JPH10191063A - Contour emphasis method and device for color image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a contour emphasis device for color images that never reduces the contour emphasis capability to the fine characters, etc., despite the slight slippage caused among the color components. SOLUTION: The R, G and B signals are inputted for each pixel that is obtained via an image input part of a scanner, etc. A main signal S is produced based on the R and G signals and set at the smaller one (minimum value) of both value of R and G signals. Thus, the large line width the high edge emphasis are secured despite the slight slippage caused among the color components. Then the signals S is smoothed and turned into an unsharp signal U, and an unsharp mask signal (S-U) is obtained. The signal (S-U) is multiplied by an emphasis coefficient P that is obtained from a main correction part 13, and a corrected contour emphasis signal Q is obtained via an edge correction part 15. Then the signal Q is synthesized with each signal obtained from a color conversion part 16 to perform the contour emphasis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for enhancing the outline of a color image obtained from a scanner, a digital camera, or another apparatus.

[0002]

2. Description of the Related Art An image signal obtained when a color original is read by a scanner or the like is represented by R (red), G
(Green) and B (blue). When the contour enhancement of the obtained image is performed, the main signal S is generated based on the R, G, and B signals for the target pixel to be processed, and the contour enhancement signal is generated for the main signal S. Is done.

The main signal S is a gray signal in which each color component signal is mixed. The “gray signal” is a signal in which a plurality of color components are mixed. Conventionally, the main signal S is represented by a mixture ratio of R, G, B of Ar: Ag: Ab.

[0004]

(Equation 1)

[0005] It was determined as follows.

[0006] Then, by performing a smoothing process on the main signal S, an unsharp signal U which is a blur signal is generated. In the smoothing process performed here, a weighted average based on the weighting coefficient between the main signal S for the target pixel and its surrounding pixels, which is the processing target, is used. Then, the difference (S−U) between the main signal S and the unsharp signal U
To obtain an unsharp mask signal and an edge emphasis signal. Finally, by adding the contour emphasis signal and the respective color component signals R, G, B, a contour emphasized signal of the target pixel is generated for each color component.

By performing such processing for all the pixels constituting the image signal, the outline enhancement processing is performed for the entire image.

[0008]

However, in the conventional edge enhancement processing, if the positions of the R, G, and B colors are slightly shifted on the image plane, the edge enhancement of fine characters and the like is weakened. There's a problem.

For example, in a process such as printing, a printed matter is prepared using C (cyan), M (magenta), Y (yellow), and K (black) plates prepared based on the shifted R, G, and B. However, the outline emphasis is similarly weakened, and thin characters tend to be thinner.

In an apparatus such as a scanner for reading a color original by a three-line color sensor system, when the feed speed of the color original is not constant, the R, G, and B color component signals are sent in the feed direction. Will be shifted. In addition, in a scanner or the like, misregistration always occurs in each color component due to chromatic aberration of an optical lens for reading a color original. The misregistration of each of these color components makes a thin character thin or blurs an image.

This phenomenon is attributable to the fact that the main signal S is obtained by the weighted average of the R, G, and B signals as shown in Expression 1 for the target pixel. That is, R, G, B
In some cases, the R signal is a portion indicating an edge of an image or the like, but the B signal is a portion that is not an edge of the image. By taking the weighted average of the non-image portions, the edge strength of the original image is impaired.

For example, if the mixing ratio of R, G, B is Ar: A
The case where g: Ab = 1: 1: 1: 0 will be described. FIG.
FIG. 3 is an explanatory diagram showing conventional edge enhancement. FIG. 8 (a),
Assume that the R signal and the G signal are shifted by one pixel when a color original is read as shown in FIG. This R, G
FIG. 8C shows a case where the main signal S is generated from Equation 1 based on the signal and the mixing ratio. When the main signal S is subjected to a smoothing process, an unsharp signal U as shown in FIG. 8D is generated. Here, the smoothing process is an average of three pixels of the target pixel and its neighboring pixels. Then, the unsharp mask signal (SU) is obtained by subtracting the unsharp signal U from the main signal S (FIG. 8E). By adding this unsharp mask signal (SU) to the R signal, a contour-enhanced signal {R + (SU)} for R is obtained, and the contour-enhanced signal for G is added to the G signal. Signal ｛G + (S-
U) is obtained (FIGS. 8F and 8G).

