JP3556732B2 - Color image processing equipment - Google Patents

Abstract

PURPOSE: To improve picture quality by suppressing the bleeding of a reproduced color and the occurrence of slippage in color reproduction. CONSTITUTION: An edge emphasis circuit 1 performs the edge emphasis of a G signal, and outputs a signal Ge. Signals R, G and B and the signal Ge are inputted to a first correction circuit 2, and correction to equalize (R:G:B=R': G':B') the ratio of colors of the signals before and after the edge emphasis is performed. A second correction circuit 3 comprises a maximum value circuit, an input/output ratio generation circuit and a multiplier, and performs the correction so as to obtain relation R':G':B'=R0:G0:B0. In this way, it goes to R:G:B=R0:G0:B0, which equalizes the ratio of each color of an input/output signal.

Description

[0001]
[Industrial applications]
The present invention relates to a color image processing apparatus that suppresses the occurrence of bleeding of reproduced colors and a shift in color reproduction and improves image quality.
[0002]
[Prior art]
2. Description of the Related Art In recent years, there has been an increasing number of opportunities to copy a document using a color copying machine, read a document from a color scanner, and output the document using a color printer. When an original is read from a color scanner including a color copying machine, the sharpness of the original is reduced due to the MTF characteristics of the scanner. Therefore, it is necessary to correct the sharpness. In order to correct the sharpness, an edge enhancement process is usually used. However, the edge enhancement processing has various problems as described below.
[0003]
1. Normally, the edge enhancement is performed with respect to a color image signal at a position corresponding to each coefficient, as shown in FIGS. And weighted by the above coefficient. The results are all added and become an edge-emphasized signal. This edge enhancement circuit requires a relatively large-scale device for multiplying an image signal by a weight or adding a multiplication result. For example, when it becomes necessary to perform edge enhancement on an RGB color image signal at the same time, three edge enhancement circuits are required, which significantly increases the cost.
[0004]
2. The CCD line sensor used in the scanner has a structure as shown in FIGS. 11 (a) and 11 (b). (A) is a one-line sensor, and (b) is a three-line sensor. Due to such a structure, each output of the CCD line sensor is misaligned, and it is necessary to correct this and align each color signal. However, this positioning is performed digitally, and its accuracy is limited. Further, the sharpness may be different for each color signal due to variations in the MTF characteristics of the sensors for each color. For the reasons described above, when trying to correct the sharpness with the same strength for each color, the color balance collapse and the difference in sharpness due to misregistration for each color are emphasized, and the occurrence of bleeding of reproduced colors and deviation of color reproduction may occur. And the image quality deteriorates.
[0005]
3. Further, the following can be cited as other causes of bleeding of reproduced colors and deviation of color reproduction. This will be described with reference to FIG. When the output signal of the edge emphasis circuit is, for example, 8 bits, the output is usually limited to 0 or more and 255 or less (see, for example, Japanese Patent Application Laid-Open No. 4-13833). If the value exceeds this range during sharpness correction, a value less than 0 is clipped to 0 and a value greater than 255 is clipped to 255. (A) is RGB image data before edge enhancement. When edge enhancement is applied to this image data, the image data becomes (b). When the data of 255 or more and the data of 0 or less in the edge-enhanced image data are clipped, the image data becomes the image data shown in FIG. When this state occurs in at least one color of the RGB signal, the balance of the RGB signal is greatly lost, and the RGB signal is reproduced in a manner significantly different from the original color.
[0006]
[Problems to be solved by the invention]
In order to solve the first problem, for example, JP-A-61-273073 (first publication), JP-A-62-149264 (second publication), and JP-A-4-149383 (first publication) 3 publication).
[0007]
The edge enhancement device described in the first publication extracts lightness information from a color image signal expressed in density, generates a signal indicating the degree of edge enhancement from the brightness information, and generates a signal indicating the degree of edge enhancement. Outputs the result according to the level. Further, the image contour enhancement device described in the second publication calculates Laplacian from image data of at least one color of a color image signal, and adds the Laplacian to the image signal to enhance the contour. The image processing device described in the third publication calculates a filter signal from image data of at least one color of a color image signal, and corrects the image signal based on the filter signal.
