JP2001184016A - Gamma correction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that, in the conventional gamma correction device, a ROM is used for a gamma table, the dot rate deciding the resolution of a picture is limited by the readout time of the ROM thereby making the device unsuitable for a high-definition display in which high speed is needed and to solve the problem that the fluctuation of brightness of the screen is generated when gamma data are changed over and appears as the flicker of the screen thereby making the screen hard to see. SOLUTION: This gamma correction device is provided with a luminance signal detecting means for temporally integrating the luminance signal level of an input video signal, a gamma correction data storage means for outputting gamma correction data on the basis of an output signal from the luminance signal detecting means and a table for gamma correction which is constituted of a storage means operating at a speed higher than that of the gamma correction data storage means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a video display device, and more particularly to a gamma correction circuit for correcting input / output characteristics in an image display device such as a liquid crystal display.

[0002]

2. Description of the Related Art For example, in a video display device such as a liquid crystal display, there are the following conventional examples regarding a gamma correction circuit for properly reproducing input / output non-linear characteristics of a device and a gradation of a video.

For example, according to Japanese Patent Laid-Open No. 7-38778, the average luminance level of a video input signal during a predetermined period is set to AD.
The converter converts the data into m-bit selection data, which is input to the gamma correction ROM, while the input luminance signal is converted into n-bit video digital data by the AD converter and input to the gamma correction ROM. The input luminance signal is corrected by gamma data according to the average value and output.

[0004] When the average value is low (when the image is dark), the low level of the input signal is raised and output, and when the average value is high (when the image is bright), the high level of the input signal is reproduced. This is an invention in which the image is output with good quality, and as a result, the gradation reproducibility is improved both in a dark portion and a bright portion of the image.

[0005]

However, in the above-mentioned invention, since the ROM is used for the gamma table, the dot rate that determines the resolution of the image is determined by the ROM.
It is not suitable for a display that requires a high-definition display that requires a high speed and is limited by the reading time of the display. Further, a change in the brightness of the screen, which occurs when the gamma data is switched, appears as a screen flicker, resulting in a screen that is very difficult to see. Further, it does not mention what gamma data should be used when transitioning from a dark screen to a bright screen, and it is very difficult to create a gamma curve as shown in the above invention. Have a problem.

The present invention has been made in view of such a situation, and is applicable to a high-definition display. Further, even when gamma data is switched by an input signal, the flicker is reduced, and an optimum gamma data is obtained. Is provided.

[0007]

Means for Solving the Problems The present invention has taken the following means in order to solve the above problems.

That is, the gamma correction device according to the first means includes a luminance signal detecting means for temporally integrating a luminance signal level of an input video signal, and a plurality of gamma correction data stored therein. A gamma correction data storage unit that outputs gamma correction data based on an output signal; and a gamma correction table that performs gamma correction of an input video signal based on an output signal from the gamma correction data storage unit. The gamma correction table includes a storage unit that operates at a higher speed than the gamma correction data storage unit.

In the gamma correction device according to the second means, in the gamma correction device according to the first means, the time for integrating the luminance signal level in the luminance signal detecting means is at least 0.3 seconds or more. .

The gamma correction device according to the third means is the gamma correction device according to the first and second means, wherein the gamma correction data stored in the gamma correction data storage means is connected to the gamma correction device. An inverse function of data obtained by normalizing the characteristics of the applied voltage versus the output luminance of the display between the white level voltage and the black level voltage is defined as basic gamma data, and the basic gamma data is represented by (VTG
x, VTGy), VTGx is raised to the power of 1 / n, and VTGx raised to the power of 1 / n is denoted as VTG_Nx, and the ratio of crushing the black side when a white image is displayed on the entire screen is B.
, VTG_Nx · (1-B / 100) + B /
100 was obtained.

Further, the gamma correction device according to the fourth means is the gamma correction device according to the third means, wherein the gamma correction data stored in the gamma correction data storage means is converted to a gamma correction data corresponding to a standard gray scale signal. When the data is standard gamma, the gamma correction data selected for a dark screen is dark gamma, and the gamma correction data selected for a bright screen is light gamma, the coefficient n is continuously changed from dark gamma to standard gamma. , And from the standard gamma to the bright gamma can be obtained by simultaneously changing the coefficient n and the coefficient B.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an outline of the present invention will be described.

According to the present invention, the luminance signal is input to an AD converter via an integrating circuit including a time constant circuit to detect the level of the input luminance signal and use the signal as a switching signal for gamma data. Address.

