JPH0690382A - Gradation correction device - Google Patents

Abstract

PURPOSE:To implement gradation correction processing with a large correction effect without causing deteriorated gradation near a black and a white level of a video signal. CONSTITUTION:The device is provided with a black level correction table 20 suppressing a correction when gradation is corrected in a direction of a black level, in addition to gradation correction by a brightness histogram using a luminance signal as a parameter. Similarly the device is provided with a white level correction table 21 to suppress the correction in a white level direction. A correction arithmetic operation circuit 22 uses the tables to generate a luminance signal not causing deteriorated gradation even near a black level and a white level. Thus, the gradation correction processing with a large correction effect is implemented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a television receiver,
The present invention relates to a gradation correction device that corrects the gradation of a video signal in a video device such as a video tape recorder, a video camera, a video disc.

[0002]

2. Description of the Related Art In recent years, as color television receivers have become larger in size and have higher image quality, there has been a demand for a gradation correction device in order to make an image look clearer. Many gradation correction devices correct the gradation of a video signal by passing the video signal through a non-linear amplifier to expand the dynamic range of the video on the CRT.

An example of a conventional gradation correction device will be described. FIG. 3 is a block diagram showing a configuration example of a conventional gradation correction device. In the figure, an A / D converter 1 is a circuit that converts an input luminance signal into a digital value. The histogram memory 2 is a memory that creates luminance histogram data from the luminance signal output from the A / D converter 1 and holds this data. The histogram memory 2 associates the brightness level of the input signal with the address of the memory and uses the frequency of the brightness distribution of the brightness signal as its data.

The histogram calculation circuit 3 calculates the average value, mode value, minimum value, maximum value, deviation coefficient, white area, black area, etc. of the luminance signal from the data in the histogram memory 2.
From these calculation data, limiter level, constant addition value,
This circuit calculates and outputs each control value such as cumulative start brightness level, cumulative stop brightness level, maximum brightness level. The output of the histogram calculation circuit 3 is output to the limiter / adder circuit 4, the cumulative control register circuit 5, and the normalization control register circuit 6, respectively.

The limiter / adder circuit 4 reprocesses the data in the histogram memory 2 and, depending on the limiter level given from the histogram calculation circuit 3, limits the frequency of the luminance histogram to a certain level or above. , A circuit that corrects the level of the luminance histogram by adding a constant addition value. The corrected histogram data processed by the limiter / adder circuit 4 is stored in the histogram memory 2 again.

The histogram cumulative control register circuit 5 is a circuit for giving the cumulative cumulative start luminance level and cumulative cumulative stop luminance level to the histogram cumulative addition circuit 7 when the cumulative histogram is obtained. The histogram cumulative addition circuit 7 is a circuit that accumulates the reprocessed data stored in the histogram memory 2 based on the cumulative start luminance level and the cumulative stop luminance level held in the cumulative control register circuit 5 to calculate a cumulative histogram. .

The cumulative histogram memory 8 is a memory for storing the result of cumulative calculation of the histogram cumulative addition circuit 7. This memory 8 also inputs the brightness level to the address,
The frequency is input to the data. The normalization control register circuit 6 outputs the necessary data to the look-up table operation circuit 9 when the look-up table is created by normalizing the data of the cumulative histogram stored in the cumulative histogram memory 8. . That is, when the normalization control register circuit 6 receives the maximum brightness level of the brightness signal after normalization from the histogram calculation circuit 3, it outputs a normalization coefficient corresponding to the value.

The look-up table arithmetic circuit 9 is a circuit for normalizing the data of the cumulative histogram memory 8 based on the output signal of the normalization control register circuit 6. The look-up table 10 is a memory that stores the data normalized by the look-up table calculation circuit 9. The look-up table 10 uses the brightness level as an address and stores the frequency as the data. The timing control circuit 11 is a circuit that gives a clock signal and a timing signal necessary for the operation of each circuit unit, and controls the arithmetic order of each circuit unit and each memory.