A comparison between the contour-enhanced signal {R + (SU)} for R and the contour-enhanced signal {G + (SU)} for G shown in FIGS. , R and the line width Wg of G are the same, but their positions are shifted by one pixel. And this one
When an image is displayed (or recorded) based on the edge-enhanced signals of R and G shifted by pixels, only the portions where the signal values of both R and G are low are displayed in black. The portion where the signal value of R is low but the signal value of G is high, or conversely, the portion where the signal value of R is high but the signal value of G is low, is displayed with a blurred image. Although the width of the original line (the width displayed in black) as shown in FIGS. 8A and 8B is equivalent to three pixels, the line width is increased by the conventional edge enhancement processing. (The width displayed in black) is equivalent to two pixels. further,
Although the edges of the original image as shown in FIGS. 8A and 8B are steep, the edges of S have a gentle slope as shown in FIG. 8C. For this reason,
The level h of the (SU) signal shown in FIG. 8E has a value considerably smaller than the original value, and sufficient edge enhancement is not performed.

Therefore, if the position of each of the colors R, G, and B is shifted even by one pixel on the image plane, an effect contrary to the original contour enhancement occurs. This phenomenon is particularly noticeable when displaying (or recording) black characters on a white background.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has been made in consideration of the above-mentioned problems. It is intended to provide the device.

[0016]

According to one aspect of the present invention, there is provided a method for performing edge enhancement based on at least two signal values of a plurality of signal values for different colors. A main signal generating step of generating a main signal from at least two signal values; a blur signal generating step of performing a smoothing process on the main signal to generate a blur signal;
An edge enhancement signal generation step of generating an edge enhancement signal based on the main signal and the blur signal; and a signal synthesis step of synthesizing the edge enhancement signal with each signal value corresponding to each of the plurality of signal values. In the generation step, a minimum value or a maximum value of at least two signal values is selected as a main signal for each pixel.

According to a second aspect of the present invention, in the method according to the first aspect, the main signal generating step includes the step of enhancing at least two signal values for each pixel with respect to contour enhancement of an image element having a signal level lower than that of the surroundings. The minimum value is selected as the main signal.

The third aspect of the present invention is the first or second aspect.
Wherein the plurality of signal values for different colors are three-component signal values for red, green, and blue, and the main signal generation step includes the step of generating at least one of the three component signal values for red and green. The main signal is generated on the basis of the signal value of.

According to a fourth aspect of the present invention, there is provided an apparatus for performing edge enhancement based on at least two signal values of a plurality of signal values for different colors, wherein a main signal is generated from at least two signal values. Main signal generation means, a blur signal generation means for performing a smoothing process on the main signal to generate a blur signal, an outline emphasis signal generation means for generating an outline emphasis signal based on the main signal and the blur signal, Signal synthesizing means for synthesizing an outline emphasis signal with each signal value corresponding to each of the plurality of signal values, wherein the main signal generating means determines a minimum value or a maximum value of at least two signal values for each pixel. Select to be the main signal.

According to a fifth aspect of the present invention, in the apparatus according to the fourth aspect, the main signal generating means is configured to output at least two signal values for each pixel for contour enhancement of an image element whose signal level is lower than that of the surroundings. The minimum value is selected as the main signal.

