JP2000115799A - Color correction circuit for color video image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a change in saturation of color unremarkable and to prevent false color or getting a color dark due to deficiency in a gradation expression capability at a low luminance component even in the case that a magnification rate of a luminance signal Y due to gamma correction in order to widen a dynamic range or to increase a contrast ratio of a plasma display panel PDP is made large. SOLUTION: The display device where a gamma correction circuit 12 applies gamma correction to a digital luminance signal Y, the result is outputted to a PDP, on which a color video image is displayed, is provided with a subtractor 14 that calculates a change quantity ΔY in the luminance signal Y due to the gamma correction based on an input output signal of the gamma correction circuit 12, and 1st and 2nd gain control amplifiers 22, 24 that amplify color difference signals C1, C2 at a gain in response to the obtained change quantity ΔY and provide the output to the PDP, even when the change quantity ΔY due to the gamma correction is large, a chrominance signal C is amplified at a gain in response to the change quantity ΔY so as to prevent it that the apparent saturation of color is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gamma correction circuit for gamma-correcting a digital luminance signal Y and outputting the same to a display panel, and a digital color signal C to a display panel to display a color image. The present invention relates to a color correction circuit for preventing a color quality of a display image from being degraded by gamma correction in a color video display device. The above color signal C
There are NTSC (National TV System Committee) system RY (red color difference signal) and BY (blue color difference signal) converted to digital signals and MAC (Multiple Analog Signal).
There is a signal obtained by converting U and V of the (Component) system into a digital signal. The display panel includes a PDP (Plasma Display Panel) or an LCD (Liquid Crystal Display) for displaying an image based on a digital image signal input.
There is a panel.

[0002]

2. Description of the Related Art Since a PDP has a narrower display dynamic range and a lower contrast ratio than a CRT (cathode ray tube), a gamma correction curve is set as shown by a solid line A in FIG. By increasing the rate of change, the apparent dynamic range was widened and the contrast ratio was raised. In FIG. 7, a gamma correction curve indicated by a dashed line B indicates a case where the display panel is a CRT, and a dotted line C indicates an input = output characteristic line.

[0003]

However, as shown by a gamma correction curve A shown by a solid line in FIG. 7, when the enlargement ratio of the luminance signal Y by the gamma correction is increased, the apparent color saturation changes. There was a problem. For example, FIG.
In a bright portion where the level of the luminance signal Y is larger than “128” at the center, the color looks faint, and “128” at the center.
There was a problem that the color appeared darker in smaller dark areas. In particular, in the low gradation part, there is a problem that false contours due to gradation deviation increase due to lack of gradation expression capability, resulting in a dull and dirty color.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems. Even when the enlargement ratio of the luminance signal Y by gamma correction is increased in order to widen the dynamic range or increase the contrast ratio, the change in color saturation is not affected. Is intended to make false contours and color dullness inconspicuous in low gradation portions.

[0005]

According to a first aspect of the present invention, there is provided a color correction circuit which gamma-corrects a digital luminance signal Y by a gamma correction circuit and outputs the result to a display panel, and a digital color signal C is displayed on the display panel. And a luminance change amount calculating section for calculating a change amount ΔY of a luminance signal Y by gamma correction based on an input / output signal of a gamma correction circuit, and a luminance change amount calculating section. And a gain control amplifier for amplifying the color signal C with a gain corresponding to the change amount ΔY obtained in step (1) and outputting the amplified signal to the display panel side.

The change amount .DELTA.Y of the luminance signal Y by gamma correction is calculated by the luminance change amount calculating section, and the color signal C is amplified by the gain control amplifier with a gain corresponding to the change amount .DELTA.Y. Therefore, the luminance signal Y by the gamma correction
Is large, the color signal C is amplified with a gain corresponding to the variation ΔY, so that it is possible to prevent a change in apparent color saturation. In particular, in a low gradation portion, color dullness and false contour due to lack of gradation expression ability can be made inconspicuous.

According to a second aspect of the present invention, in the first aspect of the present invention, the gain control amplifier is provided with a change amount Δ so that color correction processing can be performed in real time.
Y and the color signal C are used as addresses, and the color signal C is changed by ΔY
Is constructed by a look-up table in which data amplified with a gain corresponding to the above is stored as address contents.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the color signal is used so that it can be used for a display panel (for example, a PDP) using a digital luminance signal and color difference signal as input color video signals. C is two kinds of color difference signals C
1, C2, the gain control amplifier is composed of a first gain control amplifier and a second gain control amplifier, and the first gain control amplifier is provided with a variation ΔY
A first look-up table in which data obtained by amplifying the color difference signal C1 with a gain corresponding to the variation ΔY are stored as address contents, and
The gain control amplifier is controlled by the change amount ΔY and the color difference signal C.
2 as an address, and a second look-up table storing data obtained by amplifying the color difference signal C2 with a gain corresponding to the variation ΔY as address contents.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a color correction circuit of a color video display device according to the present invention will be described with reference to FIG.
In FIG. 1, reference numeral 10 denotes A / D (analog / digital).
The A / D converter 10 converts a luminance signal Y of an analog input color video signal into a digital luminance signal Y and outputs the converted signal. The output side of the A / D converter 10 is coupled to a gamma correction circuit 12 for performing gamma correction processing according to a gamma correction curve A in FIG. 7, and the luminance signal Y gamma-corrected by the gamma correction circuit 12 is supplied to the PDP side. Supplied to Reference numeral 14 denotes a subtractor as an example of a luminance change amount calculation unit. The subtracter 14 converts the luminance signal Y output from the A / D converter 10 from the luminance signal Y gamma-corrected by the gamma correction circuit 12. It subtracts and outputs the change amount ΔY.

Reference numerals 16 and 18 denote first and second A / D converters, respectively.
The first and second A / D converters 16 and 18 convert the color difference signals C1 and C2 of the analog input color video signals into digital color difference signals C1 and C2 and output the converted signals. 20
Is a gain control amplifier, and this gain control amplifier 20 is a first and second gain control amplifier 2
2, 24. The first gain control amplifier 22 is formed by an LUT (Look Up Table). The LUT has the change amount ΔY output from the subtractor 14 as an upper address, and the first A / D converter 1
The data which satisfies the following conditions is stored in advance as the address contents, with the color difference signal C1 output from 6 as the lower address. That is, the first A / D converter 1 has a gain corresponding to the variation ΔY output from the subtractor 14.
Data obtained by amplifying the color-difference signal C1 output from No. 6 is stored in advance. The second gain control amplifier 24
Is formed by an LUT, and the LUT includes the subtractor 14.
The change amount .DELTA.Y output from the
The color difference signal C2 output from the A / D converter 18 is used as a lower address, and data satisfying the following conditions is stored in advance as address contents. That is, the gain corresponding to the change amount ΔY output from the subtractor 14
Data obtained by amplifying the color difference signal C2 output from the A / D converter 18 is stored in advance.

Next, the operation of the embodiment of FIG. 1 will be described with reference to FIGS.
This will be described with reference to FIG. Since the change amount ΔY output from the subtractor 14 is a value obtained by subtracting the characteristic line C from the correction curve A in FIG. 7, the relationship between the digital luminance signal Y output from the A / D converter 10 and the change amount ΔY Can be represented as shown in FIG. For convenience of explanation, it is assumed that the range of the variation ΔY output from the subtractor 14 is 64 steps (6 bits) of 32 steps on the positive side and 32 steps on the negative side as shown in FIG.
ΔY = −2 of 64 steps of ΔY = −32 to +32
The data stored in the LUT of the first gain control amplifier 22 at the time of 0, -10, and +16 have the relationship represented by the solid line, the one-dot chain line, and the two-dot chain line as shown in FIG. I do. Note that, as is apparent from FIG.
0 is output from the A / D converter 10 and the gamma correction circuit 1
The level of the digital luminance signal Y input to
7 "or about" 100 ".

(A) The luminance signal Y of the input analog color video signal is converted into a digital luminance signal Y by an A / D converter 10, gamma-corrected by a gamma correction circuit 12, and supplied to the PDP side. You. This gamma correction circuit 1
In 2, the gamma correction process is performed by input / output conversion along the gamma correction curve A in FIG. The subtractor 14 converts the luminance signal Y gamma-corrected by the gamma correction circuit 12 into an A / A signal.
The luminance signal Y output from the D converter 10 is subtracted to output a change amount ΔY. For example, ΔY = −20, −10 or 1
6 is output.

(B) The color difference signals C1 and C2 of the input analog color video signals are converted into digital color difference signals C1 and C2 by first and second A / D converters 16 and 18, respectively. Second gain control amplifiers 22, 24
To enter. The first gain control amplifier 22 uses the change amount ΔY output from the subtractor 14 as an upper address,
The color difference signal C1 output from the first A / D converter 16 is used as a lower address, and data stored in advance (change amount ΔY
(Amplified data of the color difference signal C1) with a gain corresponding to The second gain control amplifier 24 is connected to the subtractor 1
4 is used as the upper address, and the change amount ΔY
The color difference signal C2 output from the / D converter 18 is used as a lower address, and data stored in advance (data obtained by amplifying the color difference signal C2 with a gain corresponding to the variation ΔY) is output.
Specifically, the first gain control amplifier 22 outputs the following data. The operation of the second gain control amplifier 24 is the same as the operation of the first gain control amplifier 22, and a description thereof will be omitted.

When .DELTA.Y = -20, the data table storing the input / output conversion data indicated by the solid line in FIG.
Data corresponding to (lower address) is output. Assuming that the color difference signal C1 is a signal having the waveform shown in FIG.
The color difference signal C amplified with a gain smaller than 1 as shown in FIG.
1 is output. That is, the signal level “3” in the negative direction smaller than the center level “128” is set to “2”.
The signal level is converted to a signal level "28" by increasing the signal level by "5", and the signal level "200" in the positive direction, which is larger than the center level "128", is decreased by "15" to a signal level "185".
Is output to the PDP side.

When .DELTA.Y = -10, .DELTA.Y is used as the upper address and the input / output conversion data indicated by the dashed line in FIG.
The stored data table is selected, and the color difference signal C
Output data corresponding to 1 (lower address) is output.
The color difference signal C1 is a signal having the waveform shown in FIG.
(Same as the signal shown in (a)), the chrominance signal amplified from the first gain control amplifier 22 with a gain smaller than 1 (greater than the above case) as shown in FIG. C1 outputs. That is, for the negative signal level “3” smaller than the center level “128”, the level is increased by “15” and converted into the signal level “18”, and the positive signal level “200” larger than the center level “128” is converted. With respect to the color difference signal C1 whose level is lowered by "7" and converted into the signal level "193", the color difference signal C1 is output to the PDP side.

When ΔY = + 16, the input / output conversion data indicated by the two-dot chain line in FIG.
The stored data table is selected, and the color difference signal C
Output data corresponding to 1 (lower address) is output.
The color difference signal C1 is a signal having the waveform shown in FIG.
(Same as the signal shown in (a)), the first gain control amplifier 22 outputs a color difference signal C1 amplified with a gain larger than 1 as shown in FIG. That is, for the negative signal level “3” smaller than the center level “128”, the level is reduced by “3” and converted to the signal level “0”, and the positive signal level “200” larger than the center level “128”. The color difference signal C1 obtained by increasing the level by "12" and converting it to the signal level "212" is output to the PDP side.

In the above-described embodiment, the color signal C is converted into two types of color difference signals C1 and C2 so that the digital luminance signal and color difference signal can be used for a display panel (for example, a PDP) that uses the input color video signal. (For example, RY, B
−Y or U, V), and the case where the gain control amplifier is composed of the first gain control amplifier and the second gain control amplifier has been described. However, the present invention is not limited to this. A video signal (for example, NTSC) is converted into a color signal separated by a YC separation circuit for separating a luminance signal Y and a color signal C, the gain control amplifier is used as a change amount ΔY and the color signal C as an address, and the color signal C is changed as a change amount ΔY The present invention can also be applied to a case where the data is amplified by a look-up table in which data amplified by a gain according to the above is stored as address contents.

In the above-described embodiment, the case where the gain control amplifier is constituted by a look-up table so that color correction processing can be performed in real time has been described. However, the present invention is not limited to this. The gain control amplifier may be any amplifier that amplifies the color signal C with a gain corresponding to the variation ΔY obtained by the luminance variation calculator and outputs the amplified signal to the display panel. For example, the gain control amplifier may be configured by an arithmetic circuit, and the arithmetic circuit may amplify the color signal C with a gain corresponding to the variation ΔY and output the amplified color signal C to the display panel.

[0019]

The color correction circuit according to the first aspect of the present invention gamma-corrects a digital luminance signal Y by a gamma correction circuit and outputs it to the display panel side, and outputs a digital color signal C to the display panel side. In a color image display device for displaying a color image, a luminance change amount calculating section for calculating a change amount ΔY of a luminance signal Y by gamma correction based on an input / output signal of a gamma correction circuit, and a luminance change amount calculating section. A gain control amplifier that amplifies the color signal C with a gain corresponding to the change amount ΔY and outputs the amplified signal to the display panel side, calculates a change amount ΔY of the luminance signal Y due to gamma correction, and responds to the change amount ΔY. Since the color signal C is amplified by the gain, even if the variation ΔY of the luminance signal Y due to the gamma correction is large, the color signal C is gained by a gain corresponding to the variation ΔY.
Can be amplified to prevent a change in apparent color saturation. In particular, in a low gradation portion, color dullness and false contour due to lack of gradation expression ability can be made inconspicuous.