The correction calculation circuit 13 inputs the correction signal read from the look-up table 10 and the video signal output from the A / D converter 1 by using the brightness level of each pixel as an address, and the gradation is obtained. This is a circuit for performing correction calculation.
The D / A converter 14 is a circuit that converts the digital signal from the correction calculation circuit 13 into an analog luminance signal.

The operation of the gradation correction device configured as described above will be described. 4 and 5 are explanatory diagrams showing the operation characteristics of each circuit portion of the gradation correction circuit. First, the video luminance signal of the television is sampled for each frame. The number of sampling points is set to a large number in order to uniformly sample the screen, and the luminance signal a is input to the A / D converter 1. The A / D converter 1 converts an analog luminance signal into a digital luminance signal b.

The histogram memory 2 stores the luminance signal b
Is used as the address, and the limiter / adder circuit 4 adds and counts the number of data inputs at that address, and holds the count result. By performing such an operation for one vertical scanning period, a luminance histogram of the input luminance signal a can be created. FIG. 4A illustrates a brightness histogram. Here, the luminance level of the input luminance signal is distributed in the range of Ya to Yb, there is no black level component of Ya or lower and a white level component of Yb or higher, and the signal has a narrow dynamic range. There are more bright image parts with a further brightness level Ym, and then a darker brightness level Ym.
It is assumed that there are many image parts of n.

Next, the histogram calculation circuit 3 reads out the data of the histogram memory 2 in which the brightness histogram is stored, and the average value, mode value, minimum value, maximum value, deviation coefficient, white area, black of the input brightness signal a. Calculate the area etc. Then, the histogram calculation circuit 3 obtains control values such as a limiter level, a constant addition value, a start luminance level and a stop luminance level for cumulative calculation, and a maximum luminance level after normalization from these calculation results, and these control values e To the limiter / adder circuit 4, the cumulative control register circuit 5, and the normalization control register circuit 6, respectively.

Next, the limiter / adder circuit 4 reads out the data shown in FIG. 4A from the histogram memory 2, slices the high frequency part of the histogram at the limiter level output from the histogram calculation circuit 3, and Correct to the state shown in b). In this correction, in an image having the same luminance component, each pixel has no difference in brightness and darkness, and the feature of the image is difficult to grasp. Therefore, the luminance change of a specific portion is emphasized to easily grasp the feature of the image. Further, the limiter / adder circuit 4 adds a constant addition value to the histogram shown in FIG. 4B, and corrects again the histogram shown in FIG. 4C.
This correction widens the dynamic range of an image having a narrow dynamic range of luminance from the black level side to the white level side.

The thus corrected histogram data is stored again in the histogram memory 2. The correction data is written to the histogram memory 2 within the vertical blanking period of the video signal so that the correction data is not updated during the gradation correction period of the video signal.
The result is output to the histogram cumulative addition circuit 7 as the corrected histogram data c. The histogram cumulative addition circuit 7 performs cumulative addition of the input data to create cumulative histogram data. In the cumulative histogram, the larger the constant addition value added by the limiter / adder circuit 4 is, the more linear the cumulative histogram is, and the smaller the constant addition value is, the larger the influence of the original histogram is.

Next, the histogram cumulative addition circuit 7 operates as shown in FIG.
As shown in (c), the cumulative control register circuit 5
The cumulative histogram data f of the corrected histogram data c within the range of the cumulative start luminance level Yp and the cumulative stop luminance level Yq given by the above is calculated, and the result is stored in the cumulative histogram memory 8. This data is shown in FIG. 5 (d).

The look-up table arithmetic circuit 9 reads the data from the cumulative histogram memory 8 and the maximum value of the cumulative histogram data is given by the normalization control register circuit 6 to the maximum output brightness level Yq (=
Find a normalization coefficient such that h). Based on this coefficient, the look-up table operation circuit 9 performs an operation on the cumulative histogram data g and stores the result i in the look-up table 10. At this time, operations such as automatic contrast control (ACL) and automatic bright control (ABL) can be performed by controlling the maximum output brightness level h. This relationship is shown in Figure 5.
It shows in (e). That is, with respect to the input brightness level, the output brightness level is centered on the solid line, and the characteristics are corrected and changed within the range shown by the dotted line.