The invention described in claim 6 is the invention according to claim 4 or 5
Wherein the plurality of signal values for each of the different colors are three-component signal values for red, green, and blue, and the main signal generation means includes at least one of the three-component signal values for red and green. The main signal is generated on the basis of the signal value of.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION

<Overall Configuration of Apparatus> An example of the overall configuration of an apparatus to which an embodiment of the present invention is applied will be described. FIG. 1 is a diagram showing an overall configuration of an apparatus to which an embodiment of the present invention is applied. The image input unit 100 optically reads a color original, such as an input scanner, and generates digital image data for each of R, G, and B colors. Then, the generated image data is transferred to the image processing unit 200. The image data is output to an image output unit 300 such as an output scanner after a predetermined process is performed in the image processing unit 200. In the output scanner 300, C, M, Y, and K are recorded on a recording medium such as a film.
Is recorded for each color. In order to cause the image input unit 100, the image processing unit 200, and the image output unit 300 to perform a desired operation of the operator, the operation input unit 20
1 and an information display unit 202 are provided. Further, the image processing section 200 is provided with an outline emphasis processing section 250, and the embodiment of the present invention is applied.

<Color Image Contour Emphasis Apparatus> Next, a color image contour emphasis apparatus according to an embodiment of the present invention will be described. FIG. 2 is a configuration diagram of a contour emphasizing device showing an embodiment of the present invention. The input of this contour emphasis device is each color component signal for R, G, B.

The R signal and the G signal are converted to the main signal
It is led to. The main signal generator 10 generates a main signal S, which is a gray signal based on the R and G color components, as described later. Then, the obtained main signal S is sent to the unsharp signal generation unit 11, the subtraction unit 12, and the main correction unit 13.

The unsharp signal generation unit 11 obtains the weighted average of the target pixel and its surrounding pixels using a smoothing filter as shown in FIG. 3A, for example. This smoothing filter is shown more generally in FIG.
The result is as shown in FIG. In FIG. 3B,
kij is a weighting coefficient at the position (i, j) and is a positive number. If the position of the pixel of interest is (X, Y), the unsharp signal U is

[0026]

(Equation 2)

[0027] The unsharp signal U obtained here is a signal obtained by a weighted average of the target pixel and its surrounding pixels, and is a so-called blur signal.

Then, the obtained unsharp signal U is sent to the subtraction section 12. Then, the subtraction unit 12 generates an unsharp mask signal (SU) obtained by subtracting the unsharp signal U from the main signal S.

Further, the main correction section 13 outputs the enhancement coefficient P based on a function table stored in a storage medium such as a memory (not shown). FIG. 4 is a diagram showing the relationship between the main signal S and the emphasis coefficient P. The emphasis coefficient P is determined according to the signal level of the main signal S to be input, and
Sent to As shown in FIG. 4, when the level of the main signal S is in the highlight portion and the shadow portion, the noise is easily noticeable, so that the emphasis coefficient P is set to a small value.

The multiplier 14 derives an outline emphasis signal P (SU) which is a product of the emphasis coefficient P and the unsharp mask signal (SU). The contour emphasis signal P (S-
U) has a small value in the highlight portion and the shadow portion of the image, and noise in this portion is suppressed. Then, the obtained contour emphasis signal P (SU) is input to the edge correction unit 15.

In the edge correction section 15, the contour emphasis signal P
The corrected contour emphasis signal Q is output according to the level of (SU). FIG. 5 is a diagram illustrating a relationship between the corrected contour emphasizing signal Q and the contour emphasizing signal P (SU). The relationship in FIG. 5 is stored as a function table in a storage medium such as a memory (not shown), and the input contour enhancement signal P (S
-U), the storage medium is referred to based on the value to obtain a corrected edge enhancement signal Q as an output. In addition, as shown in FIG. 5, the portion where the level of the contour emphasis signal P (SU) is small is corrected to a smaller value in order to suppress the granularity of the image.

Further, R,
Each color component signal for G and B is also guided to the color conversion unit 16. Then, in the color conversion section 16, gradation correction or the like is performed on each of the R, G, and B signals,
Conversion from the B signal to the Y, M, C, and K signals is performed. Therefore, the output of the color conversion unit 16 is the corrected signal R ', when gradation correction is performed on the R, G, B signals.
G ′, B ′, and when RGB is converted to YMCK, they are Y, M, C, K signals. Then, the output is sent to the signal combining unit 17.

