JP2006237906A - Image processing apparatus and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the saturation of an image signal from being degraded. <P>SOLUTION: The image processing apparatus 30 is provided with: a luminance chrominance separation section 31 for converting an input image signal into a luminance signal and chrominance signals; a luminance conversion section 32 for converting the luminance signal on the basis of at least the chrominance signals and a saturation signal obtained from the chrominance signals; and a recording color conversion section 34 for converting the chrominance signals and the luminance signal into an output image signal depending on an output color reproduction region. Since the luminance signal can be converted only as required by providing limit information of the chrominance signals a*, b* and the saturation signal c* to the luminance conversion section 32, local adjustment can be attained. Thus, saturation degradation and color changes caused by being applied in the unnecessary part of the image signal can be avoided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus and an image processing method.

  2. Description of the Related Art Conventionally, an image processing apparatus that handles images, such as a copying machine, a FAX, or a scanner, has been proposed. Here, for example, when a document image is read by a scanner and the read multi-value image is output by a display or a printer, the density of the background of the document is also reproduced, so that the background of the output image is stained. When the original is a color image, a so-called “fogging” phenomenon occurs in which the ground color is not white.

FIG. 1 is a diagram illustrating a partial configuration of a conventional image processing apparatus. FIG. 2A is a diagram showing a LUT for a character mode, and FIG. 2B is a diagram showing a LUT for a photo mode. As shown in FIG. 1, the image processing apparatus 1 includes an INLUT (lookup table) 2 and a color conversion table (DLUT: direct lookup table) 3. The INLUT 2 performs high brightness adjustment (fogging adjustment) by bringing a table as shown in FIG. 2 into contact with the brightness signal (L *). For example, in the character mode, a table such as that shown in FIG. 2A is abutted, and reproduction of high brightness is suppressed in order to emphasize the character. In the photo mode, a table as shown in FIG. 5B is abutted, and the reproduction method on the high brightness side is changed so that the light color portion can be reproduced. The DLUT 3 performs data conversion from L * a * b * to YMCK for binary image quality. Such a conventional technique is proposed in Patent Document 1.
Japanese Patent Laid-Open No. 7-212583

  However, in the above-described conventional method, INPUT 2 is applied to all regions of the lightness signal L *. Therefore, INPUT 2 is also applied to regions that do not require adjustment on the same L * plane. It becomes.

  FIGS. 3A and 3B are diagrams for explaining other conventional problems. FIG. 3A is a diagram for explaining gamut, FIG. 3B is a diagram for explaining INLUT, and FIG. When the lightness signal L * is in contact with the entire area, the data that has not been reproduced by the output device (outside the gamut) is mapped to the outer wall of the gamut as shown in FIG. There is a problem that the degree of degradation occurs. These problems cannot be solved by the technique described in Patent Document 1.

  Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide an image processing apparatus and an image processing method capable of preventing a decrease in saturation.

  In order to solve the above problems, the present invention provides a first conversion means for converting an input image signal into a lightness signal and a chromaticity signal, and at least one of the chromaticity signal and the chromaticity signal obtained from the chromaticity signal. Based on the second conversion means for converting the lightness signal converted by the first conversion means, the chromaticity signal and the lightness signal converted by the second conversion means are converted into an output image signal depending on an output color reproduction range. And an image processing apparatus including a third conversion unit. According to the present invention, the lightness signal can be converted only when necessary by giving the restriction information of the chromaticity signals a *, b * or the saturation signal c * to the means for converting the lightness signal. Adjustment is possible. For this reason, it is possible to avoid saturation reduction and color change due to application in unnecessary portions.

  The second conversion unit is configured such that when at least one of the chromaticity signal converted by the first conversion unit and the chromaticity signal obtained from the chromaticity signal converted by the first conversion unit is equal to or greater than a predetermined value, The lightness signal converted by the first conversion means is not converted. According to the present invention, it is possible to avoid saturation reduction and color change due to application in unnecessary portions.