At this time, a means for detecting a luminance signal with a time constant circuit for a relatively long time so as to detect a gradual change in luminance with respect to a sudden change in brightness of the screen is used. As a result, it was possible to suppress a change in screen brightness and flickering when gamma data was switched.

Further, continuous gamma data is written into a ROM, and a gamma table corresponding to an actual video is represented by S
RAM was used. As a result, it has become possible to cope with high-definition display requiring high speed.

Gamma data is created by the following procedure.

Whether the display is a liquid crystal display or a CRT, it is necessary to first measure the characteristic (VT characteristic) of the applied voltage-output luminance specific to the display.

Output luminance characteristics are measured while applying voltages to the device at equal intervals between a white voltage and a black voltage.

This data is normalized between the white voltage and the black voltage, and the horizontal axis (input) and the vertical axis (output) are 0 for black and 1 for white.
VT characteristic data that is monotonically increasing is generated.

The inverse function of the normalized VT characteristic is the basic gamma of this display, which corrects the VT characteristic.

The horizontal axis data of the normalized VT characteristic data is VT
When X and the vertical axis data are VTY, the basic gamma data VTGx (input) and VTGy (output) are represented by VTGx ← VTY VTGy ← VTX (Equation 1).

When the basic gamma correction is used, the output luminance changes linearly with respect to the input signal. However, in the case of a linear luminance output characteristic, an image generally becomes a white image, and an image with reduced contrast.

By making the output luminance change convex downward, the entire screen is tightened and the contrast feeling is improved.
The gamma data is corrected so that the output luminance has an nth power curve. This is hereinafter referred to as n-th power correction, and to achieve this, the input side of the gamma curve is set to 1 / n power.
Therefore, the gamma data VTG_N including the n-th power correction is VTG_Nx ← (VTGx) ^{1 / n} VTG_Ny ← VTGy (Equation 2).

Further, when a white image is displayed on the entire screen, the contrast of the image can be increased by crushing the black side. This is referred to as black cut correction, and the black cut correction of B% complies with Equation 3. The final gamma data GAM including the black cut is GAMx ← VTG_Nx · (1-B / 100) + B / 1
00GAMy ← VTG_Ny (Equation 3) The gamma data created as described above is linearly interpolated,
Alternatively, gamma data is created by spline interpolation.

In the present invention, in order to provide an image corresponding to an image signal from a case where the average value of the image luminance signal is low to a case where the average value is high, the image luminance signal has n pieces of continuously changing gamma data.

The n pieces of gamma data are created by the following algorithm.

Gamma data in the darkest image signal is hereinafter referred to as dark gamma, and gamma data in the brightest image signal is hereinafter referred to as bright gamma.

From the dark gamma to the kth one, the coefficient n of the n-th power correction is continuously changed.

The k-th node is referred to as an inflection point, and a screen (IT pattern, gray scale, etc.) to be evaluated is selected as the inflection point, and standard gamma data is set.

This enables rich gradation reproduction even on a dark screen.

From the inflection point to the bright gamma, black cut correction and n-th power correction are performed, and the black cut coefficient B and the n-th power correction coefficient n are continuously changed.

The nth power coefficient of the bright gamma is set so that the luminance change curve due to the inflection point gamma and the luminance change curve due to the bright gamma substantially coincide with each other except for the black side.

As a result, the gamma is switched only by the signal on the black side, and the flicker at the time of the gamma switching can be suppressed.

Next, an example of an embodiment of the gamma correction circuit according to the present invention will be described below with reference to FIGS.

FIG. 1 shows an example of the configuration of an embodiment of a gamma correction circuit according to the present invention, which comprises an input luminance signal detecting means 10 and a gamma data switching means 11.

FIG. 2 shows a gamma data ROM 11 of the present invention.
3 is a diagram showing a data storage state of No. 3;

The input luminance signal detecting means 10 shown in FIG. 1 comprises an integrating circuit 101 including a time constant circuit and an AD converter 102 for gamma selection.

In an ordinary integrating circuit, the brightness of the input luminance signal is integrated into a constant value corresponding to the luminance signal. In other words, when the image is dark, the integral value shows a low value,
A bright image shows a high value. Naturally, in the case of a luminance signal in which the change in brightness changes rapidly, the integrated value also changes rapidly with the change.

Switching gamma data means that
Even if the signal has the same input level, its output value changes depending on the gamma data, which means that the brightness of the screen changes.

