JP5933332B2 - Image processing apparatus, image processing method, image processing program, and recording medium storing image processing program - Google Patents

Description

  The present invention relates to an image processing apparatus, for example, an image processing apparatus that performs edge enhancement processing, an image processing method, an image processing program, and a recording medium storing the image processing program.

  Conventionally, an edge enhancement process, which is an image process for enhancing an edge of an input image, is known. Techniques relating to such edge enhancement processing are described in Patent Documents 1 and 2, for example.

  In the conventional edge enhancement processing described in Patent Documents 1 and 2, for an input image indicated by a luminance signal and a color difference signal, only the luminance signal is corrected, and the color difference signal is not corrected. . For this reason, before and after the edge enhancement process, only the luminance changes and the color difference remains unchanged. As a result, the ratio between the luminance and the color difference changes before and after the edge enhancement processing. As a result, for example, when the luminance is increased by the edge enhancement process, the color difference is relatively decreased with respect to the luminance, thereby causing fading.

  In relation to the present invention, Patent Document 3 discloses an image display device that performs brightness control and color gain control on a luminance signal and a color difference signal, respectively. In color gain control, the color difference is corrected with a color gain amount corresponding to the average luminance of the input image obtained by brightness control. According to this image display device, both luminance and color difference can be changed.

JP 2008-92462 A JP 2001-245158 A JP 2006-285063 A

  However, in the image display device described in Patent Document 3, the color difference is corrected with a uniform color gain amount for all the pixels using the average luminance of the input image. For this reason, in the case of performing luminance correction that may cause a different luminance change for each pixel of the input image, the ratio between the luminance and the color difference is not maintained before and after the correction. Thereby, it becomes difficult to suppress the above-mentioned fading.

  Therefore, the present invention provides an image processing apparatus, an image processing method, an image processing program, and a recording medium storing the image processing program that suppress fading that may occur when performing luminance correction such as edge enhancement processing. Objective.

A first aspect of the present invention is an image processing apparatus that corrects an input image,
An image processing apparatus for correcting an input image,
A luminance correction unit that performs correction for enhancing the edge of the input image with respect to the luminance signal indicating the input image ;
A coefficient acquisition unit that acquires a first coefficient that is a ratio of the luminance signal after correction to the luminance signal before correction;
A color correction unit that corrects a signal indicating the color of the input image based on the first coefficient ;
The brightness correction unit
A plurality of filters receiving the luminance signal and having different frequency characteristics from each other;
It is obtained by adding the output code of the filter having the lowest passband frequency among the plurality of filters to the value obtained by multiplying the absolute value obtained based on the outputs of the plurality of filters by the second coefficient. And a correction processing unit that adds a correction amount to the luminance signal .

According to a second aspect of the present invention, in the first aspect of the present invention,
The color correction unit corrects a color difference signal indicating the input image based on the first coefficient.

According to a third aspect of the present invention, in the second aspect of the present invention,
The color correction unit may multiply the color difference signal by the first coefficient.

According to a fourth aspect of the present invention, in the second aspect of the present invention,
The color correction unit includes a coefficient adjustment unit that adjusts the first coefficient acquired by the coefficient acquisition unit, and multiplies the color difference signal by the adjusted first coefficient.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention,
The coefficient adjustment unit sets the first coefficient to 1 when the first coefficient acquired by the coefficient acquisition unit is smaller than 1.

According to a sixth aspect of the present invention, in the first aspect of the present invention,
A primary color conversion unit that converts a luminance signal and a color difference signal before correction indicating the input image into a primary color signal;
The color correction unit corrects the primary color signal obtained by the primary color conversion unit based on the first coefficient.

According to a seventh aspect of the present invention, in the first aspect of the present invention,
The absolute value is a sum of absolute values of outputs of the filters.

According to an eighth aspect of the present invention, in any one of the first to sixth aspects of the present invention,
The input image is indicated by a luminance signal and a color difference signal.

A ninth aspect of the present invention is the eighth aspect of the present invention,
The image processing apparatus further includes a luminance / color difference conversion unit that converts a primary color signal indicating the input image into a luminance signal and a color difference signal indicating the input image.

A tenth aspect of the present invention is an image processing method for correcting an input image,
A luminance correction step for performing correction for emphasizing an edge of the input image with respect to the luminance signal indicating the input image ;
A coefficient acquisition step of acquiring a first coefficient that is a ratio of the luminance signal after correction to the luminance signal before correction;
A color correction step of correcting a signal indicating the color of the input image based on the first coefficient ,
The brightness correction step includes
Providing the luminance signal to a plurality of filters having different frequency characteristics;
It is obtained by adding the output code of the filter having the lowest passband frequency among the plurality of filters to the value obtained by multiplying the absolute value obtained based on the outputs of the plurality of filters by the second coefficient. And a correction processing step of adding a correction amount to the luminance signal .

An eleventh aspect of the present invention is an image processing program for correcting an input image,
A luminance correction step for performing correction for emphasizing an edge of the input image with respect to the luminance signal indicating the input image ;
A coefficient acquisition step of acquiring a first coefficient that is a ratio of the luminance signal after correction to the luminance signal before correction;
Causing the computer to execute a color correction step of correcting a signal indicating the color of the input image based on the first coefficient ;
The brightness correction step includes
Providing the luminance signal to a plurality of filters having different frequency characteristics;
It is obtained by adding the output code of the filter having the lowest passband frequency among the plurality of filters to the value obtained by multiplying the absolute value obtained based on the outputs of the plurality of filters by the second coefficient. And a correction processing step of adding a correction amount to the luminance signal .

A twelfth aspect of the present invention is a computer-readable recording medium,
An image processing program according to an eleventh aspect of the present invention is recorded.