  The second conversion means has a plurality of lookup tables for converting the lightness signal. Thereby, the degree of freedom of local adjustment increases by increasing the number of lookup tables for converting the brightness signal.

  The second conversion means includes a plurality of look-up tables for converting the lightness signal, and the plurality of looks according to at least one of the chromaticity signal and a saturation signal obtained from the chromaticity signal. A lookup table to be used is selected from the lookup tables. As a result, a plurality of lookup tables for converting the lightness signal are prepared. Depending on the chromaticity signal such as a * and b * or the saturation signal of c *, for example, the lookup table used for the lightness signal conversion is prepared. By switching, the brightness signal can be further converted locally. Thereby, local emphasis etc. are also attained.

  The apparatus further comprises fourth conversion means for converting the chromaticity signal and the brightness signal converted by the second conversion means, and the third conversion means converts the signal converted by the fourth conversion means into the output image signal. It is characterized by doing.

  The present invention provides a first step of converting an input image signal into a lightness signal and a chromaticity signal, and a conversion in the first step based on at least one of the chromaticity signal and a saturation signal obtained from the chromaticity signal. And a third step of converting the chromaticity signal and the lightness signal converted in the second step into an output image signal depending on an output color reproduction range. . According to the present invention, the lightness signal can be converted only when necessary by giving the restriction information of the chromaticity signal a *, b * or saturation signal c * to the means for converting the lightness signal. Local adjustment is possible. For this reason, it is possible to avoid saturation reduction and color change due to application in unnecessary portions.

  In the first step, when at least one of the chromaticity signal converted in the first step and the chromaticity signal obtained from the chromaticity signal converted in the first step is equal to or greater than a predetermined value, The converted lightness signal is not converted. According to the present invention, it is possible to avoid saturation reduction and color change due to application in unnecessary portions.

  The present invention includes a step of selecting a look-up table used for conversion of the lightness signal from a plurality of look-up tables according to at least one of the chromaticity signal and a saturation signal obtained from the chromaticity signal. It further has these. According to the present invention, a plurality of look-up tables for converting a lightness signal are prepared and used for conversion of a lightness signal in accordance with, for example, a chromaticity signal such as a * and b * or a saturation signal such as c *. By switching the look-up table, the brightness signal can be further converted locally. Thereby, local emphasis etc. are also attained.

  ADVANTAGE OF THE INVENTION According to this invention, the image processing apparatus and image processing method which can prevent a saturation fall can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described. FIG. 4 is a schematic block diagram of the copying machine 10 according to the present embodiment. As shown in FIG. 4, the copying machine 10 includes an image input unit 20, an image processing unit 30, and an image output unit 40. The image input unit 20 converts an input image obtained by reading a document placed on the platen glass into digital image data (image signals) of red, green, and blue color components. For example, light from a light source having a halogen lamp irradiates a document placed on a platen glass, and the opposite light is split into red, green, and blue colors via an optical system (not shown). Each color light is incident on a line sensor (image sensor) composed of, for example, a CCD (solid-state imaging device) divided for each color light, and an input image is read at a resolution of, for example, 400 dpi (400 dots / 1 inch). Thus, analog image data of each color component of red, green, and blue is obtained.

  Further, in a predetermined signal processing unit, an amplifying unit (not shown) amplifies red, green, and blue image data from the line sensor to a predetermined level, and an A / D converter (not shown) converts the data into digital data. , Red, green and blue digital image data R, G and B are obtained from the A / D converter. The red, green, and blue image data R, G, and B are sent to the image processing unit 30 through a cable.

  The image processing unit 30 turns on / off yellow (Y), magenta (M), cyan (C), and black (K) based on the red, green, and blue image data R, G, and B from the image input unit 20. A binarized toner signal is obtained and each toner signal is output to the image output unit 40. The image output unit 40 includes image forming units for each color of Y, M, C, and K, which are juxtaposed sequentially at a constant interval in one direction.