For example, when there is a window corresponding to an input signal of 50% at the center of the screen, and the periphery of the window rapidly changes from black to white, the brightness of a portion corresponding to the input 50% is: The integrated value changes depending on the surrounding brightness, and the selected gamma table also changes, so that the brightness varies. At this time, the fluctuation of the brightness around the window portion moves in conjunction with the fluctuation of the brightness of the window portion, and as a result, the brightness of the portion that should be constant appears to flicker. In the case of the integrating circuit 101 including the time constant circuit of this embodiment, the integrating circuit has a time constant of about 0.3 to 0.5 seconds. That is, even if the brightness around the window fluctuates rapidly, a gradual change can be obtained as an integral value.

In the case of a normal display, one vertical period forming a screen is 1/60 second.

That is, the screen is rewritten every 1/60 second, and a human recognizes a screen such as a moving image by continuously viewing the screen, but it takes about 0.3 to 0.5 seconds. Is equivalent to the time of about 20 to 30 images on the screen. By giving this time constant, even if the brightness around the window fluctuates rapidly, the gamma data is switched slowly, and the brightness of the window also fluctuates slowly, so that the window part appears to flicker. It became possible to hold down.

The input luminance signal detecting means 10 comprises an A / D converter 102 for converting the integrated value of the luminance signal thus obtained into a gamma data selection signal.

The gamma data switching means 11 in FIG.
A data input converted to digital data of the detected luminance signal, a counter circuit 111, a write address generation circuit 112, a gamma ROM 113 storing gamma data created based on a gamma data creation procedure described later, and SRAMs 114, 115, and 116 for each color serving as a gamma table, and a switch 117,
118 and 119.

In the embodiment of the present invention, as shown in FIG. 2, there are 64 types of gamma data to be switched corresponding to the luminance signal, and the luminance signal is digital data of 1024 gradations. The signal passed through the integration circuit is set to the upper bits via the 6-bit AD converter 102, and an address for selecting a gamma table for each of 1024 gradations is created by the counter circuit 111, and the address is generated as the lower bits to generate a write address. The signal is input to the circuit 112.

Now, in the vertical blanking period, the switches 117, 118 and 119 are switched to the gamma ROM 113 by the SW switching signal generated by the write address generation circuit 112.

Thereafter, the 6-bit upper address corresponding to the luminance signal from the luminance signal detecting means 10 at that time and the 1024 lower addresses corresponding to black to white of the screen generated by the counter circuit 111 are used for the gamma ROM 1.
13 is selected, and the RGB data separated into three primary colors are stored in SRAMs 114, 115, and 1 respectively.
16 is written.

When the vertical blanking period ends, the SW
117, SW118 and SW119 are switched to the video signal data side, and the video data to be displayed is stored in the SRAM 11
4, 115, 116,
M114, 115, and 116 output gamma table data according to the address.

FIG. 3 shows continuous gamma data obtained by applying the gamma generation method of claim 3 to a liquid crystal display. A solid line a indicates gamma data (dark gamma) on the darkest screen, and a dotted line b indicates gamma at a nodal point. The data, dashed line c indicates gamma data (bright gamma) on the brightest screen.

The gamma has 64 levels of gamma data from dark gamma to bright gamma, and the inflection point is the thirteenth, counting from the dark gamma to which the gray scale signal applies. FIG. 4 is data obtained by normalizing the VT characteristics between the black and white voltages of a general liquid crystal display, and the inverse function thereof is the basic gamma data FIG.

Based on the basic gamma data of FIG. 5, continuous gamma data of 64 gradations is created as follows by changing the n-th power coefficient and the black cut coefficient.

[0052]

[Table 1] From the dark gamma to the inflection point gamma, the n-th coefficient is continuously changed from n = 1 to 1.35, and from the inflection point gamma to the bright gamma, the n-th coefficient is changed from n = 1.35 to 1. At the same time, the black cut coefficient B was continuously changed from 0% to 20%.

FIG. 3 shows gamma data created by the above procedure, and FIG. 6 shows a change in output luminance on the display when the continuous gamma data is used.

In FIG. 6, a solid line a indicates a luminance output curve using dark gamma, a dotted line b indicates a luminance output curve when using the inflection point gamma, and a dashed line c indicates a luminance output curve when using bright gamma.

In a dark scene, the luminance change is represented by the solid line a, so that the gradation reproduction on the black side is good. In a bright scene, the luminance change is indicated by the dashed line c, so that the gradation expression on the white side is good, and the black side is cut. Therefore, an image having a sense of contrast is obtained.