The signal synthesizing unit 17 corrects the R ', G', B 'signals or the Y, M, C, K signals sent from the color conversion unit 16 and sends the correction signals sent from the edge correction unit 15 respectively. The edge-enhanced signal Q is multiplied by a different coefficient and added to generate an edge-enhanced signal for each color component signal. Note that this contour enhanced signal becomes Er, Eg, Eb when the corrected contour enhanced signal Q is added to the R ′, G ′, B ′ signals, and when the corrected edge enhanced signal Q is added to the Y, M, C, K signals. Are Ec, Em, Ey, and Ek.

<Details of Main Signal Generation Unit> Next, a method of generating the main signal S, which is a gray signal, from the R and G signals in the main signal generation unit 10 will be described. In the present embodiment, the main signal S is generated from R and G because the B signal contains a large amount of noise components because the roughness of the film is easily picked up when a film original is read by a scanner or the like. This is because it is not suitable for processing. Therefore, if any noise countermeasure processing is performed on the B signal to suppress the noise component, all the R, G, and B signals are input to the main signal generation unit 10 to generate the main signal S. good.

Here, generation of the main signal S based on two signals of the R signal and the G signal will be described. For example,
When displaying a black character or the like on a white background, the minimum value of each of the input R signal and G signal for each pixel is selected as the main signal S. Conversely, when displaying white characters or the like in black, the maximum value of the input R signal and G signal for each pixel is selected as the main signal S. Thus, even when the positions of the R signal and the G signal are slightly shifted by setting the minimum value or the maximum value as the main signal S, the characters are not thinned and the image is not blurred. On the contrary, characters can be made thicker.

In general, when displaying or recording fine characters, a thicker character gives a firmer impression of the characters, and appears to have a higher resolution in appearance.
Further, in the printing process, each of the CMYK plates is misaligned, and the characters tend to be thin. Therefore, it is a preferable result that a character or the like becomes thicker using the minimum value or the maximum value of the R signal and the G signal as the main signal S.

When generating the main signal S, the R signal and the G signal
The selection between the minimum value and the maximum value of the signal is made by the operator selecting from a menu screen displayed on the information display unit 202 and inputting a desired process from the operation input unit 201 before processing. Done by As another method, determine whether the image element is a black image element in a white area or a white image element in a black area, select the minimum value in the former case, and In this case, if the maximum value is selected, both "black characters on a white background" and "white characters on a black character" can be favorably emphasized.

<Signal in Each Part> Next, an example of a signal in each part of this embodiment will be described.

First, the case where the minimum value is selected in the main signal generator 10 will be described. FIG. 6 is an explanatory diagram showing contour emphasis according to the embodiment of the present invention. FIG.
Assume that the R signal and the G signal are shifted by one pixel as shown in FIGS. The line width W of the R signal at this time
r1 and the line width Wg1 of the G signal have a width of three pixels.

When the main signal generator 10 generates the main signal S based on the R signal and the G signal, the result is as shown in FIG. That is, the main signal S selects the minimum value of the R signal and the G signal. Therefore, the shift amount between the R signal and the G signal is one pixel, and the line width W of the R signal and the G signal is
Since r1 and Wg1 are equivalent to three pixels, the line width W of the main signal S
s has a width of four pixels.

Next, in the unsharp signal generation section 11, the main signal S is subjected to a smoothing process so that the unsharp signal U
Is generated as shown in FIG. 6D. Note that the unsharp signal U shown in FIG. 6C is an average of three pixels, that is, the target pixel and its adjacent pixels, for the sake of simplicity. Then, the difference (S−U) between the main signal S and the unsharp signal U is derived by the subtraction unit 12, and an unsharp mask signal (SU) is generated.

Thereafter, the product of the enhancement coefficient P obtained from the main correction unit 13 and the unsharp mask signal (SU) is obtained. Here, for the sake of simplicity, the enhancement coefficient P is set to "1". Suppose there is. It is also assumed that the edge correction section 15 outputs the input signal without any correction. In this way, the corrected edge enhancement signal Q output from the edge correction unit 15 becomes equal to the unsharp mask signal (SU). Further, assuming that no color conversion is performed in the color conversion section 16, the signals input to the signal synthesis section 17 are the unsharp mask signal (SU) and the R, G, B signals. The contour-enhanced signal {R + (SU)} for R output from the signal combining unit 17 is as shown in FIG.
The contour enhanced signal {G + (SU)} for G is shown in FIG.
(G).