According to the first aspect of the present invention, since the color is corrected based on the first coefficient, the color change is determined according to the luminance change by the luminance correction that emphasizes the edge of the input image . For this reason, the ratio between the luminance after luminance correction and the color difference can be adjusted. For example, when the luminance is increased by luminance correction that emphasizes the edge of the input image, the ratio between the luminance and the color difference is maintained before and after the luminance correction by making the color proportional to the luminance based on the first coefficient. As a result, it is possible to suppress fading that may occur due to a relatively small color difference with respect to luminance.
Further, according to the first aspect of the present invention, since the correction amount is generated, a value obtained by multiplying the absolute value obtained based on outputs of a plurality of filters having different frequency characteristics from each other by the second coefficient is used. A correction amount is obtained by averaging the outputs of a plurality of filters having different frequency characteristics. In addition, since the code of the output of the filter having the lowest passband frequency among the plurality of filters is used as the correction amount code, all input images except for the input image with extremely small luminance change (very low frequency). The sign of the correction amount is appropriately set according to the sign of the output of the filter having the lowest frequency characteristic from which the output result is obtained. For example, for an input image including a relatively thick (gradual) edge, a value obtained by averaging the outputs of a plurality of filters having different frequency characteristics acts in a direction to appropriately emphasize the edge. On the other hand, for input images that contain noise, the code of the output of the filter having the lowest frequency in the passband, which is a code that acts in the direction of suppressing noise, is used as the correction amount code, so that the frequency of each other A value obtained by averaging the outputs of a plurality of filters having different characteristics acts in a direction to suppress noise. In this way, it is possible to emphasize a relatively thick edge while suppressing noise.

  According to the second aspect of the present invention, since the color difference signal is corrected based on the first coefficient, the color difference change is determined according to the luminance change by the luminance correction. In this way, the same effects as those of the first aspect of the present invention can be achieved.

  According to the third aspect of the present invention, the color difference changes in proportion to the luminance by multiplying the color difference signal by the first coefficient. For this reason, when the luminance is increased by the luminance correction, the ratio between the luminance and the color difference is maintained before and after the luminance correction, so that fading can be suppressed. In addition, even when the brightness is reduced by brightness correction, the ratio between brightness and color difference is maintained before and after brightness correction, so the color is unnaturally bright due to the relatively large color difference with respect to brightness. Can be prevented.

  According to the fourth aspect of the present invention, the degree of color difference correction is changed as necessary by adjusting the first coefficient. For this reason, it is possible to obtain images with saturation according to various applications.

  According to the fifth aspect of the present invention, the color difference does not change when the luminance is reduced by the luminance correction. For this reason, a vivid image in which only fading is suppressed can be obtained.

  According to the sixth aspect of the present invention, since the primary color signal is corrected based on the first coefficient, the primary color change is determined according to the luminance change due to the luminance correction. When considering the primary color signal after the correction by the color correction unit from the viewpoint of the luminance signal and the color difference signal, the primary color change is determined according to the luminance change due to the luminance correction, so that the ratio between the luminance and the color difference after the luminance correction is determined. Can be adjusted. In this way, the same effects as those of the first aspect of the present invention can be achieved.

According to the seventh aspect of the present invention, the filter having the lowest passband frequency among the plurality of filters is obtained by multiplying the sum of the absolute values of the outputs of the plurality of filters having different frequency characteristics by a predetermined coefficient. The amount of correction can be obtained by adding the output sign. That is, the correction amount is a value obtained by adding the sign of the output of the filter having the lowest passband frequency to the value averaged without canceling the outputs of the plurality of filters. For this reason, for example, for an input image including noise, the averaged value without canceling out the outputs of the plurality of filters acts in a direction to suppress noise. Thereby, noise can be further suppressed.

According to the eighth aspect of the present invention, for example, by correcting an input image indicated by an image signal obtained by receiving a television broadcast or obtained from a video system, the first to sixth aspects of the present invention The same effect as any one up to the aspect can be achieved.

According to the ninth aspect of the present invention, for example, the input image indicated by the image signal received from the multimedia system is corrected, and the same effect as any of the first to sixth aspects of the present invention is achieved. be able to.

According to the tenth aspect of the present invention, in the image processing method, the same effect as in the first aspect of the present invention can be achieved.

According to the eleventh aspect of the present invention, the image processing program can achieve the same effects as those of the first aspect of the present invention.

According to the twelfth aspect of the present invention, the same effects as those of the first aspect of the present invention can be achieved in a computer-readable recording medium.

It is a block diagram which shows the hardware constitutions of the image processing apparatus which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the functional structure of the principal part of the image processing apparatus which concerns on the said 1st Embodiment. It is a block diagram which shows the functional structure of the edge emphasis part in the said 1st Embodiment. It is a figure which shows the frequency characteristic of the 1st-3rd filter in the said 1st Embodiment. In the said 1st Embodiment, it is a schematic diagram for demonstrating a mode that an edge is emphasized by the 3rd filter. More specifically, (a) is a schematic diagram showing a luminance signal before processing, (b) is a schematic diagram showing an output of the third filter, and (c) is a process in which the output of the third filter is added. It is a schematic diagram which shows a front luminance signal. It is a schematic diagram which shows the output of the 1st-3rd filter with respect to the comparatively thick edge in the said 1st Embodiment. More specifically, (a) is a schematic diagram showing a luminance signal before processing, (b) is a schematic diagram showing an output of the first filter, and (c) is a schematic diagram showing an output of the second filter. (D) is a schematic diagram showing the output of the third filter. It is a schematic diagram which shows the output of the 1st-3rd filter with respect to the noise in the said 1st Embodiment. More specifically, (a) is a schematic diagram showing a luminance signal before processing, (b) is a schematic diagram showing an output of the first filter, and (c) is a schematic diagram showing an output of the second filter. (D) is a schematic diagram showing the output of the third filter. Is a diagram illustrating a C _b C _r coordinates. It is a block diagram which shows the functional structure of the principal part of the image processing apparatus which concerns on the 2nd Embodiment of this invention. It is a block diagram which shows the functional structure of the principal part of the image processing apparatus which concerns on the 3rd Embodiment of this invention. It is a block diagram which shows the functional structure of the principal part of the image processing apparatus which concerns on the 4th Embodiment of this invention.

  Hereinafter, first to third embodiments of the present invention will be described with reference to the accompanying drawings.

<1. First Embodiment>
<1.1 Configuration and processing overview>
FIG. 1 is a block diagram illustrating a hardware configuration of the image processing apparatus according to the present embodiment. As shown in FIG. 1, the image processing apparatus includes a CPU 1, an input unit 2, a memory 3, a hard disk device 4, and an output unit 5. The hard disk device 4 stores an image processing program 6 for causing the CPU 1 to execute image processing in the present embodiment. For example, the image processing program 6 may be read and installed by a DVD drive (not shown) from a computer-readable recording medium such as a DVD-ROM storing the image processing program 6 or via a network (not shown). May be supplied and installed.

