JP3424060B2 - Gradation correction device and video signal processing device using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gradation correction device and a video signal processing device using the same.

This gradation correction device and video signal processing device are used, for example, in a video camera.

[0003]

2. Description of the Related Art As a conventional gradation correction method, a histogram of brightness values of an input video signal for one screen is calculated and gradation conversion data is created according to the degree of dispersion of the calculated brightness values. It is known that gradation correction is performed based on this gradation conversion data.

[0004]

By the way, in the above-mentioned conventional example, the gradation of the input video signal is directly corrected. However, the input video signal may include not only a signal component but also an unnecessary noise component. In such a case, the contrast of the noise component will be emphasized by gradation correction. That is, in the conventional example, although the contrast of the image can be improved, there is room for improvement such as noise being noticeable.

Therefore, an object of the present invention is to obtain a high-quality image with improved contrast without making noise components in the screen noticeable in the gradation correction device.

Further, according to the present invention, in a video signal processing device to which a video signal in which a color signal is superimposed on a luminance signal is input, the contrast is improved without making noise components in the screen conspicuous, and the false color component The purpose is to obtain a high-quality image with suppressed occurrence.

[0007]

The present invention requires a screen
Input video signal for one screen by dividing into several areas
The divided, with respect to the signal component of each region, and so as to apply each gradation correction in accordance with the non-linear gradation correction characteristic, thereby the respective portions of the screen can be appropriately emphasized, respectively.

[0008]

[0009]

[0010]

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A gradation correction device according to claim 1 of the present invention comprises a signal dividing means for dividing an input video signal for one screen by dividing the screen into a required number of areas, and the input.
Histogram detection means for detecting a histogram representing the frequency of appearance of the video signal for each signal level, and the signal division means
For the input video signal of each area divided by
Based on the detected histogram by chromatogram detection means, a gradation correction characteristic setting means for creating respectively a nonlinear gradation correction characteristic, wherein for the signal component of the input image signal in each region, the gradation correction characteristic setting comprising a gradation correction means for performing gradation correction, respectively in accordance with the non-linear gradation correction characteristics set by the unit, and a video synthesis means for synthesizing the signal components of the tone correction each region.

[0012]

[0013] gradation correction apparatus according to claim 2 of the present invention, the gradation correction characteristic setting unit in claims 1, wherein the tone correction Patent
The tone setting means compares the histogram detected by the histogram detecting means with a required reference value, and changes those outside the required range to a specific value within the required range, thereby controlling the gradation of the gradient of the brightness level. A correction characteristic is to be created.

[0014] gradation correction apparatus according to claim 3 of the present invention, the gradation correction characteristic setting unit of the claim 2, wherein the gradation complement
The positive characteristic setting means, after creating the gradation correction characteristic in which the inclination of the brightness level is regulated, corrects the maximum level of the gradation correction characteristic which is lowered by the regulation processing in consideration of the reduction.

A video signal processing device according to claim 4 of the present invention is
A luminance color separating means for separating the video signal modulated color signal is superimposed on the luminance signal into a luminance signal and a color signal, according to claim 1 to 3 performs tone correction on the signal component of the separated luminance signal
And the described gradation correction device.

According to the video signal processing of claim 5 of the present invention, a luminance color separation means for separating a video signal in which a modulation color signal is superimposed on a luminance signal into a luminance signal and a color signal, and a signal component of the separated luminance signal. 4. The gradation correction device according to claim 1 , wherein the gradation correction is performed on the color correction signal, and the ratio of the separated color signal to the gradation-corrected luminance signal is the relationship before the gradation correction. Color signal correction means for performing the correction as described above , and synthesizing means for synthesizing the gradation-corrected luminance signal and the corrected color signal.

The details of the present invention will be described below with reference to the embodiments shown in FIGS.

(Embodiment 1) FIGS. 1 to 4 relate to Embodiment 1 of the present invention. FIG. 1 is a block diagram of a gradation correction device,
FIG. 2 is a block diagram of the histogram detecting means of FIG.
4 is a graph showing the histogram data and the gradation correction characteristic data, and FIG. 4 is a graph showing the frequency characteristic of the high pass filter of FIG. The first embodiment corresponds to claims 1 and 2.

