for each hue. , A plurality of gray tables in which the gradation of a binary image corresponding to each luminance value is defined by a predetermined number of gradations, and the hue calculated by the color conversion means from the plurality of gray tables. A gray table is selected, table reference means for obtaining the gradation degree corresponding to the brightness of the color image data by referring to the gray table, and the gradation degree obtained by the table reference means are used for a predetermined gradation expression. Means for converting into a binary image by binary pattern data.

In this image processing apparatus, a plurality of gray tables corresponding to each hue are prepared, and the gray table corresponding to the hue of the color image data is selected from the plurality of gray tables. Therefore, by referring to the gray table, it is possible to obtain the gradation degree corresponding to the luminance in a state in which the hue is taken into consideration. Therefore, by converting this gradation degree into a binary image by using binary pattern data expressing gradation, it is possible to clearly express the halftone image of the color image data as monochrome data.

Further, instead of the gray table in which the gradation is stored, a pattern table in which binary pattern data corresponding to the luminance is stored is provided, and by referring to this pattern table, the 2 Value pattern data may be obtained.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an image processing apparatus according to the first embodiment of the present invention. This image processing device is for converting color image data into monochrome image data and constitutes a part of a computer system.

This image processing apparatus comprises a gray table management module 11, an RGB conversion module 12, a gray table selection module 13, a gray table reference module,
Dither pattern conversion module 15, binary image generation module 16, display 17, printer 18, gray table memory
Equipped with 19.

The gray table management module 11 stores a plurality of gray tables TBL1 ... TBL1 in the gray table memory 19.
Set TBLn. In this case, the gray table is prepared for each of a plurality of hues (red, blue, green, yellow, purple, light blue, gray ...). The number of prepared gray tables, that is, the number of hues is determined by how many hues the color image is divided into, and the number (n) can be selected to any value.

Each gray table (TBL1 to TBLn)
Is the gradation value of the binary image with respect to the brightness value of the color image for a corresponding hue, the predetermined gradation number (for example, 8 bits).
Is defined in.

The reason why the gray table is prepared separately for each hue in this way is because of consideration of the characteristic that different hues have different brightness (brightness) even if the brightness is the same. Is.

The RGB conversion module 12 inputs color image data (RGB data) generated in this computer system or supplied from the outside, and inputs it to hue (HUE), luminance (LUMINESCENCE),
Convert to saturation (SUTURATION). This conversion process is sequentially performed for each pixel of the color image.

The gray table selection module 13 selects the gray table corresponding to the hue extracted by the RGB conversion module 12 from the plurality of gray tables (TBL1 to TBLn) set in the gray table memory 19 as a reference table. select.

In this case, when the saturation extracted by the RGB conversion module 12 is smaller than a predetermined value (gray saturation), the gray table corresponding to gray is selected as the reference table regardless of the hue. To be done. This is because it is appropriate to select a gray table corresponding to gray rather than a gray table corresponding to the hue of the image data, because image data with low saturation has a low correlation between hue and gradation. This is because the furniture is required.

The gray table reference module 14 refers to the gray table selected as the reference table by the gray table selection module 13 and reads the gradation corresponding to the luminance extracted by the RGB conversion module 12. The dither pattern conversion module 15 generates a predetermined dither pattern from the gradation read by the gray table reference module 14.

This dither pattern is
This is a kind of binary pattern data (for example, N × N dots) for expressing the light and shade of an image, and the gradation of the image for N × N dots is, for example, a pseudo-random threshold value given by a Bayer pattern. This is a method of obtaining a pattern of binary data of N / N dots of white / black by comparing with a pattern (N × N dots). In this case, the dots corresponding to the gradation values larger than the threshold value are white, and the dots corresponding to the gradation values smaller than the threshold value are black.

The binary image generation module 16 combines the N × N dot dither patterns obtained by the dither pattern conversion module 15 to generate binary image data corresponding to, for example, one screen of color image data. This binary image data is displayed on the screen of the monochrome display 17 or printed by the printer 18. Next, FIG.
The conversion processing operation from color image data to binary image data by the image processing apparatus of FIG. 1 will be described with reference to the flowchart of FIG.

First, the gray table management module 11 selects gray tables (TBL1 to TBL) corresponding to respective hues.
BLn) are created, and these gray tables are set in the gray table memory 19 (step A1).

At this time, the user gives initial setting data such as how many hues are divided and how many gradations are set, and the gray tables (TBL1 to TBLn) are created based on the initial setting data. To be done.

Next, the color image data (RGB data) is converted into luminance, hue and saturation by the RGB conversion module 12, and the hue and saturation are given to the gray table selection module 13 (step A2).