[0008]
Each of the publications described above uses a circuit for detecting an edge component of a signal of one color without using three edge enhancement circuits, and adds or multiplies the output to a color signal to obtain an edge. The method of emphasizing is adopted.
[0009]
To solve the above two problems, for example, JP-A-3-102578 (fourth publication) and JP-A-4-170267 (fifth publication) are mentioned. The fourth and fifth methods convert an RGB signal into an L * a * b * signal, perform sharpness correction (edge emphasis) only on L *, and then apply L * a * b * to the L * a * b * signal. Inverse conversion into RGB signals or conversion into CMY signals.
[0010]
However, the techniques described in the above-mentioned first to third publications do not solve the above three problems (use a limiter circuit or do not mention this problem), and However, the techniques described in the fourth and fifth publications have the following problems.
[0011]
FIG. 9 shows the reproduction range of the output device expressed in L * a * space of L * a * b * space for convenience. That is, in the L * a * b * space, the range of L * that can be taken differs depending on the value of a * b *. Therefore, if L * a * b * after the sharpness correction is located outside this color space, the conversion from L * a * b * to RGB or CMY is outside the range of the conversion table, so that RGB or CMY is used. It may be converted to a value outside the range that can be taken in space. As a result, the above three problems arise here.
[0012]
Therefore, in order to avoid this problem, there is a method in which the boundary of the L * a * b * reproduction range is used as a table at the time of sharpness correction. However, this method requires a huge amount of data, and each output device has its own color reproduction range, and it is necessary to prepare a table corresponding to the color reproduction range. Leads to an increase in
[0013]
The present invention solves the above three problems,
SUMMARY OF THE INVENTION It is an object of the present invention to provide a low-cost color image processing apparatus which suppresses the occurrence of bleeding of reproduced colors and a shift in color reproduction to improve image quality and reduce the scale of the apparatus.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, an edge enhancing means for performing edge enhancement on at least one color signal of a digital color image signal, a signal before edge enhancement and a signal after edge enhancement. A first correction unit that corrects the digital color image signal based on the first and second correction units; and a determination unit that determines whether a signal of at least one color among the corrected signals exceeds a predetermined value. A second correction unit that corrects the signal after the correction in accordance with the determination result, wherein the first correction unit determines that each of the color ratios of the signal input to the first correction unit and the output signal is It is characterized in that correction is performed so as to be equal .
According to the second aspect of the present invention, an edge enhancing means for performing edge enhancement on at least one color signal of the digital color image signals, and the digital color image signal based on a signal before edge enhancement and a signal after edge enhancement. First correcting means for correcting a signal, determining means for determining whether at least one of the signals of the corrected signal exceeds a predetermined value, and performing the correction in accordance with the determination result A second correction unit that corrects a subsequent signal, wherein the first correction unit converts a ratio value between the color signal after the edge enhancement and the color signal before the edge enhancement into each of the other color signals. The multiplication signal and the color signal after the edge enhancement are corrected so as to be output as corrected signals .
According to the third aspect of the present invention, the digital color image signal is obtained based on an edge enhancing means for performing edge enhancement on at least one color signal of the digital color image signal, and a signal before edge enhancement and a signal after edge enhancement. First correcting means for correcting a signal, determining means for determining whether at least one of the signals of the corrected signal exceeds a predetermined value, and performing the correction in accordance with the determination result A second correction unit that corrects a subsequent signal, wherein the second correction unit performs correction such that each color ratio of a signal input to the second correction unit and a signal output from the second correction unit become equal. It is characterized by:
According to the fourth aspect of the present invention, the digital color image signal is obtained based on a signal before edge enhancement and a signal after edge enhancement based on edge enhancement means for performing edge enhancement on at least one color signal of the digital color image signal. First correcting means for correcting a signal, determining means for determining whether at least one of the signals of the corrected signal exceeds a predetermined value, and performing the correction in accordance with the determination result A second correction unit that corrects a signal after the correction, wherein the second correction unit determines the predetermined value and the signal after the correction when the determination unit determines that the signal exceeds a predetermined value. Is corrected so as to output a signal obtained by multiplying the value of the ratio with the maximum value of the signal by the corrected signal .
