JPH0528236A - Color picture processor - Google Patents

Abstract

PURPOSE:To reproduce only a part whose background color is light to be white and to reproduce only a chromatic color whose picture part is light into an original picture as it is by providing a means extracting plural color components and a means converting a color picture signal into a specified color signal when all the color components have values within a prescribed range. CONSTITUTION:Recording signals which are color-corrected are inputted to a gamma correction part, and the recording signals shown by digital signals of eight bits are inputted to comparators 51-54 for respective colors. In such a case, a decision result for four colors C, M, Y and K is inputted to an AND circuit 59 and a gray judgement result data S is obtained. Namely, gray decision result data S judges the color to be gray which is to be converted into white when all the four colors are less than a prescribed level. The gray decision result data S controls respective color signals to '0' by using AND circuits 55-58. Since all the recording signals are not restricted to '0' when even one color exceeds the prescribed level, the chromatic color composed of the light component can faithfully be recorded and reproduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image processing apparatus for controlling a color reproduction range by inputting a color image signal.

[0002]

2. Description of the Related Art Conventionally, a digital color copying machine has been known as one of color image processing apparatuses of this type. In this digital color copying machine, image signal control such as so-called color correction / γ conversion is performed for the purpose of faithfully reproducing the color of the original. However, if only the faithful reproduction of the original color is emphasized, the gray color will be reproduced even if the original background color is a little gray, so from the standpoint of a color copier. However, it is hard to say that high quality image reproduction is performed.

Therefore, in order to reproduce and record the background color, it is usual to convert the image data so that the recording signal becomes "white" by so-called γ correction.

[0004]

However, such .gamma.-correction is actually performed on the recording signals of the recording colors C (cyan), M (magenta), Y (yellow), and K (black). This is to correct the linearity of the color density recorded in (1), and to correct image signals below a certain level, which is considered to be the background color of the document, to "0" at a constant rate.

Therefore, although the background portion of the original which is slightly grayish can be reproduced in a whiter and so-called background-free state, chromatic colors such as very pale yellow-green and orange in the image are simply reproduced in yellow. There is a problem that it will end up.

That is, pale yellowish green can be expressed by mixing the Y component, which is the recording color, with the C component having a low signal level, and light orange can be expressed by mixing the Y component with the M component, which has a low signal level. Yes, but the above level is small C
The components and the M component are limited to "0" because it is desired to record the ground color as "white", and as a result, the disadvantage that these pale colors are not expressed occurs.

Accordingly, in view of the above points, the object of the present invention is to
It is an object of the present invention to provide a color image processing apparatus configured to reproduce only a light-colored portion in white and to reproduce a light chromatic color in an image portion as an original image.

[0008]

A color image processing apparatus according to the present invention comprises means for inputting a color image signal to extract a plurality of color components, and all of the plurality of color components having values within a predetermined range. And a means for converting the color image signal into a specific color signal.

[0009]

According to the present invention, a predetermined color (for example, light gray) is detected from the color image signal, and the recording signal is controlled according to the result, so that the image signal is controlled to be whiter only in the light gray area. It is possible to suppress the fog of the background and reproduce the image, and for the image area having a tint, it is possible to reproduce the image with a color more faithful to the original.

[0010]

EXAMPLES Examples of the present invention will be described in detail below.

Embodiment 1 FIG. 1 shows an overall block diagram in an embodiment of the present invention. In the figure, an image reading signal color-separated by RGB color filters (not shown) is supplied from the image sensor 1 to the shading correction unit 2. Here, the sensitivity variation in each cell of the sensor 1 and the light amount unevenness of the light source / imaging system are corrected so that a uniform image can be read as uniform image data.

The input masking section 3 performs color correction from the spectral characteristics of the color filters constituting the sensor 1 and the light emission characteristics of the light source into image signals in a standardized color space. The corrected signal is output to a peripheral device such as an external computer and also input to the color correction / UCR (undercolor removal) unit 4.

The color correction / UCR unit 4 logarithmically converts the luminance signal into the density signal, and then corrects the "cloudiness" of the color of the recording paper / recording material used in the recording unit 6 on the image signal. further,
A black component is generated to reproduce black more faithfully, and at the same time, the black component is removed from the CMY signal.

The color-corrected recording signal is input to the γ correction unit 5 peculiar to this embodiment.

FIG. 2 shows γ which is generally used conventionally.
It shows the correction characteristics, and when each color signal is below a predetermined K level, the output value is set to 0 to prevent "background fog", and the linearity of the recording apparatus for the recording area, that is, the level from K to 255. In order to guarantee that, non-linear data conversion is performed and correction is performed.

Next, the gamma correction unit 5 in this embodiment will be described in detail with reference to FIG.

In FIG. 3, a recording signal represented by an 8-bit digital signal is compared for each color with a comparator 51,
52, 53, 54 are input to determine whether or not the value is less than or equal to a predetermined value K, the determination results for the four colors are input to the AND circuit 59, and gray determination result data S is obtained. In other words, the gray determination result data S is S = when all of C, M, Y and K are K or less.
0 ... determined as gray to be converted to "white" (1) In other cases, S = 1 ... (2) This gray determination result data S (1 bit) is output from AND circuits 55, 56, 57 and 58. Each color signal is controlled to "0" by using this. For example, the output value of the C signal becomes 0 only when S = 0, and in S1, the C signal is directly input to the γ conversion ROM 50-1 and the value of 0 to 255 is input based on the non-linear characteristic shown in FIG. Are all converted.