Next, the correction arithmetic circuit 13 inputs the input luminance signal b.
The address j is used as an address to read the data j from the look-up table 10, and the data j and the input luminance signal b are used to perform the gradation correction calculation shown in FIG. 5E to obtain the corrected output luminance signal k. FIG. 5F shows a histogram of the corrected luminance signal. In FIG. 5F, it can be seen that the corrected luminance histogram has a dynamic range expanded to the range from the black level Yc to the white level Yd. Further, it can be seen that the distribution centered on the white peak level Ym spreads to the left and right as compared with FIG. 4A, and the dynamic range of the image portion having such brightness is also expanded. or,
The distribution centered on the black peak level Yn also spreads to the left and right as compared with FIG.

The D / A converter 14 converts the corrected output luminance signal k into an analog signal 1 and outputs the analog signal 1 to a display section of a video device (not shown). The timing control circuit 11
Controls the operation of each circuit so that the signal processing operation is performed in the order described above. (Reference: Japanese Patent Application No. 1-2
No. 65393 "Gradation correction device")

[0019]

In such a conventional gradation correcting apparatus, when the luminance distribution is concentrated in the input video signal as shown in FIG. 4A, the luminance histogram data is used. Then, the gradation is corrected centering on the concentrated luminance level. Although such a correction is effective for intermediate luminance, when there is a concentration of luminance at a luminance level slightly higher than the black level, a signal at a black level lower than this luminance level tends to have a lower luminance level. Correction is performed. At this time, if the effect of correcting the intermediate brightness is large,
On one screen, there was a problem that the gradation at the black level was lost.

Further, when there is a concentration of luminance at a luminance level slightly lower than the white level, a signal of a white level higher than this luminance level is corrected in the direction in which the luminance level becomes higher. At this time, if the effect of correcting the intermediate luminance is large, there is also a problem that the gradation at the white level is lost on a certain screen.

The present invention has been made in view of such conventional problems, and the invention according to claim 1 does not cause gradation collapse in the vicinity of the black level and the gradation is such that the overall correction effect becomes large. The purpose is to realize a correction device.

It is another object of the present invention to realize a gradation correction device which does not cause gradation collapse near the white level and has a large overall correction effect.

[0023]

According to a first aspect of the invention of the present application, an A / D converter for sampling an input video signal and digitally converting a luminance signal included in the signal, and an A / D converter
The brightness level of the digital brightness signal output from the converter is used as an address, the signal output frequency of each brightness level is input as data, and a histogram memory that creates and stores a brightness histogram and the data in the histogram memory is read out.
A parameter showing the characteristics of the luminance histogram is calculated from this data, the histogram calculation circuit that outputs the control value, the limiter level that the histogram calculation circuit outputs, and the constant addition value are given to the histogram memory, and the histogram stored in the histogram memory A limiter / adder circuit that corrects the shape and stores the corrected histogram data in the histogram memory again, and a cumulative control register circuit that extracts and outputs the signals of the cumulative start luminance level and the cumulative stop luminance level from the output of the histogram calculation circuit. And the normalization control register circuit that extracts and outputs the maximum brightness level from the output of the histogram calculation circuit, the output signal of the histogram memory and the output signal of the cumulative control register circuit, and the correction hysteresis of the histogram memory. Histogram cumulative addition circuit that reads the gram data and performs cumulative addition to calculate the cumulative histogram, cumulative histogram memory that stores the calculation result of the histogram cumulative addition circuit, and reads the data of the cumulative histogram memory and outputs the normalization control register circuit Based on the look-up table operation circuit that normalizes the data of the cumulative histogram memory using the signal, the look-up table that stores the data output from the look-up table operation circuit, and the output signal of the A / D converter, A black level correction table for outputting the black level correction suppression amount for suppressing the gradation correction of the brightness signal near the level in the black direction, and the output signal of the A / D converter are used as addresses to obtain from the look-up table. Correction signal and the correction control obtained from the black level correction table. Based on the amount, it is characterized in that it comprises a correction arithmetic circuit for performing a correction operation on the luminance signal outputted from the A / D converter, a.