  The image processing apparatus receives an input image signal IN from the outside via the input unit 2. The input image signal IN indicates an input image. The memory 3 temporarily stores the input image signal IN and the image processing program 6 read from the hard disk device 4, and the CPU 1 corrects the input image based on the image processing program 6. In the present embodiment, the correction performed on the input image is luminance correction and color difference correction. An output image signal OUT indicating an output image obtained by correcting the input image is output to the outside via the output unit 5.

FIG. 2 is a block diagram illustrating a functional configuration of a main part of the image processing apparatus according to the present embodiment. As shown in FIG. 2, the image processing apparatus, the edge enhancement unit 10 as the luminance correction unit, the coefficient obtaining unit 20, YC _b C _r -RGB as a color difference correction unit 30, and the primary conversion of the color correction unit A conversion unit 40 is provided. Edge enhancement unit 10, the respective coefficient acquisition unit 20, the color difference correction unit 30 and the YC _b C _r-RGB conversion unit 40, and is implemented by software by CPU 1. Incidentally, the edge enhancement unit 10, the coefficient obtaining unit 20, the color difference correction unit 30, and YC _b C _r each -RGB converter 40 may be hardware implemented.

This image processing apparatus corrects an input image indicated by an input image signal obtained by receiving a television broadcast or obtained from a video system. Therefore, the input image signal IN is composed of a luminance signal Y, first color difference signal C _b, and the second color difference signal C _r. Here, the first color difference signal C _b, representing the difference between the blue component and the luminance signal Y in the input image. The second color difference signal C _r, representing the difference between the red component and the luminance signal Y in the input image.

Edge enhancement unit 10 performs the edge enhancement processing on the luminance signal Y input to the image processing apparatus, providing the luminance signal Y1 after the edge enhancement processing to the coefficient acquisition unit 20 and the YC _b C _r-RGB converter 40. Hereinafter, the luminance signal Y before edge enhancement processing by the edge enhancement unit 10 is referred to as “pre-processing luminance signal”, and the luminance signal Y1 after edge enhancement processing by the edge enhancement unit 10 is referred to as “post-processing luminance signal”. That's it.

The coefficient acquisition unit 20 receives the post-processing luminance signal Y1 that is the output of the edge enhancement unit 10 and the pre-processing luminance signal Y that is the input, and acquires the first coefficient α given by the following equation (1).
α = Y1 / Y (1)
The first coefficient α represents the ratio of the post-processing luminance signal Y1 to the pre-processing luminance signal Y, that is, the luminance change rate due to edge enhancement processing. The coefficient acquisition unit 20 gives the acquired first coefficient α to the color difference correction unit 30.

The color difference correction unit 30 includes first and second color difference correction multiplication units 31 and 32. The color difference correction unit 30 corrects the first and second color difference signals C _b and _Cr using the first coefficient α received from the coefficient acquisition unit 20.

The first color difference correction multiplier unit 31 corrects the first color difference signal C _b. More specifically, the first color difference correction multiplier 31 corrects the first color difference signal C _b to the first color difference signal C _b 1 given by the following equation (2).
C _b 1 = α · C _b (2)
Hereinafter, the first color difference signal C _b before correction by the first color difference correction multiplication unit 31 is referred to as “first color difference signal before correction”, and the first color difference signal C _b 1 after correction is referred to as “correction”. This is referred to as a “first color difference signal”. The first color difference correction multiplication unit 31 provides the corrected first color difference signal C _b 1 to the YC _b C _r -RGB conversion unit 40.

The second color difference correction multiplication unit 32 corrects the second color difference signal _Cr . More specifically, the second color difference correction multiplication unit 32 corrects the second color difference signal C _r to a second color difference signal C _r 1 given by the following equation (3).
C _r 1 = α · C _r (3)
Hereinafter, the second color difference signal C _r before correction by the second color difference correction multiplication unit 32 is referred to as "uncorrected second color difference signal", "correction to a corrected second color difference after signal C _r 1 This is referred to as a “second color difference signal”. The second color difference correction multiplication unit 32 provides the corrected second color difference signal C _r 1 to the YC _b C _r -RGB conversion unit 40.

なお、式（４）におけるＹ，Ｃ_b，Ｃ_rはそれぞれ、処理後輝度信号Ｙ１、補正後第１色差信号Ｃ_b１、および補正後第２色差信号Ｃ_r１に相当する。 The YC _b C _r -RGB converter 40 receives the luminance signal Y1 and the corrected first and second color difference signals C _b 1 and C _r 1 and receives them as a red signal R which is a primary color signal indicating an R (red) component. , B (blue) component blue color signal B, and G (green) component primary color signal green signal G. The YC _b C _r -RGB conversion unit 40 gives an output image signal composed of a red signal R, a blue signal B, and a green signal G to the output unit 5. Here, the signal conversion in YC _b C _r-RGB conversion unit 40 is performed based on the following equation (4).

Incidentally, Y in the formula (4), C _b, are C _r respectively, processed luminance signal Y1, first color difference signal C _b 1 corrected, and correspond to the second color difference signal C _r 1 after the correction.

<1.2 Edge Enhancement Processing Unit>
FIG. 3 is a block diagram illustrating a functional configuration of the edge enhancement unit 10 in the present embodiment. As shown in FIG. 3, the edge enhancement unit 10 includes a plurality (three in the present embodiment) of filters 100a to 100c, a plurality (three in the present embodiment) of absolute value processing units 101a to 101c, and a first addition unit. 102, a first luminance correction multiplication unit 103, a code acquisition unit 104, a second luminance correction multiplication unit 105, and a second addition unit 106.

The three filters 100a to 100c are sharpening filters for performing edge enhancement processing, and output correction amounts for enhancing luminance changes of the input image. A pre-processing luminance signal Y is given to each of the three filters 100a to 100c. Here, representing the three outputs of the filter 100a~100c each code y ₁ ~y _3. The three filters 100a to 100c have different frequency characteristics, and the three filters 100a to 100c are hereinafter referred to as “first to third filters”, respectively. The frequency characteristics of the first to third filters 100a to 100c are as indicated by symbols F1 to F3 in FIG. That is, the first filter 100a is a high-pass filter, the second filter 100b is a bandpass filter having a lower passband frequency (more specifically, a low-frequency cutoff frequency) than the first filter 100a, and the third filter 100c is the second filter 100c. The band-pass filter has a lower passband frequency (more specifically, a lower cut-off frequency). That is, the passband frequency of the third filter 100c is the lowest among the first to third filters 100a to 100c. Hereinafter, the low frequency in the passband may be expressed as “low frequency characteristics”. Similarly, a high frequency in the passband may be expressed as “high frequency characteristics”.