In the gray table selection module 13, it is judged whether or not the given saturation is larger than a predetermined value (gray saturation) (step A3), and if it is larger, it corresponds to the given hue. The gray table is selected as the reference table (step A4). On the other hand, when the saturation is smaller than the predetermined value, the gray table corresponding to gray is selected as the reference table regardless of the given hue (step A5).

Then, the gray table reference module 14
Refers to the gray table using brightness as an index,
The gradation corresponding to the color image data of N × N dots is obtained, and the dither pattern of N × N dots is generated by the dither pattern conversion module 15 from the gradation (step A6). The N × N dot dither patterns thus obtained are combined by the binary image generation module 16 to generate a binary image for one screen.

As described above, in this embodiment, a plurality of gray tables (TBL1 to TBL) corresponding to respective hues are used.
The gray scale corresponding to the hue of the color image data is selected from n) and the gray scale corresponding to the luminance is obtained by referring to the gray table. Therefore, it is possible to obtain the optimum gradation degree in a state where the difference in brightness due to the difference in hue is taken into consideration. Therefore, by converting this gradation degree into a binary image by a dither pattern that expresses shading, it is possible to clearly express a halftone image of color image data.

In this embodiment, the dither pattern is used as the binary pattern data for the grayscale expression, but it is not limited to this dither pattern, and for example, a density pattern (sometimes called a luminance pattern), etc. It is also possible to use other binary pattern data. In Figure 3,
An image processing apparatus according to a second embodiment of the present invention is shown.

In this image processing apparatus, a dither table (TBL1-1 to 1-n) is provided for each hue instead of the gray table (TBL1 to n) of the first embodiment, and a dither pattern corresponding to brightness is provided. It is a configuration that is stored in each dither table.

That is, in the second embodiment, the dither table management module 11a, the RGB conversion module 12, the dither table selection module 13a, the dither table reference module 14a, the binary image generation module 16, and the display unit 1 are provided.
7, printer 18, gray table memory 19a.

The dither table management module 11a, the dither table selection module 13a and the dither table reference module 14a respectively correspond to the gray table management module 11, the gray table selection module 13 and the gray table reference module 14 of the first embodiment. is there.

A dither table (TB
Each of L1-1 to TBL1-n) defines a dither pattern for the luminance value of the color image for the corresponding hue.

In this case, the dither patterns are set to different patterns when the hue is different for the same luminance. By doing so, it is possible to clearly express a difference in hue on a monochrome image even if the brightness is similar. Also, the dither pattern conversion module 15
Since it is not necessary, the configuration can be simplified as compared with the first embodiment. The conversion process in the second embodiment is also basically executed according to the flowchart of FIG. 2 as in the first embodiment.

[0035]

As described above in detail, according to the present invention,
By referring to the gray table corresponding to the hue of the color image data, the gradation corresponding to the luminance can be obtained in consideration of the hue, and the gradation is represented by a binary pattern. By converting the data into a binary image, the halftone image of the color image data can be clearly expressed as monochrome data.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an image processing apparatus according to a first embodiment of the present invention.

FIG. 2 is a flowchart illustrating a color image data conversion processing operation by the image processing apparatus shown in FIG.

FIG. 3 is a block diagram showing a configuration of an image processing apparatus according to a second embodiment of the present invention.

[Explanation of symbols]

11 ... Gray table management module, 12 ... RGB conversion module, 13 ... Gray table selection module, 14 ... Gray table reference module, 15 ... Dither pattern conversion module, 16 ... Binary image generation module, 19 ... Gray table memory, 19a ... Dither table memory.

Claims (3)

[Claims] 1. Color conversion means for inputting color image data and converting the color image data into hue, brightness, and saturation; and a gradation degree of a binary image provided for each hue and corresponding to each brightness value. A plurality of gray tables each defined by a predetermined number of gradations, and a gray table corresponding to the hue obtained by the color conversion means is selected from the plurality of gray tables, and the gray table is referred to to select the gray table. Table reference means for obtaining a gradation degree corresponding to the luminance of the color image data, and means for converting the gradation degree obtained by the table reference means into a binary image by predetermined binary pattern data for grayscale expression. An image processing apparatus comprising: 2. Saturation detection means for detecting whether or not the saturation obtained by the color conversion means is below a predetermined value, and when the detection means detects that the saturation is below a predetermined value, The image processing apparatus according to claim 1, wherein the table reference means selects a gray table corresponding to gray from a plurality of gray tables. 3. Color conversion means for inputting color image data and converting the color image data into hue, brightness, and saturation, and a predetermined color conversion means provided for each hue and corresponding to each brightness value. A plurality of pattern tables in which each of the binary pattern data is defined, and a pattern table corresponding to the hue obtained by the color conversion means is selected from the plurality of pattern tables.
Table reference means for obtaining binary pattern data corresponding to the brightness of the color image data by referring to the pattern table; and means for generating binary images by combining the binary pattern data obtained by the table reference means. An image processing apparatus comprising: