JP2000181434A - Gradation correction apparatus for video signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the effective utilization of the dynamic range of a video display device and to prevent the occurrence of black compression and white compression by executing contrast regulation according to the distribution of luminance levels, such as average luminance level and dispersion of the luminance levels. SOLUTION: The contrast regulation is executed according to the distribution of the luminance levels, such as the average luminance level and the dispersion of the luminance levels. The apparatus consists of a synchronizing signal separation circuit 1, a maximum value detection circuit 2, a minimum value detection circuit 3, a subtraction circuit 4, a divider circuit 5, a subtraction circuit 6, a multiplier circuit 7, a delay regulation circuit 8 and a synchronizing signal synthesis circuit 9. The delay regulation circuit 8 outputs the synchronizing signal D outputted from the synchronizing signal separation circuit 1 by delaying the signal for a specified time in order to synchronize the synchronizing signal D outputted from the synchronizing signal separation circuit 1 with the signal F outputted from the multiplier circuit 7. The synchronizing signal synthesis circuit 9 synthesizes the synchronizing signal outputted from the delay regulation circuit 8 and the output signal F of the multiplier circuit 7 and outputs the signal as a luminance signal G subjected to gradation correction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal gradation correcting apparatus which operates according to the distribution of luminance levels of a video signal.

[0002]

2. Description of the Related Art A conventional television signal minimum value detecting circuit is disclosed in Japanese Patent Application Laid-Open No. 56-107676. FIG. 9 shows a block diagram of a conventional video signal gradation correcting apparatus.

In FIG. 9, an input video signal SI is input to a variable correction circuit A0 whose input / output characteristics can be changed, and is supplied to an average luminance level detection circuit A4. Then, the average luminance level detection voltage is supplied to the variable correction circuit A0. The variable correction circuit A0 includes a circuit A1 whose output is the square of the input, a circuit A2 whose output is the square of the input, and an addition circuit A that adds the output of the circuit A1 and the output of the circuit A2.
3, and the addition ratio is changed according to the average luminance level.

The circuit A0 takes out the output of the circuit A1 at a rate of 1, for example, when the average luminance level is the lowest, so that the region where the information is most concentrated in the image data distribution has the highest contrast ratio. It has become.

[0005]

However, with the above configuration, it is not possible to effectively utilize the dynamic range of a video display device such as a CRT or to optimally control the black level and the white level. A phenomenon in which the gradation of a video signal having a low luminance level cannot be expressed as a whole (hereinafter, referred to as blackout) or a phenomenon in which the gradation of a video signal having a high luminance level cannot be expressed as a whole (hereinafter referred to as whiteout) Call) occurs.

[0006]

According to the present invention, there is provided a video signal gradation correcting apparatus for separating a synchronizing signal from an input luminance signal, and synchronizing the synchronizing signal with the synchronizing signal. Synchronizing signal separating means for outputting a maximum value of the synchronously separated luminance signal, maximum value detecting means for detecting the minimum value of the synchronously separated luminance signal, First subtraction means for subtracting the minimum value from a value, division means for dividing the maximum value by the output of the first subtraction means, and second means for subtracting the minimum value from the sync-separated luminance signal. Subtracting means, multiplying means for multiplying the output of the dividing means and the output of the second subtracting means, synthesizing means for synthesizing the output of the multiplying means and the synchronizing signal and outputting it as a new luminance signal. Characterized by having That.

According to the above configuration, by adjusting the contrast in accordance with the distribution of the luminance level of the video signal, the dynamic range of the video display device can be effectively utilized.
The occurrence of underexposure and underexposure can be prevented.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a block diagram of a gradation correcting apparatus for a video signal according to a first embodiment of the present invention. As shown in FIG.
A synchronization signal separation circuit 1 as a synchronization signal separation means, a maximum value detection circuit 2 as a maximum value detection means, a minimum value detection circuit 3 as a minimum value detection means, and a subtraction circuit 4 as a first subtraction means. , A dividing circuit 5 as a dividing means, a subtracting circuit 6 as a second subtracting means, a multiplying circuit 7 as a multiplying means, a delay adjusting circuit 8, and a synchronizing signal synthesizing circuit 9 as a synchronizing signal synthesizing means. Be composed.

The operation of the video signal gradation correction apparatus configured as described above will be described with reference to FIGS. Signal A, signal C, signal E, signal F, and signal G in FIG.
In, the height corresponds to the luminance level, and the pedestal level corresponds to the black level of the video.

The luminance signal A is a luminance signal from which the color difference signal has been separated in the circuit at the preceding stage, and is a signal composed of a synchronous portion where a synchronous signal exists and a video portion where video information to be displayed exists. Regarding the video information in the luminance signal A,
The maximum value is near the white level, and the minimum value is a level value somewhat higher than the pedestal level. Therefore, when such a luminance signal is displayed on the CRT, the CRT
Is not effectively utilized, and an image with a poor contrast ratio is displayed.

Therefore, the synchronization signal separation circuit 1 separates the synchronization signal D using the synchronization separation pulse B, and separates the synchronization signal D from the luminance signal from which the synchronization signal has been separated (hereinafter, referred to as the synchronization-separated luminance signal C). And outputs the synchronized signal D. The synchronization signal D is obtained by passing the luminance signal A only when the synchronization separation pulse B is at the High level, and the synchronization-separated luminance signal C is obtained only when the synchronization separation pulse B is at the Low level. Through the filter.

The maximum value detection circuit 2 detects the maximum luminance level Max1 from the signal C in one frame period or the whole one field period. The minimum value detection circuit 3 detects the minimum luminance level Min1 from the signal C in one frame period or the entire one field period. Hereafter, for simplicity, 1
A frame period or one field period is described as only one frame period. The maximum luminance level Max1 and the minimum luminance level Min1 are detected from the luminance signal in a certain one frame period, and are output during the next one frame period.

The subtraction circuit 4 subtracts the minimum luminance level Min1 output from the minimum value detection circuit 3 from the maximum luminance level Max1 output from the maximum value detection circuit 2 and outputs the result. The division circuit 5 subtracts the maximum luminance level Max1 output from the maximum value detection circuit 2 from the output value of the subtraction circuit 4 (Max1-Min1).
And output as coefficient α1. That is, the coefficient α
1 is represented by (Equation 1).

[0015]

(Equation 1)

The subtraction circuit 6 generates a luminance signal C which has been synchronized and separated.
From the minimum luminance level Min output from the minimum value detection circuit 3
1 is subtracted and output as a signal E. That is, the signal E
Is represented by (Equation 2).

[0017]

(Equation 2)

The multiplication circuit 7 multiplies the coefficient α1 output from the division circuit 5 by the output signal E of the subtraction circuit 6 and outputs the result as a signal F. That is, the signal F is represented by (Equation 3).

[0019]

(Equation 3)

The delay adjusting circuit 8 synchronizes the synchronizing signal D output from the synchronizing signal separating circuit 1 with the signal F output from the multiplying circuit 7, so that the synchronizing signal D output from the synchronizing signal separating circuit 1 is fixed. Output with time delay. The synchronizing signal synthesizing circuit 9 synthesizes the synchronizing signal output from the delay adjusting circuit 8 and the output signal F of the multiplying circuit 7 and outputs the synthesized signal as a gradation-corrected luminance signal G.

In this manner, the minimum value of the video information can be set to the black level while the maximum value of the video information at the white level remains unchanged.

FIG. 3 shows the input / output characteristics (solid line) of the luminance level of the input luminance signal and the luminance level of the luminance signal whose gradation has been corrected. For reference, the case where the gradation correction is not performed is indicated by a dotted line. That is, since the slope of the solid line is larger than that of the dotted line, the change in the luminance level is emphasized,
An image with an apparently high contrast ratio is displayed.

As described above, the dynamic range of the CRT is effectively utilized, and the occurrence of underexposure and underexposure can be prevented.

In the present embodiment, all components are configured by hardware, but all or a part of these components may be configured by software in a microcomputer. It is not limited to form. In short, it is only necessary to generate the signal F that has been subjected to gradation correction by the (Equation 4) from the luminance signal C separated in synchronization.

[0025]

(Equation 4)

(Embodiment 2) FIG. 4 is a block diagram showing a video signal gradation correcting apparatus according to a second embodiment of the present invention. 4, parts performing the same operations as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

The average luminance detection circuit 301 receives the luminance signal C separated in synchronization, and outputs the luminance signal C for one frame period.
Is detected. Conversion circuits 302, 303
Receives the average luminance level output from the average luminance detection circuit 301 and outputs a value corresponding to the average luminance level. The adjustment circuit 201 increases or decreases the value of the minimum luminance level Min1 based on the output value of the conversion circuit 302, and outputs the result as a new minimum luminance level Min2. Adjustment circuit 202
Is the maximum luminance level M based on the output value of the conversion circuit 303.
The value of ax1 is increased or decreased to obtain a new maximum luminance level Max2.
Output as The division circuit 5 calculates the maximum luminance level Max
2 is divided by the maximum luminance level Min2 and output as a coefficient α2.

In this embodiment, the average luminance detection circuit 30
1, conversion circuits 302 and 303, adjustment circuits 201 and 2
With 02, the maximum luminance level Max1 and the minimum luminance level Min1 are adjusted in accordance with the average luminance level in one frame period, and adjustment can be made to the gradation correction. For example, when the average luminance level is low, the black level is slightly raised and slightly lowered, and when the average luminance level is high, the black level is slightly lowered, so that an image that can be easily viewed by the viewer can be displayed.

The operation of this embodiment will be described below with reference to FIGS. FIG. 5 shows an example in which, in an image having a low average luminance level, the minimum luminance level is set to a value Min2 smaller than the actual value, so that the black level is slightly floated. In FIG. 5, the input / output characteristics of the luminance level of the input luminance signal and the luminance level of the luminance signal subjected to gradation correction are indicated by a solid line, the case where gradation correction is not performed is indicated by a dotted line, and the minimum luminance level and the maximum luminance level are indicated. The case of gradation correction without any adjustment is indicated by a dashed line. That is, in the present embodiment, since the solid line has a smaller inclination than the one-dot chain line, the degree of gradation correction is small.

FIG. 6 is a waveform diagram showing the operation of gradation correction having the above characteristics. 6, signals A to D are the same as the signals in FIG. In the present embodiment, since the minimum luminance level Min2 is smaller than the actual value, the signal H is a signal whose minimum value is Min1-Min2. The signal I is a signal obtained by multiplying the signal H by a coefficient α2. Since Min2 is smaller than Min1, the coefficient α
2 is smaller than the coefficient α1. The gradation corrected luminance signal J is a signal obtained by adding the synchronization signal D to the multiplied signal I.

In the present embodiment, the case where the minimum luminance level is set to a smaller value Min2 for an image having a low average luminance level has been described, but when the average luminance level is high, the minimum luminance level is set. Do the same with larger than actual. In this way, by adjusting the maximum luminance level and the minimum luminance level according to the value of the average luminance level, it is possible to display an image that is easy for the viewer to appreciate.

The same effect can be obtained even if the average luminance detection circuit 301, the conversion circuits 302 and 303, and the correction circuits 201 and 202 are constituted by software in a microcomputer.

(Embodiment 3) FIG. 7 is a block diagram showing a gradation correcting apparatus for a video signal according to a third embodiment of the present invention. 7, parts performing the same operations as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

The subtraction circuit 401 subtracts the minimum luminance level Min1 output from the minimum value detection circuit 3 from the maximum luminance level Max1 output from the maximum value detection circuit 2, and outputs the result. The conversion circuits 402 and 403 output values corresponding to the output values of the subtraction circuit 401, respectively. The adjustment circuit 201 increases or decreases the value of the minimum luminance level Min1 based on the output value of the conversion circuit 402, and outputs the result as a new minimum luminance level Min3. The adjustment circuit 202 increases or decreases the value of the maximum luminance level Max1 based on the output value of the conversion circuit 403, and outputs the result as a new minimum luminance level Max3.

In this embodiment, the maximum luminance level Max1 and the minimum luminance level Min are determined by the subtraction circuit 401, the conversion circuits 402 and 403, and the adjustment circuits 201 and 202.
The maximum luminance level Max1 and the minimum luminance level Min1 are adjusted in accordance with the difference from 1, that is, the variance of the distribution of the luminance levels in one frame period, so that it is possible to adjust the gradation correction. For example, when the luminance level distribution is dispersed, the black level is slightly lowered, and when the luminance level distribution is concentrated, the black level is slightly floated. Can be displayed.

The subtraction circuit 401 and the conversion circuit 30
The same effect can be obtained even if the components 2 and 303 are configured by software in a microcomputer.

(Embodiment 4) FIG. 8 is a block diagram showing a gradation correcting apparatus for a video signal according to a fourth embodiment of the present invention. In FIG. 8, portions performing the same operations as those in FIGS. 1, 4, and 7 are denoted by the same reference numerals, and description thereof is omitted.

The conversion circuit 501 receives the output value of the conversion circuit 302 and the output value of the conversion circuit 402, and outputs a value corresponding to the difference between the maximum luminance level Max1 and the minimum luminance level Min1, and the average luminance level. The conversion circuit 502 receives the output value of the conversion circuit 303 and the output value of the conversion circuit 403, and receives the maximum luminance level Max1 and the minimum luminance level Min1.
And outputs a value corresponding to the average luminance level.

The adjustment circuit 201 increases or decreases the value of the minimum luminance level Min1 based on the output value of the conversion circuit 501, and outputs the result as a new minimum luminance level Min4. The adjustment circuit 202 increases or decreases the value of the maximum luminance level Max1 based on the output value of the conversion circuit 502, and sets a new minimum luminance level M
ax4.

In the present embodiment, since the configuration of the second embodiment and the configuration of the third embodiment are simultaneously provided, for example, when the average luminance level is low, the black level is slightly floated and the average level is slightly reduced. When the luminance level is high, slightly lower the black level, and when the distribution of the luminance level is dispersed, slightly lower the black level, and when the distribution of the luminance level is concentrated, It is possible to simultaneously raise and slightly lower the black level, and it is possible to display an image that is more easily viewed by the viewer.

The same effect can be obtained even if the conversion circuits 501 and 502 are constituted by software in a microcomputer.

[0042]

As described above, according to the present invention, the dynamic range of the video display device can be effectively utilized by adjusting the contrast according to the distribution of the luminance levels such as the average luminance level and the variance of the luminance levels. Can be prevented, and the occurrence of underexposure and underexposure can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram of a tone correction device for a video signal according to a first embodiment of the present invention;

FIG. 2 is a waveform chart showing the operation of the video signal gradation correction device according to the first embodiment of the present invention.

FIG. 3 is a diagram showing input / output characteristics of an input luminance level and a corrected luminance level in the first embodiment.

FIG. 4 is a block diagram of a video signal gradation correction device according to a second embodiment of the present invention.

FIG. 5 is a diagram showing input / output characteristics of an input luminance level and a corrected luminance level in the second embodiment.

FIG. 6 is a waveform chart showing the operation of the video signal gradation correction device according to the second embodiment of the present invention.

FIG. 7 is a block diagram of a tone correction device for a video signal according to a third embodiment of the present invention.

FIG. 8 is a block diagram of a tone correction device for a video signal according to a fourth embodiment of the present invention.

FIG. 9 is a block diagram of a conventional video signal gradation correcting apparatus.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 synchronization signal separation circuit 2 maximum value detection circuit 3 minimum value detection circuit 4, 6, 401 subtraction circuit 5 division circuit 7 multiplication circuit 8 delay adjustment circuit 9 synchronization signal synthesis circuit 201, 202 correction circuit 301 average luminance detection circuit 302, 303 , 402, 403, 501, 502 Conversion circuit

Claims (5)

[Claims] 1. A synchronizing signal separating means for separating a synchronizing signal from an input luminance signal and outputting the synchronizing signal and a synchronizing-separated luminance signal, and detecting a maximum value of the synchronizing-separated luminance signal. Maximum value detection means, maximum value detection means for detecting the minimum value of the synchronously separated luminance signal, first subtraction means for subtracting the minimum value from the maximum value, and an output of the first subtraction means Dividing means for dividing the maximum value, second subtracting means for subtracting the minimum value from the synchronously separated luminance signal, and multiplying the output of the dividing means by the output of the second subtracting means. A gradation correcting apparatus for a video signal, comprising: multiplying means; and synthesizing means for synthesizing an output of the multiplying means and the synchronizing signal and outputting a new luminance signal. 2. In response to the sync-separated luminance signal,
2. The apparatus according to claim 1, wherein the maximum value and the minimum value are adjusted. 3. The adjustment according to claim 2, wherein the adjustment is performed based on a distribution of the luminance signal separated in synchronization.
The image signal gradation correcting device according to any one of the preceding claims. 4. The apparatus according to claim 3, wherein the adjustment is performed based on an average value of the luminance signals separated in synchronization. 5. The apparatus according to claim 3, wherein the adjustment is performed based on a difference between the maximum value and the minimum value.