In FIG. 1, A shows the whole gradation correction device, 1 is a histogram detection means, 2 is a gradation correction characteristic setting means, 3 is a gradation correction means, 4 is a signal separation means,
5 is a synthesizing means.

The histogram detection means 1 calculates the appearance frequency for each brightness level in the input video signal Sin for one screen. For example, as shown in FIG. 2, the level detection circuit 6, the multiplexer 7, and the selector 8 are provided. And the number of registers 9 corresponding to the number of brightness level divisions and the adder 10. In the first embodiment, the number of divisions of the brightness level is set to, for example, “16” in order to make the description easy to understand.
The level detection circuit 6 extracts the upper 4 bits of the input video signal Sin formed of a digital signal as a control signal for the multiplexer 7 and the selector 8. The multiplexer 7 and the selector 8 select, for example, one of 16 registers 9 according to the input signal level by the extracted 4-bit control signal. The adder 10 adds “1” to the output signal of the selected one register 9 and stores it in the same register 9 again. By performing this operation for one field period of the input video signal Sin, for example, histogram data H1 (1) to H1 (16) as shown by the band graph in FIG. 3A can be obtained.
Histogram data H1 obtained in this way
(1) to H1 (16) are transferred to the gradation correction characteristic setting means 2 within the blanking period of the input video signal Sin.

The gradation correction characteristic setting means 2 is composed of, for example, a microcomputer, and the histogram data H1 (1) to H1 supplied from the histogram detecting means 1 is used.
By obtaining the cumulative integration values SH1 (1) to SH1 (16) of (16), the first gradation correction characteristic data as shown by the line graph of FIG. 3A is created. The above-mentioned cumulative integration value SH1 (n) is obtained by the following equation.

[0022]

[Equation 1]

The gradation correction means 3 is based on the first gradation correction characteristic data provided from the gradation correction characteristic setting means 2.
The gradation correction processing is performed on the signal component output from the signal separating means 4 described below. This gradation correction processing is known processing such as γ correction using a gradation conversion table.

The signal separating means 4 includes, for example, a high pass filter 11, a clipping circuit 12, and a subtractor 13.
That is, the noise component Er is obtained by passing the input video signal Sin through the high pass filter 11 and then through the clipping circuit 12. Further, the subtracter 13 outputs the original signal component by subtracting the above-mentioned noise component Er from the input video signal Sin. The transfer characteristic of the high-pass filter 11 is as shown in FIG. 4, and is expressed by the following equation. In FIG. 4, the horizontal axis represents the frequency, the vertical axis represents the pass characteristic of the filter, and N represents the Nyquist frequency.

[0025]

[Equation 2]

The synthesizing means 5 is composed of an adder, adds the output signal of the gradation correcting means 3 and the noise component Er extracted by the signal separating means 4, and outputs a synthesized video signal Smix.

In the first embodiment described above, the input video signal is separated into the signal component and the noise component, and the non-linear gradation correction is applied only to the signal component.
It becomes possible to obtain a high-quality image with improved contrast so that noise is not noticeable.

Further, in the first embodiment, since the gradation-corrected luminance signal and the noise component separated before gradation correction are combined and output, the following effects can be obtained. That is, since the signal separation unit 4 is configured to separate the signal component of the specific frequency, when there is a signal component close to the specific frequency of the noise component, this signal component is separated together with the noise component. Sometimes. In such a case, strictly speaking, unless the above-described synthesizing process is performed, it cannot be said that a part of the image is lost. Therefore, in the first embodiment, it can be said that a faithful image without any omission can be obtained. Of course, even if the noise component is not combined, the image quality is not particularly deteriorated, so the above-described combining process may be omitted, and the omitted form is also included in the present invention.

(Second Embodiment) By the way, in the first embodiment, when the flat image portion in the screen contains a noise component which is not separated by the signal separating means 4, this noise component is emphasized. In addition, the contrast may not be improved so much in a subject having a small area. Furthermore, in the gradation correction processing of the first embodiment,
When the number of gradations of the original image is small, the contrast of the contour component may be overemphasized to generate a false contour component. In the second embodiment, such a thing can be avoided.

