JPH07131807A - Color correction device - Google Patents

Abstract

(57) [Summary] [Structure] About Step S1: Absolute value levels of the color difference signals Cb and Cr in the color image signal to be corrected,
Low saturation detection level LOW_CO set in advance
Compare LOR_LEV. About step S2:
The absolute values of the color difference signals Cb and Cr are both low saturation detection level L
When it is smaller than OW_COLOR_LEV, correction processing is performed on the color difference signal based on the luminance signal. Step S3
Regarding: Cb, Cr color correction data is written to the address of the memory device as the Cb, Cr signal conversion lookup table obtained by the above equation (1). Regarding step S4; when the absolute values of the color difference signals Cb and Cr are both higher than the low saturation detection level LOW_COLOR_LEV, color correction processing is performed using only the color difference signals. [Effect] Always good and stable color correction can be automatically performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color correction device for performing color correction of color video signals.

More specifically, the present invention relates to an apparatus for color correcting an input video signal using a look-up table.

[0003]

2. Description of the Related Art As one of conventional color correction methods, it is generally known to empirically manually correct the color of a television image.

In other words, the colors of television images are subtly different depending on the time when the images were taken, the direction and type of the camera, and so on. It will give a feeling of strangeness to the viewer. Therefore, in order to perform color correction of a television image, an operation of empirically adjusting many volumes such as gamma, pedestal, hue and gain of the image to match a desired color is performed.

On the other hand, an attempt to eliminate the empirical skill difference by automatically performing color correction instead of such manual color correction has been made on a trial basis.

That is, in the color correction apparatus using the memory device as the look-up table, Y, by the control of the memory device as the look-up table.
It has been considered to correct both the luminance signal representing the brightness of the video signal represented by Cb and Cr / the color difference signal representing the color component, the correction to the color difference signal only, or the correction to the luminance signal only.

[0007]

However, in the above-described automatic color correction using the look-up table, since correction is simultaneously performed for three axes (Y, Cb, Cr or R, G, B), it is perfect and ideal. However, the following drawbacks were observed.

Since the luminance component is affected by the color correction, the image may have a deteriorated SN ratio depending on the content of the image.

[0009] Stable color correction is not always performed, and sometimes an unfavorable color state occurs.

In the case of an image with low saturation, it may be difficult to distinguish the correction colors, and the entire screen may be color-corrected.

Therefore, in view of the above points, an object of the present invention is to provide a color correction apparatus capable of automatically executing always good and stable color correction.

[0012]

In order to achieve such an object, the present invention is directed to a color correction apparatus using a memory device as a look-up table, in which a color difference signal level representing a color component in an input video signal is lowered from a color difference signal level. It is provided with means for detecting the saturation and means for correcting only the color component by the color difference signal based on the luminance signal level representing the brightness component in the case of the low saturation.

Another aspect of the present invention comprises means for inputting a luminance signal and a color difference signal, and means for correcting the color difference signal based on the luminance signal.

[0014]

According to the above configuration of the present invention, it is possible to always automatically perform good and stable color correction.

Further, even when the saturation is low, accurate and precise color correction can be performed by adding the luminance information.

[0016]

EXAMPLES Examples of the present invention will be described in detail below.

In the present embodiment, color correction is performed on a color video signal represented by Y, Cb and Cr using a memory device as a look-up table. Lookup
As a color correction device using a memory device as a table, a three-dimensional control system is used as shown in FIG.

By simply controlling the memory device as a look-up table, not only the correction of both the luminance / color difference signal but also the correction of only the color component using only the color difference signal is performed.

In addition, performing the correction on both the luminance / color difference signals means performing the conversion operation shown in FIG. 2A in the space represented by the luminance / color difference signals.

FIG. 2B shows a waveform diagram of an actual color video signal in which both the luminance / color difference signals have been corrected.

Further, to correct only the color component using only the color difference signal means to perform the conversion operation shown in FIG. 3 (A) in the space represented by the luminance / color difference signal.

FIG. 3B shows an example of the waveform of the actual color video signal in which only the respective components are corrected by the color difference signal only.

In one embodiment of the present invention, when performing color correction for a low-saturation color, a method for controlling a memory device is used that corrects only the color component based on the color difference signal based on the luminance signal level. It is possible to distinguish between color correction at the black level and at the white level.

As a result, for example, in the actual color video signal, it is possible to perform correction such that black hair becomes slightly reddish and white clothes become slightly bluish.

That is, the so-called black balance / white balance can be easily corrected by using the memory device as the lookup table.

This cannot be realized when the correction is performed only on the color component based on only the color difference signal, because it does not depend on the luminance signal level.

In the case of correcting only the color components in the color difference signal, if the correction is applied to the low-saturation image, the entire image becomes reddish, and the black balance
It is impossible to correct the white balance.

In addition, the correction of only the color difference signal based on the luminance signal at low saturation means that the luminance /
In the space represented by the color difference signal, FIG.
Is to perform the conversion operation shown in.