  Note that the normalized frequency in FIG. 4 is normalized by the Nyquist frequency of the pre-process luminance signal Yx. The first to third filters 100a to 100c are realized by, for example, FIR filters. When the FIR filter is used, the number of taps is an odd number. Since the number of taps and the number of parameters in the FIR filter for realizing the first to third filters 100a to 100c are obvious to those skilled in the art, specific numerical values are not illustrated here.

Three absolute value processing unit 101a~101c respectively outputs the absolute value of the output y ₁ ~y ₃ of the first to third filter 100a-100c. Hereinafter, the three absolute value processing units 101a to 101c are referred to as “first to third absolute value processing units”, respectively.

First adder 102 receives the absolute value of the output y ₁ ~y ₃ of the first to third filter 100a-100c, and outputs the output y ₄ obtained by the following equation (5).
y ₄ = | y ₁ | + | y ₂ | + | y ₃ | (5)

The first luminance correction multiplying unit 103 receives the output y ₄ and the second coefficient k of the first adding unit 102, and outputs an output y ₅ obtained by the following equation (6).
y ₅ = k × y ₄ (6)
Here, the second coefficient k is for determining the degree of correction amount in the edge enhancement processing, and is set to 1/3, for example. The second coefficient k, y ₅ is becomes the average of the absolute value of the output y ₁ ~y ₃ of the first to third filter 100a-100c.

Code acquiring unit 104 receives the output y ₃ of the first to the lowest frequency characteristic in the third filter 100a~100c third filter 100c, and outputs a code of the output y ₃ as the output y _6. Specifically, the output y ₆ is acquired by the following equation (7).
y ₆ = sign (y ₃ ) (7)
That is, if positive output y ₃ y ₆ becomes 1, if positive output y ₃ y ₆ becomes -1, (if there is no output) Output y ₃ is if 0 y ₆ is 0.

Second luminance correction multiplication unit 105 receives the output y ₆ output y ₅ and the code acquiring section 104 of the first luminance correction multiplication unit 103, and outputs the output y ₇ obtained by the following equation (8).
y ₇ = y ₆ × y ₅ (8)
In this embodiment, the output y ₇ is the correction amount. Therefore, hereinafter, the output y ₇ is also referred to as “correction amount”.

The second adder 106 receives the pre-process luminance signal Y and the output y ₇ of the second luminance correction multiplier 105, and outputs a post-process luminance signal Y1 obtained by the following equation (9).
Y1 = Y + y ₇ (9)

  The post-process luminance signal Y2 is generated by performing the above process on each pixel of the input image. In the present embodiment, the first to third absolute value processing units 101a to 101c, the first addition unit 102, the first luminance correction multiplication unit 103, the code acquisition unit 104, the second luminance correction multiplication unit 105, and the second A correction processing unit is realized by the adding unit 106.

Here, the function of the filter in the present embodiment will be further described. In FIG. 5, when it is assumed that the edge enhancement process is performed on the pre-process luminance signal Y using only the third filter 100c among the first to third filters 100a to 100c, the edge is enhanced by the third filter 100. It is a schematic diagram for demonstrating a mode performed. More specifically, FIG. 5A is a schematic diagram showing the pre-processing luminance signal Y, FIG. 5B is a schematic diagram showing the output y ₃ of the third filter 100c, and FIG. preprocessing the output y ₃ of the third filter 100c is added is a schematic diagram showing a luminance signal Y. In the figure, the horizontal axis indicates the pixel position, and the vertical axis indicates the luminance. Here, the pixel position in the figure may be either a horizontal position or a vertical position of the image. Further, a pixel position where the luminance change is most caused in the pre-processing luminance signal Y shown in FIG. Hereinafter, the pixel position indicated by the symbol ED is referred to as “position ED”.

As shown in FIG. 5B, the output y ₃ of the third filter 100c has a positive value on the high brightness side (hereinafter also referred to as “bright side”) across the position ED, and the position ED is sandwiched therebetween. Negative value on the low luminance side (hereinafter also referred to as “dark side”). More specifically, the output y ₃ of the third filter 100c, which is a bandpass filter, is obtained by inverting the sign of the secondary differential value obtained based on the frequency characteristic of the sign F3 in FIG. By adding such output y ₃ to the pre-processing luminance signal Y, as shown in FIG. 5C, the luminance change in the vicinity of the position ED is enhanced, and as a result, the edge is enhanced. The output y ₁ of the first filter 100a is obtained by reversing the sign of the secondary differential value obtained based on the frequency characteristic of the sign F1 in FIG. Similarly, the output y ₂ of the second filter 100b is obtained by reversing the sign of the secondary differential value obtained based on the frequency characteristic of the sign F2 in FIG. Since the functions of the first filter 100a and the second filter 100b are the same as those of the third filter 100c except for the frequency characteristics, description thereof is omitted.

Next, in the present embodiment, the first to third filters 100a to 100c having different frequency characteristics are used, and the output y ₄ that is the sum of the absolute values of the outputs and the third filter 100c having the lowest frequency characteristics are used. Regarding the advantage of using the output y ₆ that is the sign of the output y _3, an example in which a relatively thick edge (also referred to as an edge having a relatively slow change in luminance) is included in the input image, and a steep typified by noise. An example will be described in which an edge is included in an input image.

6, in this embodiment, is a schematic diagram showing an output y ₁ ~y ₃ of the first to third filter 100a~100c for relatively thick edge. More specifically, FIG. 6A is a schematic diagram showing the pre-processing luminance signal Y, FIG. 6B is a schematic diagram showing the output y ₁ of the first filter, and FIG. FIG. 6D is a schematic diagram showing the output y _{2 of the} second filter, and FIG. 6D is a schematic diagram showing the output y ₃ of the third filter. The frequency component of the pre-process luminance signal Y shown in FIG. 6A is assumed to be included in the range indicated by the symbol EXA in FIG. 4 with the frequency at the peak of the pass band of the third filter 100c as the upper limit. That is, it is assumed that the luminance change corresponding to the frequency at the peak of the pass band of the third filter 100c occurs in the vicinity of the position ED in the pre-processing luminance signal Y shown in FIG.