When comparing the inclination of the edge of the original image in FIGS. 6A and 6B with the inclination of the edge of S in FIG. 6C, both have the same inclination. Therefore, it can be seen that the edge of the (SU) signal level h in FIG. 6E is very strongly emphasized as compared with the (SU) signal level in FIG. 8E.

Then, comparing FIGS. 6F and 6G, R
And the line width Wg2 for G have the same width, and their positions are also the same. At this time, the line widths Wr2 and Wg2 have a width of four pixels, and are equal to three of the line widths Wr1 and Wg1 before edge enhancement.
It is larger than the number of pixels. However, thickening characters and the like as described above is a favorable result,
There is no problem at all. The contour-enhanced signals {R + (SU)} and {G + (SU)} for such R and G.
Since the positions of the finally obtained edges are the same, the image is not blurred even if display or recording is performed based on this signal. Further, when the method of selecting the minimum value is performed as described above, even if a slight shift occurs for each color component,
In particular, black characters and the like can be displayed (or recorded) satisfactorily on a white background.

Next, a case where the main signal generator 10 selects the maximum value will be described. FIG. 7 is an explanatory diagram showing outline emphasis according to the embodiment of the present invention. FIG.
Assume that the R signal and the G signal are shifted by one pixel as shown in FIGS. The line width W of the R signal at this time
r1 and the line width Wg1 of the G signal have a width of three pixels.

When the main signal generator 10 generates the main signal S based on the R signal and the G signal, the result is as shown in FIG. That is, the main signal S selects the maximum value of the R signal and the G signal. Therefore, the shift amount between the R signal and the G signal is one pixel, and the line width W of the R signal and the G signal is
Since r1 and Wg1 are equivalent to three pixels, the line width W of the main signal S
s has a width of four pixels.

Then, similarly to the above case, an unsharp signal U is obtained, and an edge-enhanced signal is obtained. Then, the contour-enhanced signal {R + (SU)} for R output from the signal combining unit 17 is as shown in FIG.
The contour enhanced signal {G + (SU)} for G is shown in FIG.
(G).

When comparing the inclination of the edge of the original image in FIGS. 7A and 7B with the inclination of the edge of S in FIG. 7C, both have the same inclination. For this reason, it can be seen that the edge of the (SU) signal level h in FIG. 7E is very strongly emphasized as compared with the (SU) signal level in FIG. 8E.

7 (f) and 7 (g), R
And the line width Wg2 for G have the same width, and their positions are also the same. At this time, the line widths Wr2 and Wg2 have a width of four pixels, and are equal to three of the line widths Wr1 and Wg1 before edge enhancement.
It is larger than the number of pixels. This is a favorable result as described above, and there is no problem at all. The contour-enhanced signal ｛R + (S−
Since U)｝ and {G + (SU)} have the same edge positions finally obtained, the image will not be blurred even when displayed or recorded based on this signal. In addition, when the method of selecting the minimum value is performed as described above, white characters and the like can be displayed (or recorded) satisfactorily particularly on a black background even if a slight shift occurs for each color component.

<Modification> If the noise component of the B signal has already been suppressed, all the R, G, and B signals may be input to the main signal generator 10 to generate the main signal S. However, in this case as well, by selecting the minimum value or the maximum value from among the R, G, and B signals, it is possible to satisfactorily enhance the outline without thinning or blurring thin characters.

Also, the input of the color image contour enhancing device shown in this embodiment is not a color component signal for R, G, B, but a color component signal for C, M, Y, K. Is also good. Also in this case, when generating the main signal S,
By selecting the minimum value or the maximum value from the C, M, Y, and K signals, thin characters and the like are also favorably emphasized.