FIG. 4B shows an example of the waveform of an actual color video signal in which only the color difference signal based on the luminance signal is corrected in the low saturation.

Next, in the case of correcting only the color component by the color difference signal based on the luminance signal level at the time of color correction for the low saturation color, the detection processing of the low saturation and the memory device are performed. The writing procedure is shown in FIG.

Referring to FIG. 5, the procedure of writing into the memory device as a lookup table by the three-dimensional control method will be described.

About Step S1: Absolute value levels of the color difference signals Cb and Cr in the color video signal to be corrected and the preset low saturation detection level LOW_
Compare COLOR_LEV.

Regarding step S2: Color difference signals Cb, C
Both of the absolute values of r are low saturation detection level LOW_COLOR
When it is smaller than _LEV, correction processing is performed on the color difference signal based on the luminance signal.

Luminance / in the color video signal to be corrected
Set each level of the color difference signal to Y_cor , Cb _cor , Cr_cor Tosu
It

At this time, the address of the memory device as the Cb and Cr signal conversion look-up table used for the correction process is obtained by the following equations.

[0036]

## EQU1 ## Cb_LUT_ADR = Y _cor * 2 ¹⁶ + Cb _cor * 2 ⁸ + Cr _cor Cr_LUT_ADR = Y _cor * 2 ¹⁶ + Cb _cor * 2 ⁸ + Cr _cor (1) However, the quantization in the color video signal is 8 bits, respectively. In addition, the address of the memory device as the signal conversion lookup table used for the correction process has the upper 8 bits.
Luminance signal Y, middle 8 bits color difference signal Cb, lower 8 b
It is assumed that the color difference signal Cr is input to it.

Regarding step S3: Cb and Cr color correction data are written to the addresses of the memory device as the Cb and Cr signal conversion look-up table obtained by the above equation (1).

For example, the signal levels of the color video signals to be subjected to color correction processing are represented by the luminance signal Y; 20h and the color difference signal C.
b; 01h, color difference signal Cr; 04h, corrected color difference signal Cb '; 00h, corrected color difference signal Cr'; 01h. From the equation (1), the address of the memory device as the lookup table for Cb signal conversion. At address 200104, Cb color correction data 00h is stored in the memory device address 20 as a Cr signal conversion lookup table.
The Cr color correction data 01h is written in the address 0104.

Regarding step S4: Color difference signals Cb, C
Both of the absolute values of r are low saturation detection level LOW_COLOR
When it is larger than _LEV, color correction processing is performed only by the color difference signal.

At this time, since the color correction processing is performed only by the color difference signal without depending on the luminance signal Y, the address not depending on the address by the luminance signal Y input in the memory device as the signal conversion lookup table. Write color correction data to all.

That is, for example, the respective signal levels in the color video signal to be subjected to the color correction processing are represented by the color difference signal Cb;
h, color difference signal Cr; 30h, corrected color difference signal Cb ';
20h and corrected color difference signal Cr '; E0h, the color difference signals Cb and C are independent of the luminance signal Y upper 8 bit address.
Write each color difference color correction data to the address 4030 by address of r, middle 8 bits, lower 8 bits only (*
* Is an arbitrary address).

Therefore, since the upper 8-bit address formed by the luminance signal Y input is an arbitrary address, 8 bits; 00 to FFh are set, and all 256 addresses represented by 004030 address, 014020 address, ..., FF4030 address. Write each color difference color correction data into.

As the processing procedure, in the upper 8 bit address formed by the luminance signal Y input, from the luminance signal minimum level Y _min ; 00h to the maximum level Y _max ; F.
While moving up to Fh, each color difference color correction data is repeatedly written to all addresses in the memory device as a lookup table obtained by the following equation.

[0044]

## EQU2 ## Cb_LUT_ADR = Y * 2 ¹⁶ + Cb _cor * 2 ⁸ + Cr _cor Cr_LUT_ADR = Y * 2 ¹⁶ + Cb _cor * 2 ⁸ + Cr _cor (2) However, Y; 00 to FFh.

Next, when a three-dimensional control type memory device is used as the color video signal conversion correction look-up table, the contents to be written in the memory device are shown in FIGS.

The contents of the memory device as a lookup table according to the three-dimensional control method will be described below with reference to FIGS.

Regarding FIG. 6: In the case of correcting both the luminance / color difference signals, for example, the respective signal levels in the color image signal for which the color correction processing is performed are the luminance signal Y;
40h, color difference signal Cr; 30h, corrected luminance signal Y '; 40h, corrected color difference signal Cb'; 20h, corrected color difference signal Cr '; E0h. Luminance in a memory device as a lookup table used for each color correction process. / The correction data 40h, 20h, and E0h are written in the address 204030 formed by the color difference signal input.

In the other addresses, in the case of a memory device as a look-up table for signal conversion used for the luminance signal Y, the address itself formed by the upper 8 bits of the luminance signal Y is used as write data and used for the color difference signal Cb. In the case of the memory device as the signal conversion look-up table, the address itself formed by the color difference signal Cb middle 8 bits is used as the write data, and in the case of the memory device as the signal conversion look-up table used for the color difference signal Cr, The address itself formed by the lower 8 bits of the color difference signal Cr is used as write data.