As shown in FIG. 6D, the third filter 100c acts to emphasize the luminance change near the position ED most greatly among the first to third filters 100a to 100c. Therefore, the third filter 100c becomes a large positive value at the bright side across the position ED, obtain an output y ₃ become large negative value at the dark side across the position ED. In this way, the third filter 100c obtains an output y ₃ that most emphasizes the luminance change in the vicinity of the position ED among the first to third filters 100a to 100c.

Further, as shown in FIG. 6C, the second filter 100b acts to slightly emphasize the luminance change in the vicinity of the position ED. Therefore, the second filter 100b becomes small positive value at the bright side across the position ED, obtain an output y ₂ comprising a luminance of the dark side across the position ED to a small negative value. In this way, the second filter 100b obtains an output y ₂ that slightly enhances the luminance change near the position ED.

On the other hand, as shown in FIG. 6B, the first filter 100a emphasizes the luminance change in the vicinity of the position ED because the range indicated by the symbol EXA is not included in the passband (see FIG. 4). Does not work. Therefore, the output y ₁ of the first filter 100a is zero.

For example, consider a case where the edge enhancement processing of an input image including a relatively thick edge shown in FIG. 6A is performed using only the output y ₃ of the third filter 100c. In this case, as can be seen from FIG. 6D, the luminance correction is performed in a relatively wide range with the position ED interposed therebetween. If, on the other hand, an use of only the output y ₂ of the second filter 100b, sandwiching the position ED, so that the luminance correction is performed in a narrower range than when using only the output y ₃ of the third filter 100c. The output y ₃ of the first filter 100a is 0 in this example, but only the output y ₁ of the first filter 100a when the input image contains a frequency component slightly higher than this example. Is used, luminance correction is performed in a narrower range than when only the output y ₂ of the second filter 100c is used with the position ED interposed therebetween. As described above, when a single filter is used, there is a possibility that edge enhancement may be excessive due to luminance correction performed in a relatively wide range across the position ED, or edge enhancement may be insufficient or not performed. is there.

In contrast, in the present embodiment, when generating the correction amount y _7, multiplied by a coefficient k to an output y ₄ is the sum of the absolute value of the output y ₁ ~y ₃ of the first to third filter 100a~100c because of the use of the output y _5, the correction amount y ₇ averaged without offsetting the output y ₁ ~y ₃ of the first to third filter 100a~100c is obtained. Further, since the sign of the output y ₃ of the third filter 100c having the lowest frequency characteristic among the first to third filters 100a to 100c is used as the sign of the correction amount y ₇ , the luminance change is extremely small (the frequency change). The sign of the correction amount y ₇ is appropriately set according to the sign of the output y ₃ of the third filter 100 c from which the output result is obtained in all input images except the input image (which is extremely small). In such a setting, for the relatively thick input image edge is included, as described above, a value obtained by averaging the output y ₁ ~y ₃ of the first to third filter 100a-100c (the output y ₅ ) acts in a direction to properly emphasize the edge.

If the sign of the output y ₁ of the first filter 100a having the highest frequency characteristic is used as the sign of the correction amount y ₇ , the sign cannot be obtained in an example in which a relatively thick edge is included in the input image ( That is, the output y ₆ becomes 0). Therefore, in the position to correct the luminance by the correction amount y ₇ averaged without offsetting the output y ₁ ~y ₃ of the first to third filter 100a-100c, the output y ₂ of the second filter 100b and the Even if the output y ₃ of the three filters 100c is present, the correction amount y ₇ becomes 0, so that the correction is not performed. Instead of the edge shown in FIG. 6 (a), when containing the thicker edge than the edge, cause similar problems when using the sign of the second filter 100b as the sign of the correction amount y ₇ obtain.

On the other hand, in the present embodiment, the sign of the output y ₃ of the third filter 100c having the lowest frequency characteristic is used as the sign of the correction amount y ₇ . In an example in which a relatively thick edge is included in the input image, as can be seen from FIG. 6D, the output y ₃ of the third filter 100c exists in a relatively wide range across the position ED. Therefore, by using the sign of the output y ₃ of the third filter 100c as the sign of the correction amount y _7, averaged without offsetting the output y ₁ ~y ₃ of the first to third filter 100a~100c correction in the position to be corrected luminance by the amount y _7, the correction amount y ₇ is suitably either positive or negative sign is set appropriately without being 0, it is possible to perform the correction.

Incidentally, as described above, the output y ₃ of the third filter 100c having the lowest frequency characteristic is also zero for an input image with very little change in luminance (very low frequency). However, it is considered that an input image with very little change in luminance does not include an edge. For this reason, edge enhancement processing is not necessary for such an input image in the first place. Therefore, no problem occurs even if the correction amount y ₇ becomes 0 because the sign of the output y ₃ is not determined.

7, in this embodiment, is a schematic diagram showing an output y ₁ ~y ₃ of the first to third filter 100a~100c against sharp edges typified by noise. More specifically, FIG. 7A is a schematic diagram showing the pre-process luminance signal Y, FIG. 7B is a schematic diagram showing the output y ₁ of the first filter, and FIG. FIG. 7D is a schematic diagram showing the output y _{2 of the} second filter, and FIG. 7D is a schematic diagram showing the output y ₃ of the third filter. The frequency component of the pre-process luminance signal Y in FIG. 7A is included in the range indicated by symbol EXB in FIG. 4 with the upper limit being the frequency at which the gains of the first filter 100a and the second filter 100b are equal. To do. Specifically, in the pre-process luminance signal Y shown in FIG. 7A, a luminance change corresponding to the frequency at which the gains of the first filter 100a and the second filter 100b are equal occurs in the vicinity of the position ED. In the vicinity of the pixel position (hereinafter referred to as “position EDB”) indicated by the symbol EDB on the slightly brighter side and in the vicinity of the pixel position indicated by symbol EDC (hereinafter referred to as “position EDC”) on the slightly darker side than the position ED. 2 The luminance change corresponding to the frequency at the peak of the pass band of the filter 100b occurs, and is slightly near the pixel position (hereinafter referred to as “position EDA”) indicated by the symbol EDA slightly brighter than the position EDB and slightly below the position EDC. At the peak of the pass band of the third filter 100c in the vicinity of the pixel position (hereinafter referred to as “position EDD”) indicated by the dark side code EDD. It shall luminance variation corresponding to the frequency is generated.