The second embodiment corresponds to claims 6 and 7, and the point different from the first embodiment is the processing content of the gradation correction characteristic setting means 2.

That is, in the gradation correction characteristic setting means 2,
Histogram data H1 (1) as shown in FIG.
To H1 (16), the histogram data H
1 (1) to H1 (16) are required reference values Hmax, Hm
By comparing with in, the upper limit reference value Hmax is set when it is larger than the upper limit reference value Hmax, and the lower limit reference value Hmin is set when it is smaller than the lower limit reference value Hmin, as shown in the band graph of FIG. 3B. The histogram data H2 (1) to H2 (16) are created, and the histogram data H2 (1) to H2 (16) are generated.
The second gradation correction characteristic data as shown by the solid line graph in FIG. 3B is created by obtaining the cumulative integration values SH2 (1) to SH2 (16).

In this way, in short, by setting the upper and lower limits of the histogram data H1 (1) to H1 (16) appropriately, the second floor in which the slope of the first gradation correction characteristic data is regulated is controlled. The key correction characteristic data is obtained. By using this second gradation correction characteristic data, it becomes possible to avoid excessive gradation correction. Therefore, even when a noise component that has not been separated by the signal separation unit 4 is included in the flat image portion, the noise component does not have to be emphasized, and the contrast can be improved even for a subject having a small area. To be Moreover, even if the number of gradations of the original video signal is small, the contrast of the contour component is not excessively emphasized, so that the occurrence of the false contour portion can be suppressed.

However, when the clipping process is performed as described above, the maximum value of the created second gradation correction characteristic data is as shown in FIG. 3 (a) as shown by the solid line in FIG. 3 (b). The value becomes lower than the maximum value of the first gradation correction characteristic data, and the dynamic range of the camera system cannot be fully utilized.

Therefore, in the second embodiment, in order to fully utilize the dynamic range of the camera system, after obtaining the second gradation correction characteristic data, the maximum of the second gradation correction characteristic data is obtained. The value is adjusted to be equal to the maximum value of the first gradation correction characteristic data. Specifically, in the gradation correction characteristic setting means 2, SH1 is set to each value of the histogram data SH2 (1) to SH2 (16).
The cumulative integrated values SH3 (1) to SH3 (16) are calculated by multiplying (16) / SH2 (16), and the cumulative integrated values SH3 (1) to SH3 (16) are used to calculate the values shown in FIG.
(B) The third gradation correction characteristic data indicated by the one-dot chain line is obtained. The gradation correction means 3 performs gradation correction according to the third gradation correction characteristic data created in this way.

Since the process other than the process described above is the same as that of the first embodiment, the duplicated description will be omitted.

(Embodiment 3) By the way, in the above-mentioned Embodiments 1 and 2, gradation correction is performed on the entire screen, but in this Embodiment 3, the screen is finely divided into a plurality of regions, and The gradation correction characteristic data is created for each area and the gradation is corrected separately.

5 to 7 relate to the third embodiment of the present invention. FIG. 5 is a block diagram of a gradation correction device, FIG. 6 is a schematic diagram showing a mode of screen division, and FIG. 6 is a graph showing histogram data and gradation correction characteristic data. The third embodiment corresponds to claim 4.

In order to make the explanation easy to understand, the third embodiment exemplifies a case where one screen is divided into four areas a, b, c and d, as shown in FIG. . Area a in FIG. 6 includes a high-intensity portion outside the window, and area c includes a relatively dark subject.

The gradation correction device A according to the third embodiment is the first
-Fourth histogram detecting means 1a to 1d, multiplexer 14 for selectively inputting the video signal of each area to each histogram detecting means 1a to 1d, and optimum gradation correction characteristic data for each area First to fourth gradation correction characteristic setting means 2a to 2d, a signal separating means 4 for separating a signal component and a noise component of the input video signal Sin,
The first to fourth gradation correcting means 3a to 3d, to which the input video signals from which the noise components have been separated are respectively input and which individually perform gradation correction, and the gradation correction are respectively performed by the gradation correcting means 3a to 3d. Areas a to d are extracted from the video signal for one screen, and they are combined to form a combined video signal Shmix.
And a control circuit 16 for controlling the multiplexer 14 and the video synthesizing circuit 15.
And a synthesizing means 5 for synthesizing the output signal Shmix of the video synthesizing circuit 15 with the noise component Er extracted by the signal separating means 4 and outputting the synthesized video signal Smix.