  The image processing unit 30 includes a lightness / chromaticity separation unit 31, a lightness conversion unit 32, a lightness / chromaticity conversion unit 33, and a recording color conversion unit 34. The lightness and chromaticity separation unit 31 converts the input image data R, G, and B of red, green, and blue from the image input unit 20 into a lightness signal L * in a uniform color space and a chromaticity signal a * representing saturation and hue. Separated into b * and converted.

  The lightness conversion unit 32 has a plurality of look-up tables (INLUTs) for converting the lightness signal L * into a predetermined lightness signal L * (1). From the chromaticity signals a * and b * and the chromaticity signal, Based on at least one of the obtained saturation signals C *, the lightness signal L * converted by the lightness and chromaticity separation unit 31 is converted. For example, when at least one of the chromaticity signal converted by the lightness / chromaticity separation unit 31 and the saturation signal obtained from the chromaticity signal converted by the lightness / chromaticity separation unit 31 is equal to or less than a predetermined value, the lightness conversion unit 32 When the setting INLUT is applied and the predetermined value is exceeded, the lightness signal converted by the lightness and chromaticity separation unit 31 is not converted. Note that the number of chromaticity signals a * is increased, for example, by increasing the number of planes of the INCUT, such as using the look-up table 1 when X> C *> 0, and using the look-up table 2 when Y> C *> X. , B * or saturation signal c *, a finer adjustment is possible by using different look-up tables.

  Further, the lightness conversion unit 32 has a plurality of INLUTs for converting lightness signals as shown in FIG. 5, for example, and as shown in FIG. 5A, when the chromaticity signal a * ≦ ± 10. Only, the brightness signal L * is applied to the brightness signal L * to convert the brightness signal. Further, as shown in FIG. 5B, only when the chromaticity signal a * ≦ ± 10 and the chromaticity signal b * ≦ ± 10, the lightness signal is converted by applying the INRUT to the lightness signal L *. You may do it.

  The lightness and chromaticity conversion unit 33 uses the chromaticity signals a * and b * and the lightness signal L * (1) converted by the lightness conversion unit 32 and the chromaticity signals a * (1) and b * suitable for the image output unit 40. (1) The signal is converted into a lightness signal L * (11). The recording color conversion unit 34 converts the chromaticity signals a * (1), b * (1) and the lightness signal L * (11) into output image data depending on the output color reproduction range. That is, the lightness signal L * (11) and the chromaticity signals a * (1) and b * (1) converted by the lightness / chromaticity conversion unit 31 are converted into yellow (Y), magenta (M), cyan (C), And black (K) image data. The image output unit 40 forms a color image on, for example, a recording sheet in accordance with the YMCK image data input from the recording color conversion unit 34.

  Next, the operation of the image forming apparatus will be described. FIG. 6 is an operation flowchart of the copying machine 10 according to the present embodiment. In step S1, the image input unit 20 converts an input image obtained by reading a document placed on a platen glass into digital image data of red, green, and blue color components. In step S2, the lightness and chromaticity separation unit 31 uses the red, green, and blue input image data R, G, and B from the image input unit 20 as the lightness signal L * in the uniform color space, and the chromaticity representing the saturation and hue. Separated into signals a * and b * for conversion. In step S3, the lightness conversion unit 32 refers to at least one of the chromaticity signals a *, b * and the saturation signal C * obtained from the chromaticity signal, and the lightness signal L converted by the lightness / chromaticity separation unit 31. * Convert.

  In step S4, the lightness chromaticity conversion unit 33 uses the chromaticity signals a * (1) suitable for the image output unit 40 as the chromaticity signals a * and b * and the lightness signal L * (1) converted by the lightness conversion unit 32. ), B * (1) and lightness signal L * (11). In step S5, the recording color conversion unit 34 converts the lightness signal L * (11) and the chromaticity signals a * (1) and b * (1) converted by the lightness / chromaticity conversion unit 31 to yellow (Y) and magenta. (M), cyan (C), and black (K) image data are converted. In step S <b> 6, the image output unit 40 forms a color image on recording paper or the like according to the YMCK image data input from the recording color conversion unit 34.