According to a third aspect of the present invention, an A / D converter for sampling an input video signal and digitally converting a luminance signal included in the signal, and a luminance of a digital luminance signal output from the A / D converter. A level is used as an address, the signal output frequency of each brightness level is input as data, a histogram memory that creates and stores a brightness histogram and the data in the histogram memory are read, and from this data the parameters that characterize the brightness histogram are calculated. , The histogram calculation circuit that outputs the control value, the limiter level that the histogram calculation circuit outputs, and the constant addition value are given to the histogram memory, the shape of the histogram stored in the histogram memory is corrected, and the corrected histogram data is again stored in the histogram memory. Limiter / adder circuit to store in A cumulative control register circuit that extracts and outputs the signals of the cumulative start brightness level and the cumulative stop brightness level from the output of the RAM calculation circuit, and a normalization control register circuit that extracts and outputs the maximum brightness level from the output of the histogram calculation circuit And the output signal of the histogram memory and the output signal of the cumulative control register circuit are input, the corrected histogram data of the histogram memory is read, cumulative addition is performed to calculate the cumulative histogram, and the calculation result of the histogram cumulative addition circuit And a look-up table operation circuit that reads out the data of the cumulative histogram memory and normalizes the data of the cumulative histogram memory by using the output signal of the normalization control register circuit. A lookup table for storing the data output from the table calculation circuit,
A white level correction table for outputting a white level correction suppression amount for suppressing gray level correction of a luminance signal near the white level in the white direction based on the output signal of the A / D converter;
A correction operation is performed on the luminance signal output from the A / D converter based on the correction signal obtained from the look-up table and the correction control amount obtained from the white level correction table, using the output signal of the converter as an address. And a correction arithmetic circuit.

[0025]

According to the invention of claim 1 of the present application having such a feature, the A / D converter samples the input video signal at a specific cycle and digitally converts the luminance signal included in the signal. The histogram memory uses the brightness level of the digital brightness signal output from the A / D converter as an address, inputs the signal output frequency of each brightness level as data, and creates and stores a brightness histogram. The histogram calculation circuit reads the data in the histogram memory, calculates the parameters showing the characteristics of the luminance histogram from this data,
Output the control value. The limiter / adder circuit supplies the limiter level or constant addition value output from the histogram calculation circuit to the histogram memory, corrects the shape of the histogram stored in the histogram memory, and stores the corrected histogram data again in the histogram memory. The cumulative control register circuit extracts and outputs the signals of the cumulative start luminance level and the cumulative stop luminance level from the output of the histogram calculation circuit. The normalization control register circuit extracts and outputs the maximum brightness level from the output of the histogram calculation circuit. The histogram cumulative addition circuit inputs the output signal of the histogram memory and the output signal of the cumulative control register circuit, reads the corrected histogram data of the histogram memory, and cumulatively adds to calculate a cumulative histogram. The cumulative histogram memory stores the calculation result of the histogram cumulative addition circuit. The look-up table arithmetic circuit reads the data of the cumulative histogram memory and normalizes the data of the cumulative histogram memory using the output signal of the normalization control register circuit. The look-up table stores data output from the look-up table arithmetic circuit. On the other hand, the black level correction table is based on the output signal of the A / D converter.
The black level correction suppression amount for suppressing the gradation correction in the black direction of the luminance signal near the black level is output. Next, the correction arithmetic circuit uses the output signal of the A / D converter as an address and uses the correction signal obtained from the look-up table and the correction control amount obtained from the black level correction table to calculate A / D.
Correction calculation is performed on the luminance signal output from the D converter. By processing the brightness in this way, gradation collapse is not caused in the vicinity of the black level, and gradation correction for the entire brightness level can be effectively performed.