The operation will be described. For the input video signal Sin for one screen, the multiplexer 14 controlled by the control circuit 16 causes the signal in the area a in FIG. 6 to be the first histogram detecting means 1a and the signal in the area b in FIG. 6 to be the second histogram detecting means. 1b, the signal in the area c in FIG. 6 is input to the third histogram detecting means 1c, and the signal in the area d in FIG. 6 is input to the fourth histogram detecting means 1d.
Histogram data of the respective areas a to d as shown by the band graph of (d) are obtained. In addition, in the third embodiment, the number of divisions of the brightness level is set to “4” in order to make the description easy to understand.

The first to fourth gradation correction characteristic setting means 2a to 2d are the first to fourth histogram detecting means 1 respectively.
The histogram data of a to 1d are input, and the histogram data of FIG.
The gradation correction characteristic data of each area as shown by the polygonal line (d) is calculated and given to the first to fourth gradation correction means 3a to 3d.

On the other hand, the above-mentioned input image signal Sin for one screen is input to the signal separating means 4, and the signal separating means 4 separates the noise component to obtain the first to fourth gradation correcting means. 3a to 3d.

The first to fourth gradation correction means 3a to 3d are
With respect to the signal component of the input video signal Sin for one screen given from the signal separating means 4, the steps are individually performed based on the respective gray scale correction characteristic data given from the first to fourth gray scale correction characteristic setting means 2a to 2d. The tone is corrected and applied to the video synthesizing circuit 15. At this time, the first gradation correction unit 3a can perform the optimum gradation correction on the area a of the video signal for one screen, but the improper gradation correction on the areas b to d. The second gradation correcting means 3b can perform the optimum gradation correction on the area b of the video signal for one screen, but the area a, c, d is improperly gradation corrected. The three-tone correction means 3c can perform the optimum tone correction on the area c of the video signal for one screen, but the area a, b, and d can be inappropriately corrected. The gradation correction means 3d can perform the optimum gradation correction on the area d of the video signal for one screen, but the area a, b, and c are inappropriately corrected.

The image synthesizing circuit 15 appropriately synthesizes the signals Sha to Shd given by the first to fourth gradation correcting means 3a to 3d in accordance with the control signals x and y given from the control circuit 16. Obtain the signal Shmix. As the synthesizing process, only the signal of the region a, which is subjected to the optimum gradation correction, of the video signal Sha for one screen given from the first gradation correcting means 3a by the control signals x and y is used as the second gradation. Video signal Shb for one screen given from the correction means 3b
Among them, only the signal of the region b subjected to the optimum gradation correction is output, and only the signal of the region c subjected to the optimum gradation correction of the video signal Shc for one screen given from the third gradation correction means 3c. , Of the video signals Shd for one screen provided from the fourth gradation correcting means 3d, only the signals of the area d subjected to the optimum gradation correction are respectively selected, and the selected areas a to d are selected.
The signal of is synthesized. The control signals x and y are
As shown in FIG. 6 corresponding to the schematic view of the screen, x changes from “0” to “1” corresponding to the horizontal direction of the screen, and y
Corresponds to the vertical direction and changes from "0" to "1".

The relationship among the output signals Sha to Shd, the control signals x and y, and the combined signal Shmix is expressed by the following equation.

[0046]

[Equation 3]

Due to this relationship, the boundary portions of the respective areas a to d are combined in a natural state without a feeling of strangeness. Here, since the gradation correction characteristics corresponding to the respective areas a to d are different from each other, switching by a multiplexer or the like may cause a rapid change in Shmix at the boundary portion. Therefore, in the present embodiment, the composition ratio of the signals in each region is gradually changed according to the control signals x and y. For example, focusing on the horizontal direction, x becomes 0.5 at the center of the boundary between the regions a and b, and Shmi
x is an average value of Sha and Shb, the composition ratio of Shb is larger on the right side of the central part, and the composition ratio of Sha is larger on the left side of the central part. The same is true for the vertical direction.