  As described above, restriction information such as the chromaticity signals a * and b * or the saturation C * is given to the lightness conversion unit 32, and the lightness signal L * is locally abutted against the INCUT. By converting the lightness signal only to, local adjustment becomes possible. This avoids saturation reduction and color change due to application in unnecessary portions. In particular, high brightness adjustment (fogging adjustment) may be performed only in a portion where a * b *, which is the color gamut of the original paper, is within about ± 10, and adjustment in a region beyond that is unnecessary. For this reason, it is possible to prevent a decrease in saturation that occurs by applying the INRUT in a region other than the above. Also, many look-up tables for converting the lightness signal are prepared. For example, the look-up table used for the lightness signal conversion is switched according to the restriction information of the lightness signals a *, b * or the saturation signal c *. Thus, the brightness signal can be further converted locally. This enables local enhancement. The lightness / chromaticity separation unit 31 corresponds to the first conversion unit, the lightness conversion unit 32 corresponds to the second conversion unit, the lightness / chromaticity conversion unit 33 corresponds to the fourth conversion unit, and the recording color conversion unit 34 corresponds to the third conversion unit. .

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications, within the scope of the gist of the present invention described in the claims, It can be changed.

It is a figure which shows the structure of a part of conventional image processing apparatus. (A) is a diagram showing a LUT for a character mode, and (b) is a diagram showing a LUT for a photo mode. It is a figure explaining other conventional problems. 1 is a schematic block diagram of a copying machine 10 according to the present embodiment. It is a figure which shows the example of INLUT. 3 is an operation flowchart of the copier 10 according to the present embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Copier 20 Image input part 30 Image processing part 31 Lightness chromaticity separation part 32 Lightness conversion part 33 Lightness chromaticity conversion part 34 Recording color conversion part 40 Image output part

Claims (8)

First conversion means for converting an input image signal into a lightness signal and a chromaticity signal;
Second conversion means for converting the lightness signal converted by the first conversion means based on at least one of the chromaticity signal and the saturation signal obtained from the chromaticity signal;
An image processing apparatus comprising: third conversion means for converting the chromaticity signal and the brightness signal converted by the second conversion means into an output image signal depending on an output color reproduction range. The second conversion means is configured to output the first signal when at least one of a chromaticity signal converted by the first conversion means and a saturation signal obtained from the chromaticity signal converted by the first conversion means is equal to or greater than a predetermined value. The image processing apparatus according to claim 1, wherein the brightness signal converted by the one converting unit is not converted. The image processing apparatus according to claim 1, wherein the second conversion unit includes a plurality of lookup tables for converting the brightness signal. The second conversion means includes a plurality of look-up tables for converting the lightness signal, and the plurality of looks according to at least one of the chromaticity signal and a saturation signal obtained from the chromaticity signal. The image processing apparatus according to claim 1, wherein a lookup table to be used is selected from the lookup tables. A fourth conversion means for converting the chromaticity signal and the brightness signal converted by the second conversion means;
The image processing apparatus according to claim 1, wherein the third conversion unit converts the signal converted by the fourth conversion unit into the output image signal. A first step of converting an input image signal into a brightness signal and a chromaticity signal;
A second step of converting the lightness signal converted in the first step based on at least one of the chromaticity signal and a saturation signal obtained from the chromaticity signal;
A third step of converting the chromaticity signal and the brightness signal converted in the second step into an output image signal depending on an output color reproduction range. In the first step, when at least one of the chromaticity signal converted in the first step and the chromaticity signal obtained from the chromaticity signal converted in the first step is equal to or greater than a predetermined value, The image processing method according to claim 6, wherein the converted brightness signal is not converted. Selecting a lookup table to be used for conversion of the brightness signal from a plurality of lookup tables according to at least one of the chromaticity signal and a saturation signal obtained from the chromaticity signal; The image processing method according to claim 6.

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