In FIG. 7A, for convenience of explanation, only a portion of noise that changes from dark to bright with reference to the left side of the drawing is shown. However, in practice, a portion of noise that changes from bright to dark with reference to the left side of the figure is present on the right side of the curve shown in FIG. As the type of the noise, there is also what the luminance change is steeper than the example shown in FIG. 7 (a), where the different sign of the output y ₁ ~y ₃ of the first to third filter 100a~100c For the sake of illustration, for the sake of convenience, description will be made by taking as an example the noise of luminance change of the degree shown in FIG.

The first filter 100a, as shown in FIG. 7 (b), a positive value in the bright side across the position ED, obtain an output y ₁ to a negative value in the dark side across the position ED. That is, the first filter 100a obtains an output y ₁ that emphasizes the luminance change near the position ED.

In contrast, the second filter 100b becomes a positive value in the bright side across the position EDB, with a negative value in the dark side across the position EDB, the output y ₂ bright side across the position EDC The output y ₂ becomes a positive value and becomes a negative value on the dark side across the position EDC. That is, the second filter 100b obtains an output y ₂ that emphasizes the luminance change in the vicinity of the position EDB and in the vicinity of the position EDC. As can be seen from FIG. 7C, the output y ₂ has a negative value on the bright side across the position ED and a positive value on the dark side across the position ED. Acts in the direction of suppressing changes.

The third filter 100c is a positive value in the bright side across the position EDA, with a negative value in the dark side across the position EDA, positive output y ₂ bright side across the position EDD An output y ₃ that becomes a negative value on the dark side across the position EDD is obtained. That is, the third filter 100c obtains an output y ₃ that emphasizes the luminance change in the vicinity of the position EDA and in the vicinity of the position EDD. As can be seen from FIG. 7D, the output y ₃ has a negative value on the bright side across the position ED and a positive value on the dark side across the position ED. Acts in the direction of suppressing changes.

As described above, in the example shown in FIGS. 7A to 7D, when attention is paid to the position ED where the luminance change of the luminance signal Y before processing is the largest, the output y ₁ of the first filter is in the vicinity of the position ED. The output y ₂ of the second filter and the output y ₃ of the third filter act in a direction to suppress the luminance change in the vicinity of the position ED, while acting in the direction of enhancing the luminance change. As described above, with respect to an input image including noise, the output signs of the filters differ depending on the pixel position, and the output y ₂ of the second filter and the output y ₃ of the third filter suppress noise. Act on. It should be noted that the example of the case where the output codes of the respective filters are different here is merely an example, and the sign of the output of each filter may be different in various cases in an actual input image having a more complicated luminance change. I want to be.

<1.3 Before and after edge enhancement processing>
As shown in the above equations (1), (2), and (3), the post-processing luminance signal Y1 and the post-correction first and second color difference signals C _b 1 and C _r 1 are the pre-processing luminance. signal Y and the pre-correction first, has a respective value obtained by multiplying the first coefficient α to the second color difference signal C _b, C _r. Accordingly, the ratio between the pre-processing luminance signal Y and the first and second color difference signals C _b and C _r before correction, the post-processing luminance signal Y1 and the first and second color difference signals C _b and C before correction. The ratio with _r1 is equal to each other. That is, the ratio between luminance and color difference is maintained before and after edge enhancement processing.

FIG. 8 is a diagram showing C _{b Cr} coordinates. In the C _r C _b coordinate, the saturation r is given by the following equation (10).

Equation (10), equation (2), and (3) from the pre-correction first color difference signal C _b and the first color difference signal after correction before correction and the saturation r obtained by the second color difference signal C _r C _b 1 The relationship with the saturation r1 obtained from the corrected second color difference signal C _r 1 can be _expressed by the following equation (11).
r1 = α · r (11)
From equation (11), it can be seen that the saturation changes at the same ratio as the luminance change rate by the edge enhancement processing. That is, as described above, maintaining the ratio between luminance and color difference before and after edge enhancement processing means that the ratio between luminance (corresponding to lightness) and saturation is maintained before and after edge enhancement processing. To do.

式（１２）、式（２）、および式（３）から、エッジ強調処理前後で色相θは変化しないことがわかる。 The hue θ is given by the following equation (12).

From the equations (12), (2), and (3), it can be seen that the hue θ does not change before and after the edge enhancement processing.

<1.4 Effect>
According to this embodiment, in an image processing apparatus that performs edge enhancement processing on an image indicated by an image signal obtained by receiving a television broadcast or obtained from a video system, the first coefficient α is used before correction. Since the first and second color difference signals C _b and C _r are corrected, the color difference change is determined according to the luminance change due to edge enhancement. More specifically, the first pre-correction, the second color difference signal C _b, by the first coefficient α is multiplied by C _r, color difference changes in proportion to the brightness. When the luminance increases due to edge enhancement, the color difference increases in proportion to the luminance, so that the ratio between the luminance and the color difference is maintained before and after the luminance correction. For this reason, it is possible to suppress fading that may occur due to a relatively small color difference with respect to luminance. Further, even when the luminance is reduced by edge enhancement, the color difference is reduced in proportion to the luminance, so that the ratio between the luminance and the color difference is maintained before and after the luminance correction. As a result, it is possible to prevent colors from becoming unnaturally bright due to a relatively large color difference with respect to luminance.

Further, according to this embodiment, when generating the correction amount y _7, the output y ₄ is the sum of the absolute value of the output y ₁ ~y ₃ different from the first to third filter 100a~100c frequency characteristics from each other the because of the use of the output y ₅ multiplied by the second coefficient k, the correction amount y ₇ averaged without offsetting the output y ₁ ~y ₃ of the first to third filter 100a~100c is obtained. Further, since the sign of the output y ₃ of the third filter 100c having the lowest frequency characteristic among the first to third filters 100a to 100c is used as the sign of the correction amount y ₇ , the luminance change is extremely small (the frequency change). The sign of the correction amount y ₇ is appropriately set according to the sign of the output y ₃ of the third filter 100 c from which output results are obtained in all input images except for the extremely small input image. For example, for an input image relatively thick edge is included, as described above, a value obtained by averaging without offsetting the output y ₁ ~y ₃ of the first to third filter 100a-100c (the output y ₅ ) acts in a direction to properly emphasize the edge. On the other hand, for an input image including noise, the sign of the output y ₃ of the third filter 100c, which is a sign that acts in the direction of suppressing noise, is used as the sign of the correction amount y ₇ . It averaged value without offsetting the output y ₁ ~y ₃ of the third filter 100a-100c (the output y ₅₎ acts in a direction to suppress the noise. In this way, it is possible to emphasize a relatively thick edge while suppressing noise.