In the third embodiment described above, the screen is finely divided into a plurality of areas a to d, and the areas a to d are individually subjected to gradation correction based on optimum gradation correction characteristic data. Since each part of the screen can be appropriately emphasized, a higher quality image can be obtained as compared with the first and second embodiments.

(Fourth Embodiment) In the third embodiment, the screen is divided into four areas a to d so that optimum gradation correction can be performed for each of the areas a to d. Depending on the situation, for example, the high-intensity part may be in a state of straddling each of the four areas a to d. In such a case,
In the third embodiment, the gradation correction is not always optimal. In view of this, in the fourth embodiment, the screen is divided into a high-luminance region and a low-luminance region, and gradation correction is performed separately for the high-luminance region and the low-luminance region.

8 to 10 relate to the fourth embodiment of the present invention. FIG. 8 is a block diagram of a gradation correction device, FIG. 9 is a schematic diagram showing a mode of screen division, and FIG. It is a graph which shows the histogram data and gradation correction characteristic data of b. The fourth embodiment corresponds to claim 5.

In the fourth embodiment, the screen is divided into a high-brightness area and a low-brightness area, and the gradation of each area is corrected separately.

The gradation correction apparatus A of the fourth embodiment has a high-brightness area detecting means 17 for detecting a high-brightness area, first and second histogram detecting means 1a and 1b, and respective histogram detecting means 1a and 1b. A multiplexer 14 for selectively inputting video signals in a low-luminance region and a high-luminance region,
First and second gradation correction characteristic setting means 2a for creating optimum gradation correction characteristic data for each of the low brightness area and the high brightness area.
2b, a signal separating unit 4 for separating a signal component and a noise component of the input video signal, and the input video signal from which the noise component has been separated are respectively inputted and each of the first and second gradation correction is performed. The low-brightness area a and the high-brightness area b are extracted and combined from the gradation correction means 3a and 3b and the video signals Sha and Shb for each one screen whose gradation is corrected by the gradation correction means 3a and 3b. Synthetic video signal Shm
A video composition circuit 15 for outputting ix, and a control circuit 1 for controlling the multiplexer 14 and the video composition circuit 15.
6, and the synthesizing means 5 for synthesizing the output signal Shmix of the video synthesizing circuit 15 with the noise component Er extracted by the signal separating means 4 and outputting the synthesized video signal Smix.

The operation will be described. The input video signal Sin is
It is input to the high brightness area detection means 17. The high-brightness region detecting means 17 divides the input video signal into regions of "48" in which the horizontal is "8" and the vertical is "6", as shown in FIG. Sm (1) ~
Calculate Sm (48). Higher brightness area detection means 1
7, the integral values Sm (1) to Sm (48) in the 48 areas are compared with a required reference value Sth, and the integral value is compared with the reference value St.
A region larger than h is recognized as a high brightness region, and a high brightness region detection signal representing the high brightness region is output to the control circuit 16. In FIG. 9, a region b surrounded by a thick line is a high luminance region, and the other region a is a low luminance region.

In the control circuit 16, the high brightness area detection circuit 1
The multiplexer 18 is controlled based on the high-brightness region detection signal input from 7. As a result, the input video signal Sin of one screen is divided into the low-brightness area a and the high-brightness area b, and the histogram detection means 1a and 1b and the gradation correction characteristic setting means 2a and 2b are used for the operation shown in FIGS. ), The histogram data and the gradation correction characteristic data of the two areas a and b are calculated. Here, as in the case of the third embodiment, the number of divisions of the brightness level is set to “4” for easy understanding of the description.

Further, the control circuit 16 generates the control signals x and y based on the high brightness area detection signal input from the high brightness area detecting means 17. The control signals x and y are shown in FIG. 9 in correspondence with the schematic view of the screen. As shown in FIG. 9, x changes from “0” to “1” corresponding to the horizontal direction of the screen,
y changes from "0" to "1" corresponding to the vertical direction.