According to the invention of claim 3 of the present application, the A / D
The converter samples the input video signal at a specific cycle and digitally converts the luminance signal included in the signal. The histogram memory uses the brightness level of the digital brightness signal output from the A / D converter as an address, inputs the signal output frequency of each brightness level as data, and creates and stores a brightness histogram. The histogram calculation circuit reads the data in the histogram memory, calculates a parameter indicating the characteristics of the brightness histogram from this data, and outputs a control value. The limiter / adder circuit supplies the limiter level or constant addition value output from the histogram calculation circuit to the histogram memory, corrects the shape of the histogram stored in the histogram memory, and stores the corrected histogram data again in the histogram memory. The cumulative control register circuit extracts and outputs the signals of the cumulative start luminance level and the cumulative stop luminance level from the output of the histogram calculation circuit. The normalization control register circuit extracts and outputs the maximum brightness level from the output of the histogram calculation circuit. The histogram cumulative addition circuit inputs the output signal of the histogram memory and the output signal of the cumulative control register circuit, reads the corrected histogram data of the histogram memory, and cumulatively adds to calculate a cumulative histogram. The cumulative histogram memory stores the calculation result of the histogram cumulative addition circuit. The look-up table arithmetic circuit reads the data of the cumulative histogram memory and normalizes the data of the cumulative histogram memory using the output signal of the normalization control register circuit. The look-up table stores data output from the look-up table arithmetic circuit. On the other hand, the white level correction table outputs the white level correction suppression amount for suppressing the gradation correction of the luminance signal near the white level in the white direction based on the output signal of the A / D converter. Next, the correction calculation circuit
The correction signal obtained from the lookup table using the output signal of the A / D converter as an address and the correction control amount obtained from the white level correction table are used to perform a correction operation on the luminance signal output from the A / D converter. I do. By processing the luminance in this way, gradation collapse is not caused in the vicinity of the white level, and gradation correction for the entire brightness level can be effectively performed.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A gradation correction device according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing the configuration of the tone correction apparatus of this embodiment. In the figure, an A / D converter 1, a histogram memory 2, a histogram calculation circuit 3, a limiter / addition circuit 4, a cumulative control register circuit 5, a normalization control register circuit 6, a histogram cumulative addition circuit 7, a cumulative histogram memory 8, The look-up table operation circuit 9, the look-up table 10, the timing control circuit 11, and the D / A converter 14 are respectively provided as in the conventional example, and the description thereof is omitted.

The black level correction table 20 receives the output signal of the A / D converter 1 and determines the black level from the brightness level of each pixel of the video signal before correction and the correction direction thereof so as not to cause black shadow. This is a circuit that generates a correction suppression amount for gradation correction in the vicinity and outputs a suppression amount signal. The white level correction table 21 inputs the output signal of the A / D converter 1,
It is a circuit that generates a correction suppression amount for gradation correction near the white level so as not to cause whiteout and outputs the suppression amount signal from the brightness level of each pixel of the video signal before correction and the correction direction thereof. .

The correction calculation circuit 22 has a luminance signal output from the A / D converter 1, correction data obtained from the look-up table 10, black level correction suppression amount obtained from the black level correction table 20, and white level correction. This is a circuit for inputting the white level correction suppression amounts obtained from the table 21 and performing gradation correction calculation. The correction arithmetic circuit 22 is composed of, for example, multipliers 22a and 22b and an adder 22c as shown in FIG. The first multiplier 22a is a circuit that multiplies the signal of the lookup table 10 and the signal of the white level correction table 21. The second multiplier 22b is a circuit that multiplies the output of the multiplier 22a and the black level correction table 20. The adder 22c is a circuit that adds the output of the multiplier 22b and the signal of the A / D converter 1. The D / A converter 14 is a circuit that converts the digital output corrected by the correction calculation circuit 22 into an analog signal.