<2. Second Embodiment>
<2.1 Configuration>
FIG. 9 is a block diagram showing a functional configuration of a main part of an image processing apparatus according to the second embodiment of the present invention. As shown in FIG. 9, the image processing apparatus, an image processing apparatus according to the first embodiment is obtained by adding the RGB-YC _b C _r conversion unit 50 as the luminance and color difference conversion unit. The RGB-YC _{b Cr} conversion unit 50 is implemented by software by the CPU 1. Since other configurations and operations are the same as those in the first embodiment, description thereof is omitted. The image processing apparatus according to the present embodiment corrects an input image indicated by an input image signal received from a multimedia system. Therefore, unlike the first embodiment, in this embodiment, the input image signal IN includes a red signal R, a green signal G, and a blue signal B.

RGB-YC _b C _r conversion unit 50 receives the red signal R, green signal G, and a blue signal B, the first front thereof pretreatment luminance signal Y and the correction, a second color difference signal C _b, converted to C _r To do. RGB-YC _b C _r conversion unit 50 gives the converted pretreated luminance signal Y to the edge enhancement unit 10 and the coefficient acquisition section 20, the first pre-correction, the second color difference signal C _b, the C _r first, The two color difference correction multiplying units 31 and 32 are respectively provided. Here, the signal conversion in the RGB-YC _{b Cr} conversion unit 50 is performed based on the following equation (13).

Since the operation after the signal format conversion by the RGB-YC _{b Cr} converter 50 in this embodiment is the same as that in the first embodiment, the description thereof is omitted.

<2.2 Effect>
According to the present embodiment, when edge enhancement processing is performed on an image indicated by an image signal received from a multimedia system, the same effect as in the first embodiment can be obtained.

<3. Third Embodiment>
<3.1 Configuration>
FIG. 10 is a block diagram illustrating a functional configuration of a main part of an image processing apparatus according to the third embodiment of the present invention. As shown in FIG. 10, the image processing apparatus is obtained by adding a coefficient adjustment unit 33 to the color difference correction unit 30 of the image processing apparatus according to the first embodiment. Since other configurations and operations are the same as those in the first embodiment, description thereof is omitted.

ここで、α１は係数調整部３３による調整後の第１係数（以下「調整後第１係数」という。）を表す。係数調整部３３は、調整後第１係数α１を第１，第２色差補正用乗算部３１，３２に与える。 The coefficient adjustment unit 33 receives the first coefficient α from the coefficient acquisition unit 20 and adjusts the first coefficient α. More specifically, as shown in the following equation (14), the coefficient adjustment unit 33 keeps the first coefficient α when the first coefficient α is 1 or more, and when the first coefficient α is smaller than 1, Adjustment is performed so that the first coefficient α is 1.

Here, α1 represents the first coefficient after adjustment by the coefficient adjustment unit 33 (hereinafter referred to as “first coefficient after adjustment”). The coefficient adjusting unit 33 supplies the adjusted first coefficient α1 to the first and second color difference correcting multiplying units 31 and 32.

  Thus, in the present embodiment, the adjusted first coefficient α1 is used for color difference correction instead of the first coefficient α. For this reason, when the first coefficient α is 1 or more, that is, when the luminance increases or does not change due to edge enhancement, the same color difference correction result as in the first embodiment can be obtained, so that fading is suppressed. . On the other hand, when the first coefficient α is smaller than 1, that is, when the luminance is decreased by edge enhancement, color difference correction is not performed. As a result, when the luminance is reduced by edge enhancement, the color becomes brighter than the original color due to a relatively large color difference with respect to the luminance. However, when a vivid color image is required, it is desirable to actively utilize the fact that the color becomes brighter than the original. In such a case, the present embodiment using the adjusted first coefficient α1 as represented by the above formula (14) is preferable.

<3.2 Effects>
According to the present embodiment, the color difference does not change when the luminance is reduced by edge enhancement. For this reason, a vivid output image in which only fading is suppressed can be obtained.

  The adjustment method of the first coefficient α by the coefficient adjustment unit 33 is not limited to that based on the above formula (14), and various other adjustment methods can be used.

<4. Fourth Embodiment>
<4.1 Configuration>
FIG. 11 is a block diagram showing a functional configuration of a main part of an image processing apparatus according to the fourth embodiment of the present invention. As shown in FIG. 11, the image processing apparatus, instead of the color difference correction unit 30 of the image processing apparatus according to the first embodiment, the primary color correction unit 60 in the subsequent stage of the YC _b C _r-RGB conversion unit 40 It is provided. In the present embodiment, the primary color correction unit 60 realizes a color correction unit. Since other configurations and operations are the same as those in the first embodiment, description thereof will be omitted as appropriate.

YC _b C _r-RGB conversion unit 40 converts the luminance signal Y, first, second color difference signal C _b, the C _r red signal R, blue signal B, and the green signal G. YC _b C _r-RGB conversion unit 40 gives a red signal R, blue signal B, and the green signal G to the primary color correction unit 60.

  The primary color correction unit 60 includes first to third primary color correction multiplication units 61 to 63. The primary color correction unit 60 corrects the red signal R, the blue signal B, and the green signal G using the first coefficient α received from the coefficient acquisition unit 20.

The first primary color correction multiplication unit 61 corrects the red signal R. More specifically, the first primary color correction multiplication unit 61 corrects the red signal R to a red signal R1 given by the following equation (15).
R1 = α · R (15)
Hereinafter, the red signal R before correction by the first primary color correction multiplication unit 61 is referred to as “pre-correction red signal”, and the red signal R1 after correction is referred to as “corrected red signal”.

The second primary color correction multiplying unit 62 corrects the green signal G. More specifically, the second primary color correction multiplying unit 62 corrects the green signal G to a green signal G1 given by the following equation (16).
G1 = α · G (16)
Hereinafter, the green signal G before correction by the second primary color correction multiplying unit 62 is referred to as “green signal before correction”, and the green signal G1 after correction is referred to as “green signal after correction”.

The third primary color correction multiplication unit 63 corrects the blue signal B. More specifically, the third primary color correction multiplying unit 63 corrects the blue signal B to the blue signal B1 given by the following equation (17).
B1 = α · B (17)
Hereinafter, the blue signal B before correction by the third primary color correction multiplication unit 63 is referred to as “pre-correction blue signal”, and the corrected blue signal B1 is referred to as “corrected blue signal”.