The first and second gradation correction means 3a and 3b are
With respect to the signal component of the input video signal Sin for one screen provided from the signal separating means 4, the steps are individually performed based on the respective gradation correction characteristic data provided from the first and second gradation correction characteristic setting means 2a and 2b. The tone is corrected and applied to the video synthesizing circuit 15. At this time, the first gradation correction unit 3a can perform optimum gradation correction on the low-luminance area a of the video signal for one screen, but improper gradation correction on the high-luminance area b. In other words, the second gradation correction means 3b can perform optimum gradation correction on the high-brightness area b of the video signal for one screen, but it can perform inappropriate gradation correction on the low-brightness area a. . These gradation correction means 3a, 3b
In the case as shown in FIGS. 10A and 10B, the low-luminance area a in FIG. 9 is emphasized in the low-luminance portion, and the area b in FIG. 9 is emphasized in the high-luminance portion. Has become.

The video synthesizing circuit 15 synthesizes the signals Sha and Shb provided by the first and second gradation correcting means 3a and 3b in accordance with the control signals x and y provided from the control circuit 16, thereby producing a synthesized signal. Obtain Shmix and output it. As the synthesizing process, only the signal in the low-luminance region a for which the optimum gradation correction has been performed among the video signals Sha for one screen provided from the first gradation correction unit 3a, and the second gradation correction unit 3b. Video signal Sh for one screen given from
Only the signals in the high-brightness region b on which the optimum gradation correction is performed are selected from b, and the signals in the selected regions a and d are combined.

The signals Sha and Shb, the control signal x,
The relationship between y and the combined signal Shmix is expressed by the following equation.

[0059]

[Equation 4]

Due to this relationship, the boundary portion between the areas a and b is synthesized in a natural state without a feeling of strangeness. Here, since the gradation correction characteristics corresponding to the respective areas a to d are different from each other, the signals of the respective areas are gradually switched as in the third embodiment. The number of regions is the same as in the third embodiment.
However, the operation is the same although the above relational expression is different.

In the fourth embodiment described above, the screen is divided into the high-brightness area b and the low-brightness area a, and the gradations based on the optimum gradation correction characteristic data for the video signals of the areas a and b, respectively. Since the corrections are performed separately, natural gradation correction can be performed regardless of where the high-brightness region b is located on the screen depending on the shooting conditions, and an image with good visibility can be obtained.

(Fifth Embodiment) FIG. 11 is a block diagram of a video signal processing apparatus according to the fifth embodiment of the present invention. The fifth embodiment corresponds to claims 8 and 9.

In the fifth embodiment, for example, gradation correction can also be performed on the output signal of the single-plate color solid-state image pickup element which performs colorization by a single element. The output signal of such a single-plate color solid-state imaging device has a form in which a color signal component is superimposed on a luminance signal component, and the tone correction device A of the above-described first to fourth embodiments responds to such a signal. If the gradation correction process is performed in step 2, the non-linear characteristic may cause the balance between the luminance signal component and the color signal component to be lost, and a false color component may be generated. Therefore, in the fifth embodiment, regarding the color video signal in which the color signal component is superimposed on the luminance signal component,
First, a luminance signal component and a color signal component are separated, only the luminance signal component is subjected to the tone correction processing according to any one of the above-described first to fourth embodiments, and then the generation of the false color component is suppressed. I am trying to apply.

The video signal processing apparatus according to the fifth embodiment has a luminance / color separation circuit 19, the gradation correction apparatus A according to the first embodiment, a low-pass filter 20, and a luminance / color synthesis circuit 21.
It has and.

The luminance color separation circuit 19 is provided with an input video signal Sin in which a color signal component is superimposed on the luminance signal, and the input video signal Sin is supplied to the luminance signal component Y0 and the color signal component C.
0, and a high-pass filter 22 for extracting a color signal component C0 from the input video signal Sin, and a color signal component C0 extracted by the high-pass filter 22 is subtracted from the input video signal Sin to obtain a luminance signal component Y0. The subtractor 23 for extracting and the color signal component C0 extracted by the high-pass filter 22 are divided by the luminance signal component Y0 extracted by the subtractor 23 to obtain a standardized color signal component C1. .