[0015]
[Action]
The first correction unit corrects the signals after the edge enhancement and before the edge enhancement so that the color ratios become equal. As a result, blurring of reproduced colors and deviation of color reproduction, which are the two problems, are less likely to occur, and image quality is improved. The correction method of the first correction means is a correction method in which, if a signal after edge enhancement is determined for one color, another color is determined, it can be constituted by one edge enhancement circuit. That is, this solves the first problem. Further, in the second correction means, the ratio of each color of the input signal and the output signal is made equal, and the ratio is set within the range of possible values of the output signal. Thereby, the above three problems are solved.
[0016]
【Example】
Hereinafter, an embodiment of the present invention will be specifically described with reference to the drawings.
FIG. 1 shows the configuration of an embodiment of the present invention. In the figure, 1 is an edge enhancement circuit, 2 is a first correction circuit, 3 is a second correction circuit, 4, 5 and 6 are comparators, and 7 is an OR circuit.
[0017]
An 8-bit RGB color image signal digitally input from a color scanner or the like becomes an input signal (note that the numbers “8” to “9” on the R, G, and B lines represent 8 to 9 bits). ). The edge enhancement circuit 1 performs edge enhancement on the G signal of the input signals.
[0018]
FIG. 2 shows the configuration of the edge enhancement circuit. The edge enhancement circuit includes line memories 8 and 9, a weighting adder 10, a multiplier 11 and a limiter 12. The line memories 8 and 9 sequentially store the G data of the (n + 1) th line and the G data of the nth line, respectively. The G data of the (n + 2) th line which is directly input to the weighting adder 10 and the line memories 8 and 9 Is weighted and added with the filter mask of FIG. The multiplier 11 multiplies the value of the target pixel subjected to edge enhancement (that is, the pixel located at the mask coefficient “5”) by an intensity coefficient for adjusting the intensity of edge enhancement. In the case of the present embodiment, the intensity coefficient is 1, and in the case of FIG. 12B, the intensity coefficient is １ ／. Further, the limiter 12 clips the lowest value to 0 and the highest value to 255 to make the output signal 8 bits.
[0019]
Let the signal after edge enhancement be Ge. The RGB signal and the Ge signal are input to the first correction circuit 2. FIG. 3 shows the configuration of the first correction circuit. The first correction circuit includes a comparator 17 for comparing the G data with 0, a selector 13 for selecting Ge or G according to the comparison result of the comparator 17, and an input / output according to the comparison result of the comparator 17. It comprises an input / output ratio generation circuit 14 for generating a ratio (1 or Ge / G), and multipliers 15 and 16 for multiplying the output of the input / output ratio generation circuit 14 and R and B data.
[0020]
When the G signal is not 0 and when it is 0, the comparator 17 compares the G signal with 0 to switch the correction method. The comparator 17 outputs 1 when G is equal to 0, and outputs 0 when G is not equal to 0. The output of the comparator 17 is input to and controls the input / output ratio generation circuit 14.
[0021]
That is, if the output of the comparator 17 is 1 (G = 0), the input / output ratio generation circuit 14 outputs 1, and if the output of the comparator 17 is 0 (G ≠ 0), the input / output ratio generation circuit 14 Outputs Ge / G. The multipliers 15 and 16 multiply the output of the input / output ratio generation circuit 14 by the R and B signals, respectively, and output R ′ (= R × (Ge / G)), B, which is the output signal of the first correction circuit 2. '(= B × (Ge / G)) signal is output.
[0022]
When the output of the comparator 17 is 1, the selector 13 selects and outputs G, and when the output of the comparator 17 is 0, the selector 13 selects and outputs Ge. The output of the selector 13 is a G ′ (G or Ge) signal that is an output signal of the first correction circuit 2. Therefore, when G ≠ 0, the R component is edge-emphasized to R × (Ge / G), and the B component is similarly edge-emphasized to B × (Ge / G). Then, in the first correction circuit, the ratio of each color between input and output is equal because R: G: B = R ′: G ′: B ′.
[0023]
Returning to FIG. 1, the R'G'B 'signal output from the first correction circuit 2 is input to the second correction circuit 3 and the comparators 4, 5, and 6, respectively. One input of the comparators 4, 5, 6 is 255, and if the R'G'B 'signal exceeds 255, the comparators 4, 5, 6 output 1 and R'G'B' If the signal does not exceed 255, comparators 4, 5, and 6 output 0. The outputs of the three comparators 4, 5, and 6 are input to the second correction circuit 3 via the OR circuit 7.