As described above, the characteristic feature of the present embodiment is that even one color in the image signal just read out has level K.
In the case of exceeding, the recording signal is not limited to "0" as in the conventional example, so that the chromatic color composed of the light component can be more faithfully recorded and reproduced. Note that the AND gates 55 to 5 can be used only when light gray is detected.
8 equivalently implements the same recording limitation as in the conventional example as a line in FIG.

Embodiment 2 FIG. 5 shows another embodiment of the γ correction unit 5. Example 1 described above
In the above, the recording signal below the level K is discontinuously controlled to "0" by the gray judgment result data S, but in the present embodiment,
By using an LUT (look-up table), whiter and more continuous whitening is possible.

That is, in FIG. 5, the γ conversion ROM 50
1-1, 501-2, 501-3, 501-4 input the gray judgment result data S to the input address terminals thereof, and as shown in FIG. 6, when the image is not light gray (S =
(In the case of 1), the linearity of the recording device is corrected and recorded over the entire range of the level of the recording signal from 0 to 255, and when the image is a light gray color (in the case of S = 0), K to 0 for the level K or less.
The areas between are continuously emphasized in white to enable record reproduction.

Although the constant K has been described as a value common to all colors in the above-described embodiments, it may be set independently for each color, or may be a value that should be varied in association with a so-called density lever or the like. Not to mention.

Embodiment 3 While the above-mentioned two embodiments detect gray from CMYK signals, a third embodiment for detecting gray more accurately is shown in FIG.

In FIG. 7, the L ^* a ^* b ^* converter 502 is shown.
Is for converting the RGB luminance data color-corrected by the input masking unit 3 in FIG. 1 into the L ^* a ^* b ^* space defined by CIE. That is, since L ^* defined by CIE is a value indicating brightness and a ^* b ^* is a value indicating hue, the comparator 503 first thresholds L ^* with a constant K2, and Degree

[0024]

[Equation 1]

## EQU3 ## The threshold value is processed by a constant K1,
Detects light gray.

That is, the judgment of light gray is

[0027]

[Equation 2] L ^* > K2 and

[0028]

[Equation 3]

When is S = 0 gray otherwise S = 1
Becomes

The AND circuit 505 obtains the determination signal S = 0 only in the case of light gray which satisfies the above two conditions. The control of the recording signal using this determination signal is the same as that of FIG. 5, and thus the description thereof is omitted.

As shown in this embodiment, so-called "white"
In order to detect a gray color close to, there is no limitation to the method presented herein, and other color spaces such as CIE RGB, XYZ,
The same can be done by using color coordinates such as LUV and HUC.

Further, in order to achieve the purpose of preventing the background fog of the reproduced image by emphasizing it to "white" only when the background color is a light gray color, in addition to the cases shown in the above-mentioned respective embodiments, the color correction is performed. If there is a one-to-one correspondence with a recording color such as RGB or logarithmic conversion, the processing is not limited to processing only for CMYK recording signals.

Embodiment 4 In the above-mentioned embodiment, the processing is switched to two kinds according to the binary judgment as to whether or not it is light gray, but more smoothly (that is, continuously).
For the processing, the light gray color is accurately determined in two steps or three steps, and accordingly, the intermediate state of the two characteristics shown in FIG.

The recording method used in the present invention is not limited.

[0035]

As described above, according to the present invention, by detecting a predetermined color (for example, light gray), the portion of the predetermined color (light gray portion) is converted into another color (for example, white). As a result, the background color of the original can be removed, while the other pale chromatic colors can be reproduced more faithfully.

[Brief description of drawings]

FIG. 1 is a block diagram showing an entire embodiment of the present invention.

FIG. 2 is a diagram showing a general γ correction characteristic.

FIG. 3 is a detailed circuit diagram of a γ correction unit in the present embodiment.

FIG. 4 is a diagram showing input / output characteristics of the γ conversion ROM 50 shown in FIG.

FIG. 5 is a circuit diagram showing a second embodiment of a γ correction unit 5.

6 is a diagram showing an input / output characteristic of a γ conversion ROM 501 shown in FIG.

FIG. 7 is a block diagram showing a third embodiment of the present invention.

[Explanation of symbols]

1 image sensor 2 Shading correction section 3 Input masking section 4 color correction / UCR section 5 γ correction unit 6 recording section 51-54 Comparator 59 AND circuit S Gray judgment result data 56-58 AND circuit 50-1 to 50-4 γ conversion ROM 501-1 to 501-4 γ conversion ROM 503,504 Comparator

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04N 9/64 8942-5C 9/75 8626-5C

Claims (2)

[Claims] 1. A means for inputting a color image signal to extract a plurality of color components, and when all of the plurality of color components have values within a predetermined range, the color image signal is converted into a specific color signal. A color image processing apparatus comprising: 2. The color image processing device according to claim 1, wherein when the color image signal has a light gray color component, the color image signal is converted into a white color signal.