The gradation correction device A performs the same gradation correction as that of the first embodiment on the luminance signal Y0 separated by the luminance color separation circuit 19. However, since the gradation correction device A performs nonlinear gradation correction, high-frequency nonlinear distortion may occur to some extent. If the luminance signal having such non-linear distortion is later combined with the color signal to form a color video signal, the non-linear distortion component is reproduced as a false color signal when the color video signal is reproduced. Therefore, the non-linear distortion component is removed by the low pass filter 20.

The low-pass filter 20 is a gradation correction device A.
The high-frequency non-linear distortion component included in the gradation-corrected luminance signal is removed, and the filter characteristic is set to remove the high-frequency non-linear distortion component.

The luminance color synthesis circuit 21 has a luminance signal Y2 from which the non-linear distortion component is removed by the low-pass filter 20 and a color signal component C1 standardized by the divider 24 of the luminance color separation circuit 19.
And a luminance signal Y output from the low-pass filter 20. The multiplier 25 that obtains the weighted color signal component C2 by multiplying by and the color signal component C2 obtained by the multiplier 25
And an adder 26 that obtains a composite video signal Sout by adding to 2.

Here, the relationship between the luminance signal and the color signal of each of the above parts is expressed by C0 / Y0 = C2 / Y2 = C1, where C0,
Since the ratio of the color component and the luminance component is saved in both C2,
There is no change in the color signal, that is, a change in hue due to the non-linear gradation correction processing of the gradation correction device A.

In the fifth embodiment described above, regarding the video signal in which the color signal component is superimposed on the luminance signal component,
It is possible to suppress the occurrence of false color components while improving contrast without making noise noticeable.

The present invention is not limited to the above embodiments, and various applications and modifications are conceivable.

(1) In the above-described first and second embodiments, the synthesizing unit 5 synthesizes the signal component whose tone is corrected by the tone correcting unit 3 and the noise component which is extracted by the signal separating unit 4. It is not necessary to combine the noise component with the corrected signal component.

(2) In the second embodiment described above, the clipping processing of the histogram data by the gradation correction characteristic setting means 2 and the maximum value adjustment processing of the gradation correction characteristic are either program control processing by a microcomputer or circuit processing. You can also do it. (3) In the third embodiment, one screen is equally divided into four blocks a to d, but the number of divisions is arbitrary.
In addition, in the third embodiment, four gradation correction characteristic setting means 2 are provided.
Although a to 2d are used, time division processing may be performed using a single gradation correction characteristic setting means.

(4) In the fourth embodiment, one screen is divided into two areas, a low-brightness area a and a high-brightness area b, but it is more effective if it is divided into three or more areas stepwise. Gradation correction can be performed. Further, in the fourth embodiment, the screen is divided into 48 blocks, but the larger the number of divisions, the finer the range of control becomes,
At the maximum, it can be divided for each pixel. Furthermore, in the fourth embodiment, two types of gradation correction characteristic setting means 2 are provided.
Although a and 2b are used, time division processing may be performed using a single gradation correction characteristic setting means.

(5) In the fifth embodiment, an example in which the tone correction apparatus A of the first embodiment is used as the tone correction apparatus A included in the video signal processing apparatus B is described. The gradation correction device A can be used.

[0076]

[0077]

According to the first aspect of the present invention, the required number of areas are displayed on the screen.
By dividing the input video signal for one screen ,
Calculate the optimum gradation correction characteristics for each area,
Since gradation correction is performed based on each gradation correction characteristic, each part of the screen can be appropriately emphasized, and a higher quality image can be obtained.

[0078]

According to the second aspect , since the inclination of the gradation correction characteristic is regulated, it is possible to avoid excessively enhancing the contrast when performing the gradation correction.
Therefore, even if a flat image portion includes a noise component, the noise component does not have to be emphasized, and the contrast can be improved even for a subject having a small area. Moreover, even if the number of gradations of the original video signal is small, the contrast of the contour component is not excessively emphasized, so that the occurrence of the false contour portion can be suppressed.