[0024]
FIG. 4 shows the configuration of the second correction circuit. The output of the OR circuit 7 is input to the maximum value circuit 22 for obtaining the maximum value of the R'G'B 'signal, and controls the maximum value circuit 22. That is, when the output of the OR circuit 7 is 1 (when the maximum value exceeds 255), the output M of the maximum value circuit 22 becomes max (R′G′B ′). When the output of the OR circuit 7 is 0 (when the maximum value does not exceed 255), the output M of the maximum value circuit 22 becomes 255. The output of the maximum value circuit 22 is input to the input / output ratio generation circuit 18 to output 255 / M.
[0025]
The multipliers 19, 20, and 21 multiply the R ′, G ′, and B ′ signals by the output signal 255 / M of the input / output ratio generation circuit 18 and output R0, G0 as the output of the second correction circuit 3. , B0 (however, by multiplying R ′, G ′, B ′ by 255 / M, the edge enhancement is slightly weakened). Therefore, R0, G0, and B0 fall within the range of 0 to 255, and the ratio of each color between input and output is R ': G': B '= R0: G0: B0 in the second correction circuit. Therefore, R: G: B = R0: G0: B0, and the ratio of each color becomes equal between input and output.
[0026]
FIG. 5 shows another configuration example of the block 100 in FIG. The maximum value detection circuit 26 outputs max (R′G′B) from R′G′B ′. The comparator 27 compares the output of the maximum value detection circuit 26 with 255, outputs 1 if the output of the maximum value detection circuit 26 is greater than 255, and outputs 1 if the output of the maximum value detection circuit 26 is 255 or less. Outputs 0.
[0027]
The selector 28 selects the output of the maximum value detection circuit 26 when the output of the comparator 27 is 1, outputs M, and selects 255 when the output of the comparator 27 is 0, and outputs 255 as M. I do. The input / output ratio generation circuit 29 receives the output M of the selector 28 and outputs 255 / M. The multipliers 23, 24, and 25 multiply the R ', G', and B 'signals by the output signal 255 / M of the input / output ratio generation circuit 29, and output R0, G0 as an output of the second correction circuit 3. , B0. That is, R ': G': B '= R0: G0: B0 holds. Since R: G: B = R ': G': B 'before and after the first correction circuit 2, R: G: B = R0: G0: B0 holds.
[0028]
FIG. 6 shows the configuration of another embodiment of the present invention. As in the embodiment of FIG. 1, an 8-bit RGB color image signal digitally input from a color scanner or the like is an input signal. The edge emphasis circuit 30 performs edge emphasis on the G signal of the input signals. This circuit is similar to that described in FIG.
[0029]
The arithmetic means 31 receives the RGB signal and the signal Ge after edge enhancement. FIG. 7 shows the configuration of the calculating means 31. The comparator 33 compares the color signal R not subjected to edge enhancement with 0, and as a result of the comparison, outputs 1 if R = 0, and outputs 0 if R ≠ 0. The selector 36 selects 1 when the output of the comparator 33 is 1, and selects and outputs R when the output of the comparator 33 is 0. The arithmetic unit 39 divides a predetermined value (255 in this case because it is 8 bits) by the output R ′ of the selector 36. That is, 255 / R ′ is calculated. The B signal is configured similarly to the R signal, and 255 / B 'is calculated.
[0030]
On the other hand, the edge-enhanced Ge and G are as follows. The comparator 35 compares G and 0, and outputs 1 when G = 0 and outputs 0 when G ≠ 0. The selector 38 selects Ge when the output of the comparator 35 is 1, and selects G when the output of the comparator 35 is 0 to output G ′. The calculator 41 calculates Ge / G ′. The minimum value detector 42 detects the values calculated by the calculators 39, 40, 41, that is, the minimum values of 255 / R ', 255 / B', and Ge / G ', and outputs the value N.
[0031]
Returning to FIG. 6, the correcting unit 32 corrects the RGB signals according to the output N of the calculating unit 31, and outputs R0, G0, and B0. FIG. 8 shows a configuration of the correction unit 32. The multipliers 43, 44, and 45 multiply the RGB signal by the output N of the calculating means 31. The outputs are R0, G0, and B0, respectively.