The n-th power coefficient in the bright gamma is selected such that the change in the luminance output on the white side of the one-dot chain line c substantially coincides with the dotted line b, thereby minimizing screen flicker at the time of gamma switching. Was.

The above-described creation of gamma data is as follows.
Of course, it is also possible to realize it by software.

[0058]

According to the present invention described above, the following effects can be obtained.

Since the gamma correction circuit device according to the first aspect of the present invention has the above-described configuration, the output of gamma data corresponding to an image depends on the reading speed of the SRAM. Generally, the reading speed of the SRAM is about five times as fast as that of the ROM, and this makes it possible to cope with a high-definition display requiring a high reading speed.

Since the gamma correction circuit according to the second aspect of the present invention has the above-described configuration, it is possible to reduce the flickering of the brightness of the screen which is likely to occur when the gamma data is switched.

Since the gamma correction circuit according to the third and fourth aspects of the present invention has the above-described configuration, it is possible to minimize the flickering of the screen and to minimize the flickering of the screen as well as the circuit configuration of the second aspect. , The reproducibility of the black gradation was increased, and the overall black area was widened on a bright screen, resulting in a higher screen contrast and an easy-to-view screen with no overexposure.

The gamma data can be easily created by changing the three parameters of the n-th coefficient that determines the gradient of the gamma data and the inflection point and the ratio of black cut. Since it is possible, it is possible to easily perform gamma correction optimal for all kinds of signal media such as the type of input video signal, for example, current television broadcast, high-vision broadcast, and personal computer signal.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing one embodiment of a gamma correction circuit according to the present invention.

FIG. 2 is a diagram showing an arrangement of gamma data according to the present invention.

FIG. 3 is a graph of continuous gamma data according to the present invention.

FIG. 4 is a normalized graph of VT characteristics of a general liquid crystal.

FIG. 5 is a gamma curve for correcting VT characteristics of a general liquid crystal.

FIG. 6 is an input-output luminance characteristic subjected to continuous gamma correction according to the present invention.

[Explanation of symbols]

 Reference Signs List 10 luminance signal detecting means 101 integrating circuit 102 AD converter 11 gamma data switching means 111 counter circuit 112 write address generating circuit 113 gamma ROM 114 R-gamma table SRAM 115 G-gamma table SRAM 116 B-gamma table SRAM 117 R Address changeover switch 118 G address changeover switch 119 B address changeover switch

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazuhiro Inoko 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka F-term (reference) 5C006 AA01 AF13 AF46 AF61 AF81 BF08 BF22 BF28 BF38 FA23 5C021 PA78 PA82 PA85 XA34 5C058 AA06 BA13 BB04 BB14 5C080 AA10 BB05 DD04 DD06 EE28 JJ02 JJ05

Claims (4)

[Claims] 1. A luminance signal detecting means for temporally integrating a luminance signal level of an input video signal, a plurality of gamma correction data being stored, and outputting gamma correction data based on an output signal from the luminance signal detecting means. A gamma correction data storage unit for performing gamma correction of an input video signal based on an output signal from the gamma correction data storage unit, wherein the gamma correction table includes the gamma correction table. A gamma correction device comprising a storage unit that operates faster than the data storage unit. 2. The gamma correction apparatus according to claim 1, wherein a time for integrating the luminance signal level in said luminance signal detecting means is at least 0.3 seconds or more. 3. The gamma correction data stored in the gamma correction data storage means, wherein a characteristic of an applied voltage vs. output luminance unique to a display connected to the gamma correction device is normalized between a white level voltage and a black level voltage. If the inverse function of the converted data is basic gamma data and the basic gamma data is (VTGx, VTGy), VTGx is raised to the 1 / nth power, and VTGx raised to the 1 / nth power is set as VTG_Nx.
3. The method according to claim 1, wherein when a white image is displayed on the entire screen and a ratio of crushing the black side is B, the calculation is performed as follows: VTG_Nx · (1−B / 100) + B / 100. The gamma correction device according to item 1. 4. The gamma correction data stored in the gamma correction data storage means is a gamma correction data corresponding to a standard gray scale signal as a standard gamma, a gamma correction data selected at the time of a dark screen is a dark gamma, When the gamma correction data selected for a bright screen is bright gamma, the coefficient n is continuously changed from dark gamma to standard gamma, and the coefficient n is changed from standard gamma to bright gamma.
4. The gamma correction device according to claim 3, wherein the gamma correction device is obtained by simultaneously changing the coefficient B.