With respect to the tone correction apparatus of this embodiment having the above-described structure, only the operation of the portion added to the conventional example will be described. FIG. 2 is an explanatory diagram showing operation characteristics of each circuit section of the gradation correction apparatus of this embodiment. First, the data of the look-up table 10 is read using the input luminance signal digitally converted by the A / D converter 1 as an address.
Then, as shown in FIG. 2A, the gradation correction data according to the brightness level of each pixel is given to the multiplier 22a.

Next, when the correction data read from the look-up table 10 is gradation expansion data in the black direction, the black level is adjusted according to each luminance signal of the image output from the A / D converter 1. The black level correction suppression value as shown in FIG. 2B is read from the correction table 20. If the correction data read from the look-up table 10 is grayscale extension data in the white direction, the white level correction table 2 is output according to each luminance signal of the image output from the A / D converter 1.
The white level correction suppression value is read from 1 as shown in FIG. These correction data are given to the multipliers 22a and 22b and used as multiplication coefficients for correction.

That is, the correction arithmetic circuit 22 is composed of the A / D converter 1
On the basis of the brightness signal output by the above, the gradation correction data corresponding to the brightness level is read from the lookup table 10, and the black level correction suppression value output by the black level correction table 20 and the white level correction table 21 are output. Multiply by the white level correction suppression value. Then, in the adder 22c, A
A correction signal for a white or black portion is added to the uncorrected luminance level output from the / D converter 1 to generate a totally corrected luminance signal.

For example, the black levels Yb1 to Yb2 shown in FIG.
It is said that the luminance distribution of the pixels shifted to the black side as shown in the range of 1 is shifted to the white side as shown in the range of the black levels Yb3 to Yb4 shown in FIG. Make a correction. By reducing the gradation correction effect of the signal near the black level in the black direction in this way, it is possible to improve the blackout condition.

Further, as shown in the range of white levels Yw1 to Yw2 in FIG. 2A, the luminance distribution of the pixels shifted to the white side is
Depending on the white level correction suppression value, the white level Yw3 shown in FIG.
As shown in the range from to Yw4, a correction is made to shift to the black side. In this way, by reducing the gradation correction effect of the signal near the white level in the white direction, it is possible to improve the white crushing.

Finally, the D / A converter 14 converts the gradation-corrected digital brightness signal into an analog signal and outputs the brightness signal to be given to the display section. In this way, it is possible to perform gradation correction processing with a large correction effect without causing gradation collapse near the black level and near the white level.

[0036]

As described in detail above, according to the invention of claim 1 of the present application, by providing the black level correction table, the gradation of the luminance signal near the black bell is corrected in the black direction. In addition, the correction amount can be suppressed. That is, it is possible to enhance the gradation correction effect for the entire brightness level without causing gradation collapse near the black level.

Further, according to the invention of claim 3 of the present application, by providing the white level correction table, when the gradation is corrected in the white direction for the luminance signal near the white level,
The correction amount can be suppressed. That is, it is possible to enhance the gradation correction effect for the entire brightness level without causing gradation collapse near the white level.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing operation characteristics of the gradation correction device in the embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration example of a conventional gradation correction device.

FIG. 4 is an explanatory diagram (No. 1) showing operation characteristics of a conventional gradation correction device.

FIG. 5 is an explanatory view (No. 2) showing operation characteristics of the conventional gradation correction device.

[Explanation of symbols]

 1 A / D converter 2 Histogram memory 3 Histogram operation circuit 4 Limiter / adder circuit 5 Cumulative control register circuit 6 Normalization control register circuit 7 Histogram cumulative adder circuit 8 Cumulative histogram memory 9 Lookup table operation circuit 10 Lookup table 11 Timing Control circuit 14 D / A converter 20 Black level correction table 21 White level correction table 22 Correction arithmetic circuit 22a, 22b Multiplier 22c Adder

Claims (4)