[0032]
As described above, the correction unit 32 is configured by the multiplier, and one of the values to be multiplied is the same for every color signal, so that R: G: B = R0: G0: B0 is guaranteed. That is, the input color ratio and the output color ratio become equal.
[0033]
In the above embodiment, the edge enhancement circuit is provided for the G signal, but the edge enhancement circuit may be provided for the R and B signals instead of the G signal. Further, this embodiment can be easily applied to CMY or CMYK signals in addition to RGB signals.
[0034]
【The invention's effect】
As described above, according to the present invention, since one edge enhancement circuit is configured, the sharpness of a color image can be corrected with a small-scale circuit configuration and at low cost. Also, the first correction means corrects each color ratio of the input signal and each color ratio of the output signal to be equal, and the second correction means makes the respective color ratios of the input signal and each color ratio of the output signal equal. Since the output signal is kept within the predetermined range while performing the correction, the occurrence of blur of the reproduced color and the shift of the color reproduction is avoided, and the image quality is improved.
[Brief description of the drawings]
FIG. 1 shows a configuration of an embodiment of the present invention.
FIG. 2 shows a configuration of an edge enhancement circuit.
FIG. 3 shows a configuration of a first correction circuit.
FIG. 4 shows a configuration of a second correction circuit.
FIG. 5 shows another configuration example of the block 100 in FIG.
FIG. 6 shows a configuration of another embodiment of the present invention.
FIG. 7 shows a configuration of a calculation unit in another embodiment.
FIG. 8 shows a configuration of a correction unit in another embodiment.
FIG. 9 is a diagram illustrating a color reproduction range of a color output device.
FIGS. 10 (a), (b), and (c) are diagrams illustrating color balance collapse in a conventional method.
FIGS. 11A and 11B show a CCD line sensor of a scanner.
FIGS. 12A and 12B show examples of an edge enhancement mask.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 edge enhancement circuit 2 first correction circuit 3 second correction circuit 4, 5, 6 comparator 7 OR circuit

Claims (4)

Edge enhancement means for performing edge enhancement on at least one color signal of the digital color image signal, and first correction for correcting the digital color image signal based on a signal before edge enhancement and a signal after edge enhancement. Means, a determination means for determining whether or not a signal of at least one color among the corrected signals exceeds a predetermined value, and a second means for correcting the corrected signal according to the determination result. A color image processing apparatus, wherein the first correction means performs correction so that each color ratio of a signal inputted to the first correction means and a signal outputted therefrom becomes equal. . Edge enhancement means for performing edge enhancement on at least one color signal of the digital color image signal, and first correction for correcting the digital color image signal based on a signal before edge enhancement and a signal after edge enhancement. Means, a determination means for determining whether or not a signal of at least one color among the corrected signals exceeds a predetermined value, and a second means for correcting the corrected signal according to the determination result. Correction means, wherein the first correction means comprises: a signal obtained by multiplying each of the other color signals by a value of a ratio between the color signal after the edge enhancement and the color signal before the edge enhancement; A color image processing apparatus for performing correction so as to output a post-color signal and a post-correction signal . Edge enhancement means for performing edge enhancement on at least one color signal of the digital color image signal, and first correction for correcting the digital color image signal based on a signal before edge enhancement and a signal after edge enhancement. Means, a determination means for determining whether or not a signal of at least one color among the corrected signals exceeds a predetermined value, and a second means for correcting the corrected signal according to the determination result. Color image processing , wherein the second correction means performs correction so that the respective color ratios of the signal input to the second correction means and the output signal become equal. apparatus. Edge enhancement means for performing edge enhancement on at least one color signal of the digital color image signal, and first correction for correcting the digital color image signal based on a signal before edge enhancement and a signal after edge enhancement. Means, a determination means for determining whether or not a signal of at least one color among the corrected signals exceeds a predetermined value, and a second means for correcting the corrected signal according to the determination result. Correction means, the second correction means, when the determination means determines that the value exceeds a predetermined value, the value of the ratio of the predetermined value and the maximum value of the signal after the correction Is output so as to output a signal obtained by multiplying the corrected signal by the above-mentioned signal .

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