[0080] According to claim 3, in the case of regulating the inclination of the tone correction characteristic as claimed in claim 2, it suffices to adjust the maximum level of gradation correction characteristic, the dynamic range of the camera system can be fully utilized As a result, a sufficient gradation correction effect can be obtained.

Further, in the video signal processing device of claims 4 and 5 , the video signal in which the color signal is superimposed on the brightness signal is divided into a brightness signal component and a color signal component, and only the brightness signal is defined. Since the gradation correction processing as shown in 3 is performed and the color signals are weighted according to the gradation correction of the luminance signal component, the contrast is improved without making noise components in the screen conspicuous. In addition, it is possible to obtain a high-quality image in which the generation of false color components is suppressed.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a gradation correction device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of the histogram detection means in FIG.

FIG. 3 is a graph showing histogram data and gradation correction characteristic data according to the first embodiment.

FIG. 4 is a graph showing frequency characteristics of the high pass filter according to the first embodiment.

FIG. 5 is a configuration diagram of a gradation correction device according to a third embodiment of the present invention.

FIG. 6 is a schematic diagram showing a form of screen division according to the third embodiment.

FIG. 7 is a graph showing histogram data and gradation correction characteristic data of each area according to the third embodiment.

FIG. 8 is a configuration diagram of a gradation correction device according to a fourth embodiment of the present invention.

FIG. 9 is a schematic diagram showing a form of screen division according to the fourth embodiment.

FIG. 10 is a graph showing histogram data and gradation correction characteristic data of each area according to the fourth embodiment.

FIG. 11 is a configuration diagram of a video signal processing device according to a fifth embodiment of the present invention.

[Explanation of symbols]

A gradation correction device 1 Histogram detection means 2 gradation correction characteristic setting means 3 gradation correction means 4 Signal separation means 5 Synthetic means

Continuation of the front page (56) Reference JP-A-5-268498 (JP, A) JP-A-7-162715 (JP, A) JP-A-63-84526 (JP, A) JP-A-3-126377 (JP , A) JP-A-5-268622 (JP, A) JP-A-6-14325 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04N 5/20

Claims (5)

(57) [Claims] 1. By dividing the screen into a required number of areas
Therefore, the signal dividing means for dividing the input video signal for one screen, the histogram detecting means for detecting the histogram showing the appearance frequency of the input video signal for each signal level, and the respective areas divided by the signal dividing means. For input video signal
For, on the basis of the detected human <br/> Sutoguramu by the histogram detecting unit, the gradation correction characteristic setting means for creating respectively a nonlinear gradation correction characteristic, wherein for the signal component of the input image signal in each region , the gradation correction characteristic and the gradation correcting means for performing gradation correction, respectively in accordance with the non-linear gradation correction characteristic set by the setting means, image combining means for combining the signal components of the tone correction the regions And a gradation correction device comprising: 2. The gradation correction characteristic setting means is the hysteresis.
Histogram detected by the togram detection means is the required standard
Compare with the value, and if the value is out of the required range,
By changing to a specific value within the range, the brightness level
To create a gradation correction characteristic that regulates the
Item 1. The gradation correction device according to item 1 . Wherein said gradation correction characteristic setting unit, the luminance level
After creating a gradation correction characteristic that regulates the
The maximum level of gradation correction characteristics
3. The correction is made in consideration of the decrease.
Built-in tone correction device. 4. An image in which a modulation color signal is superimposed on a luminance signal
Luminance color separation means for separating the signal into a luminance signal and a color signal, and gradation correction for the signal component of the separated luminance signal
A video signal processing device , comprising: the gradation correction device according to claim 1 . 5. A luminance color separation means for separating a video signal in which a modulated color signal is superimposed on a luminance signal into a luminance signal and a color signal, and gradation correction is performed on the signal component of the separated luminance signal. The gradation correction device according to any one of 1 to 3 and the separated
The ratio of the color signal to the gradation-corrected luminance signal is
Color signal correction means for performing correction so as to obtain the relationship before the tone correction
And the gradation-corrected luminance signal and the corrected color signal
And a synthesizing means for synthesizing the video signal and the video signal processing device.