  The primary color correction unit 60 gives the output unit 5 an output image signal composed of the corrected red signal R1, the corrected green signal G1, and the corrected blue signal B1 obtained as described above.

<4.2 Effects>
According to this embodiment, since the red signal R before correction, the green signal G before correction, and the blue signal B after correction are corrected using the first coefficient α, the primary color change is determined according to the luminance change due to edge enhancement. Is done. More specifically, by multiplying the red signal R before correction, the green signal G before correction, and the blue signal B after correction by the first coefficient α, the primary color changes in proportion to the luminance. From the viewpoint of the luminance signal and the color difference signal, the corrected red signal R1, the corrected green signal G1, and the corrected blue signal B1, which are the primary color signals corrected by the primary color correction unit 60, are changed according to the luminance change due to edge enhancement. By determining the primary color change, the ratio between the luminance and the color difference is maintained before and after the luminance correction. Thus, also in this embodiment, the same effects as those of the first embodiment can be obtained.

In this embodiment, the RGB-YC _{b Cr} conversion unit 50 may be provided as in the second embodiment, or the coefficient adjustment unit 33 may be provided as in the third embodiment. Anyway.

<5. Other>
In the first embodiment, the example in which three filters having different frequency characteristics are used has been described, but the present invention is not limited to this. There may be two filters having different frequency characteristics, or four or more filters. The frequency characteristics of the plurality of filters may be different from each other and are not limited to the example shown in FIG. In addition, a high-pass filter is not essential as a filter used in the present invention, and only two or more band-pass filters having different frequency characteristics may be used.

  Further, the configuration and operation of the edge enhancement unit 10 described in the first embodiment is merely an example, and the present invention is not limited to this. Note that the present invention can also be applied to other luminance correction modes regardless of edge enhancement. In addition, the above-described embodiments can be variously modified and implemented without departing from the spirit of the present invention.

  As described above, according to the present invention, there are provided an image processing apparatus, an image processing method, an image processing program, and a recording medium storing an image processing program that suppress fading that may occur when performing luminance correction such as edge enhancement processing. can do.

1 ... CPU
3 ... Memory 6 ... Image processing program 10 ... Edge enhancement unit (luminance correction unit)
20 ... Coefficient acquisition unit 30 ... Color difference correction unit (color correction unit)
31, 32 color difference correction multiplication unit 33 ... coefficient adjusting unit 40 ... YC _b C _r -RGB converting unit (first signal format conversion portion)
50... RGB-YC _{b Cr} converter (second signal format converter)
60: Primary color correction unit (color correction unit)
61 to 63 ... primary color correction multiplying units 100a to 100c ... first to third filters 101 ... absolute value processing units 101a to 101c ... first to third absolute value processing units 103 and 105 ... luminance correction multiplying unit 104 ... sign acquiring unit 102, 106 ... adding unit IN ... input image signal OUT ... output image signal Y, Y1 ... luminance signal C _b, C _r ... color difference signals alpha, [alpha] 1 ... first coefficient k ... second coefficient

Claims (12)

An image processing apparatus for correcting an input image,
A luminance correction unit that performs correction for enhancing the edge of the input image with respect to the luminance signal indicating the input image ;
A coefficient acquisition unit that acquires a first coefficient that is a ratio of the luminance signal after correction to the luminance signal before correction;
A color correction unit that corrects a signal indicating the color of the input image based on the first coefficient ;
The brightness correction unit
A plurality of filters receiving the luminance signal and having different frequency characteristics from each other;
It is obtained by adding the output code of the filter having the lowest passband frequency among the plurality of filters to the value obtained by multiplying the absolute value obtained based on the outputs of the plurality of filters by the second coefficient. An image processing apparatus comprising: a correction processing unit that adds a correction amount to the luminance signal .   The image processing apparatus according to claim 1, wherein the color correction unit corrects a color difference signal indicating the input image based on the first coefficient.   The image processing apparatus according to claim 2, wherein the color correction unit multiplies the color difference signal by the first coefficient.   The color correction unit includes a coefficient adjustment unit that adjusts the first coefficient acquired by the coefficient acquisition unit, and multiplies the color difference signal by the adjusted first coefficient. Image processing device.   The image processing apparatus according to claim 4, wherein the coefficient adjustment unit sets the first coefficient to 1 when the first coefficient acquired by the coefficient acquisition unit is smaller than 1. 6. A primary color conversion unit that converts a luminance signal and a color difference signal before correction indicating the input image into a primary color signal;
The image processing apparatus according to claim 1, wherein the color correction unit corrects the primary color signal obtained by the primary color conversion unit based on the first coefficient. The image processing apparatus according to claim 1 , wherein the absolute value is a sum of absolute values of outputs of the filters.   The image processing apparatus according to claim 1, wherein the input image is indicated by a luminance signal and a color difference signal.   The image processing apparatus according to claim 8, further comprising a luminance / color difference conversion unit that converts a primary color signal indicating the input image into a luminance signal and a color difference signal indicating the input image. An image processing method for correcting an input image,
A luminance correction step for performing correction for emphasizing an edge of the input image with respect to the luminance signal indicating the input image ;
A coefficient acquisition step of acquiring a first coefficient that is a ratio of the luminance signal after correction to the luminance signal before correction;
Based on the first coefficient, Bei example a color correction step of correcting a signal indicating the color of the input image,
The brightness correction step includes
Providing the luminance signal to a plurality of filters having different frequency characteristics;
It is obtained by adding the output code of the filter having the lowest passband frequency among the plurality of filters to the value obtained by multiplying the absolute value obtained based on the outputs of the plurality of filters by the second coefficient. And a correction processing step of adding a correction amount to the luminance signal . An image processing program for correcting an input image,
A luminance correction step for performing correction for emphasizing an edge of the input image with respect to the luminance signal indicating the input image ;
A coefficient acquisition step of acquiring a first coefficient that is a ratio of the luminance signal after correction to the luminance signal before correction;
Causing the computer to execute a color correction step of correcting a signal indicating the color of the input image based on the first coefficient ;
The brightness correction step includes
Providing the luminance signal to a plurality of filters having different frequency characteristics;
It is obtained by adding the output code of the filter having the lowest passband frequency among the plurality of filters to the value obtained by multiplying the absolute value obtained based on the outputs of the plurality of filters by the second coefficient. An image processing program comprising: a correction processing step of adding a correction amount to the luminance signal .   A computer-readable recording medium on which the image processing program according to claim 11 is recorded.

Images