[Claims] 1. An A / D converter which samples an input video signal and digitally converts a luminance signal included in the signal, and an address which is a luminance level of a digital luminance signal output from the A / D converter. A histogram memory that inputs the signal output frequency of the brightness level as data, creates and stores a brightness histogram, and the data in the histogram memory is read, the parameters showing the characteristics of the brightness histogram are calculated from this data, and the control value is output. A histogram calculation circuit, a limiter level output from the histogram calculation circuit and a constant addition value are given to the histogram memory, the shape of the histogram stored in the histogram memory is corrected, and the corrected histogram data is stored again in the histogram memory. Limiter / adder circuit to store A cumulative control register circuit that extracts and outputs signals of a cumulative start luminance level and a cumulative stop luminance level from the output of the histogram calculation circuit, and a normalization control register that extracts and outputs the maximum luminance level from the output of the histogram calculation circuit A circuit, a histogram cumulative addition circuit that inputs the output signal of the histogram memory and the output signal of the cumulative control register circuit, reads the corrected histogram data of the histogram memory, and cumulatively adds to calculate a cumulative histogram; A cumulative histogram memory that stores the calculation result of the circuit, and a routine that reads the data of the cumulative histogram memory and normalizes the data of the cumulative histogram memory using the output signal of the normalization control register circuit. An up-table arithmetic circuit, a look-up table for storing data output from the look-up table arithmetic circuit, and gradation correction of a luminance signal near a black level in the black direction based on an output signal of the A / D converter. A black level correction table for outputting a black level correction suppression amount for suppressing the above, a correction signal obtained from the lookup table using the output signal of the A / D converter as an address, and the black level correction table Based on the obtained correction control amount,
A gradation correction device, comprising: a correction calculation circuit that performs a correction calculation on a luminance signal output from the A / D converter. 2. The correction arithmetic circuit, wherein the data output from the lookup table is multiplied by a correction suppression amount output from the black level correction table, and the output of the A / D converter. 2. The gradation correction device according to claim 1, further comprising: an adder that adds the output of the first multiplier to. 3. An A / D converter that samples an input video signal and digitally converts a luminance signal included in the signal, and an address that is a luminance level of a digital luminance signal output from the A / D converter. A histogram memory that inputs the signal output frequency of the brightness level as data, creates and stores a brightness histogram, and the data in the histogram memory is read, the parameters showing the characteristics of the brightness histogram are calculated from this data, and the control value is output. A histogram calculation circuit, a limiter level output from the histogram calculation circuit and a constant addition value are given to the histogram memory, the shape of the histogram stored in the histogram memory is corrected, and the corrected histogram data is stored again in the histogram memory. Limiter / adder circuit to store A cumulative control register circuit that extracts and outputs signals of a cumulative start luminance level and a cumulative stop luminance level from the output of the histogram calculation circuit, and a normalization control register that extracts and outputs the maximum luminance level from the output of the histogram calculation circuit A circuit, a histogram cumulative addition circuit that inputs the output signal of the histogram memory and the output signal of the cumulative control register circuit, reads the corrected histogram data of the histogram memory, and cumulatively adds to calculate a cumulative histogram; A cumulative histogram memory that stores the calculation result of the circuit, and a routine that reads the data of the cumulative histogram memory and normalizes the data of the cumulative histogram memory using the output signal of the normalization control register circuit. An up-table arithmetic circuit, a look-up table for storing data output from the look-up table arithmetic circuit, and tone correction in the white direction of a luminance signal near a white level based on an output signal of the A / D converter. A white level correction table for outputting a white level correction suppression amount for suppressing the above, a correction signal obtained from the look-up table using the output signal of the A / D converter as an address, and the white level correction table Based on the obtained correction control amount,
A gradation correction device, comprising: a correction calculation circuit that performs a correction calculation on a luminance signal output from the A / D converter. 4. The correction operation circuit, a second multiplier that multiplies the data output from the lookup table by a correction suppression amount output from the white level correction table; and an output from the A / D converter. 4. The gradation correction device according to claim 3, further comprising: an adder that adds the output of the second multiplier to.