According to a second aspect of the present invention, in the first aspect of the present invention, the gain control amplifier uses the change amount ΔY and the color signal C obtained by the luminance change amount calculation section as addresses and converts the color signal C into the change amount ΔY. Since the data amplified with the corresponding gain is constituted by the look-up table storing the contents of the address, the color correction processing can be performed in real time.

According to a third aspect of the present invention, in the first or second aspect, the color signal C is two kinds of color difference signals C1 and C2, and the gain control amplifier comprises a first gain control amplifier and a second gain control amplifier. The first gain control amplifier uses a first look-up table in which data obtained by amplifying the color difference signal C1 with a gain corresponding to the change amount ΔY using the change amount ΔY and the color difference signal C1 as an address and storing the data as address contents. A second look-up table in which the second gain control amplifier is configured to store the data obtained by amplifying the color difference signal C2 with a gain corresponding to the change amount ΔY as an address content, using the change amount ΔY and the color difference signal C2 as addresses. , And is used for a display panel (for example, a PDP) that uses digital luminance signals and color difference signals as input color video signals. It is possible.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a color correction circuit of a color video display device according to the present invention.

FIG. 2 is a luminance signal Y output from the A / D converter of FIG. 1;
FIG. 7 is a characteristic diagram showing a relationship between the change amount and a change amount ΔY output from a subtractor 14.

FIG. 3 shows the input / output of a data table selected by the change amount ΔY = −20, −10, +16 of the upper address among the data in the LUT constituting the first gain control amplifier 22 of FIG. FIG. 4 is a characteristic diagram illustrating conversion characteristics.

FIG. 4 is a diagram for explaining the operation of the first gain control amplifier 22 when the amount of change ΔY = −20 in FIG. 1, where (a) shows the color difference signal C1 output from the first A / D converter 16; FIG. 7B is a waveform diagram showing the color difference signal C1 output from the first gain control amplifier 22. FIG.

FIG. 5 is a diagram for explaining the operation of the first gain control amplifier 22 when the amount of change ΔY = −10 in FIG. 1, where (a) shows the color difference signal C1 output from the first A / D converter 16; FIG. 7B is a waveform diagram showing the color difference signal C1 output from the first gain control amplifier 22. FIG.

FIG. 6 is a diagram for explaining the operation of the first gain control amplifier 22 when the variation ΔY = + 16 in FIG. 1; FIG. 6 (a) is a waveform showing a color difference signal C1 output from the first A / D converter 16; FIG. 4B is a waveform diagram showing the color difference signal C1 output from the first gain control amplifier 22.

7 is a gamma characteristic curve A of the gamma correction circuit 12 in FIG.
(For PDP), B is CR shown for reference
FIG. 4 is a characteristic diagram showing a gamma characteristic curve for T, and FIG. 4C is a characteristic diagram showing an input = output characteristic line shown for reference.

[Explanation of symbols]

10: A / D converter, 12: gamma correction circuit, 14
... Subtractor (an example of a luminance change amount calculation unit) 16.
/ D converter, 18: second A / D converter, 20: gain control amplifier, 22: first gain control amplifier, 24: second gain control amplifier,
C1: first color difference signal, C2: second color difference signal, Y: luminance signal, ΔY: change amount of the luminance signal Y due to gamma correction.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (3)

[Claims] 1. A video display device for gamma-correcting a digital luminance signal Y by a gamma correction circuit and outputting the same to a display panel, and outputting a digital color signal C to the display panel to display a color image. A luminance change amount calculation unit for calculating a change amount ΔY of the luminance signal Y by gamma correction based on the input / output signal of the gamma correction circuit; and a gain corresponding to the change amount ΔY obtained by the luminance change amount calculation unit. Signal C
A gain control amplifier for amplifying the signal and outputting the amplified signal to the display panel side. 2. The gain control amplifier uses the change amount .DELTA.Y obtained by the luminance change amount calculation section and the color signal C as an address and amplifies the color signal C with a gain corresponding to the change amount .DELTA.Y. 2. The color correction circuit according to claim 1, wherein the look-up table is stored as address contents. 3. The color signal C comprises two kinds of color difference signals C1 and C2, the gain control amplifier comprises first and second gain control amplifiers, and the first gain control amplifier comprises a change amount ΔY and the color difference signal. C1 is used as an address, and a first look-up table storing data obtained by amplifying the color difference signal C1 with a gain corresponding to the change amount ΔY as address contents is provided. ΔY and the color difference signal C
2 as an address, and the color difference signal C2 as the change amount Δ
2. A second look-up table in which data amplified with a gain corresponding to Y is stored as address contents.
Or a color correction circuit of the color video display device according to 2.