[0052]

As described above, according to the first and fourth aspects of the present invention, in generating a main signal, a minimum value or a maximum value of at least two signal values is selected for each pixel. Since the main signal is used as the main signal, even if a slight shift occurs for each color component, it is possible to favorably emphasize the outline without thinning or blurring a thin character.

According to the second and fifth aspects of the present invention, for the edge enhancement of an image element whose signal level is lower than that of the surroundings, the minimum value among at least two signal values is selected for each pixel and used as a main signal. Therefore, even if there is a slight shift for each color component, it is possible to display (or record) satisfactorily without particularly thinning or blurring black characters on a white background.

According to the third and sixth aspects of the present invention, the main signal generating step generates the main signal based on at least the signal values of red and green among the three component signal values. There is no influence of the signal value for a large number of blue, and the contour can be favorably enhanced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of an apparatus to which an embodiment of the present invention is applied.

FIG. 2 is a configuration diagram of a contour emphasizing device showing an embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of a smoothing filter used in an unsharp signal generation unit.

FIG. 4 is a diagram illustrating a relationship between an emphasis coefficient and a main signal.

FIG. 5 is a diagram showing a relationship between a contour enhancement signal and a corrected contour enhancement signal.

FIG. 6 is an explanatory diagram showing contour emphasis according to the embodiment of the present invention;

FIG. 7 is an explanatory diagram showing contour emphasis according to the embodiment of the present invention;

FIG. 8 is an explanatory diagram showing conventional edge enhancement.

[Explanation of symbols]

 Reference Signs List 10 Main signal generation unit 11 Unsharp signal generation unit 12 Subtraction unit 13 Main correction unit 14 Multiplication unit 15 Edge correction unit 16 Color conversion unit 17 Signal synthesis unit 100 Image input unit 200 Image processing unit 300 Image output unit S Main signal U An Sharp signal

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04N 9/68 103 H04N 1/46 Z

Claims (6)

[Claims] 1. A method for performing edge enhancement based on at least two signal values of a plurality of signal values for different colors, comprising: a main signal generating step of generating a main signal from the at least two signal values; A blur signal generation step of performing a smoothing process on the main signal to generate a blur signal, an outline emphasis signal generation step of generating an outline emphasis signal based on the main signal and the blur signal, A signal synthesizing step of synthesizing the contour emphasizing signal with each signal value corresponding to each of the signal values, wherein the main signal generating step comprises:
A method for enhancing a contour of a color image, wherein a minimum value or a maximum value of two signal values is selected as the main signal. 2. The method according to claim 1, wherein, in the main signal generating step, a minimum value of the at least two signal values is selected for each pixel for contour enhancement of an image element having a lower signal level than surroundings. Wherein the main signal is used as the main signal. 3. The method according to claim 1, wherein the plurality of signal values for each different color are three-component signal values for red, green, and blue, and the main signal generating step includes: A method of enhancing a contour of a color image, comprising: generating the main signal based on at least signal values of red and green among the three component signal values. 4. An apparatus for performing edge enhancement based on at least two signal values of a plurality of signal values for different colors, wherein main signal generation means for generating a main signal from the at least two signal values; Blur signal generation means for performing a smoothing process on the main signal to generate a blur signal; contour enhancement signal generation means for generating a contour enhancement signal based on the main signal and the blur signal; Signal synthesizing means for synthesizing the contour emphasizing signal with each signal value corresponding to each of the signal values, wherein the main signal generating means comprises:
An edge enhancement device for a color image, wherein a minimum value or a maximum value among two signal values is selected as the main signal. 5. The apparatus according to claim 4, wherein the main signal generation unit selects a minimum value of the at least two signal values for each pixel for contour enhancement of an image element whose signal level is lower than that of the surroundings. A color signal edge enhancement device for obtaining a main signal. 6. The apparatus according to claim 4, wherein the plurality of signal values for each of the different colors are three-component signal values for red, green, and blue. An edge enhancement device for a color image, wherein the main signal is generated based on at least signal values of red and green among the three component signal values.