Regarding FIG. 7: In the case of correcting only the color component only by the color signal, for example, the respective signal levels in the color video signal for which the color correction processing is performed are the color difference signal Cb; 40h and the color difference signal Cr; Signal Cb '; 20h,
If the correction color difference signal Cr ′; E0h is set, it does not depend on the luminance signal input level, and therefore each color difference color is formed at the address 4030 formed by the color difference signal input in the memory device as the lookup table used for each color correction process. The correction data 20h and E0h are written (** is an arbitrary address).

In the other addresses, in the case of a memory device as a signal conversion lookup table used for the color difference signal Cb, the address itself formed by the middle 8 bits of the color difference signal Cb is used as the write data, and the color difference signal C is used.
In the case of the memory device as the signal conversion lookup table used for r, the address itself formed by the lower 8 bits of the color difference signal Cr is used as the write data.

Since the memory device as the signal conversion lookup table used for the luminance signal Y does not perform the correction process, the address itself formed by the upper 8 bits of the luminance signal Y is used as the write data at all addresses.

Regarding FIG. 8: In the case of correcting only the color difference signal based on the luminance signal in the low chroma, for example, the signal levels of the color image signals to be subjected to the color correction processing are represented by the luminance signal Y; 20h and the color difference signal Cb; 01h. , Color difference signal Cr; 0
4h, the corrected color difference signal Cb '; 00h, the corrected color difference signal Cr'; 01h, and the low saturation detection level is 8,
Since both of the color difference signal levels are lower than the low saturation detection level, the color difference signal input in the memory device as the look-up table used for each color correction process and the address 204830 formed based on the luminance signal input level, The color difference color correction data 00h and 01h are written.

In the other addresses, in the case of a memory device as a look-up table for signal conversion used for the color difference signal Cb, the address itself formed by the middle 8 bits of the color difference signal Cb is used as the write data, and the color difference signal Cb is used.
In the case of the memory device as the signal conversion lookup table used for r, the address itself formed by the lower 8 bits of the color difference signal Cr is used as the write data.

Since the memory device as the signal conversion lookup table used for the luminance signal Y does not perform the correction process, the address itself formed by the upper 8 bits of the luminance signal Y is used as the write data at all addresses.

Finally, with reference to FIG. 9, there is shown a detailed circuit configuration of a color correction device using a memory device as a lookup table by a three-dimensional control method. The contents of each block shown in this figure are as listed below.

1 is a microprocessor, 2 is a program storing ROM, 3 is a program work RAM, 4 is an address decoding circuit, 5 is a microprocessor address bus, 6 is a microprocessor data bus,
7, 16 and 25 are luminance signal Y input selector buffers,
8, 17, and 26 are color difference signal Cb input selector buffers, 9, 18 and 27 are color difference signal Cr input selector buffers, and 10 to 12 are luminance signal Y conversion look-up table memory address selector buffers. 19
21 is a lookup table for color difference signal Cb conversion
Memory address selector buffer, 28 to 30 are lookup table memories for color difference signal Cr conversion
Address selector buffer, 13 is a lookup table memory for luminance signal Y conversion, and 22 is a color difference signal C
b conversion lookup table memory, 31 is a color difference signal Cr conversion lookup table memory, 14
Is a lookup table memory for luminance signal Y conversion
Data selector buffer, 23 is a lookup table memory data selector buffer for color difference signal Cb conversion, and 32 is a lookup table for color difference signal Cr conversion.
Table memory data selector buffer, 15
Is a corrected luminance signal Y output selector buffer, 24 is a corrected color difference signal Cb output selector buffer, 33 is a corrected color difference signal Cr output selector buffer, 34 is an address decoding circuit control bus, 35 is a luminance signal Y input, 36 Is a color difference signal Cb input, 37 is a color difference signal Cr input, 38 is a corrected luminance signal Y output, 39 is a corrected color difference signal C
b output, 40 is a corrected color difference signal Cr output.

In the above-described embodiment, the color difference signal level indicating that the color has low saturation is set by controlling the memory device as a look-up table for each scene in the actual moving image. It is also possible to change.

Further, the level of the color difference signal is not necessarily limited to the case where the saturation is low, but the present invention can be applied to the case where the saturation is normal. That is, by correcting the color difference signal based on the luminance signal, it is possible to perform reliable color correction.

[0059]

As described above, according to the present invention, always good and stable color correction can be automatically performed.

[Brief description of drawings]

FIG. 1 is a diagram showing a color correction apparatus using a lookup table based on a three-dimensional control method.

FIG. 2 is an explanatory diagram showing correction of both luminance / color difference signals.

FIG. 3 is an explanatory diagram showing correction to color components only by color difference signals only.

FIG. 4 is an explanatory diagram showing correction of only a color difference signal based on a luminance signal in low saturation.

FIG. 5 is a flow chart showing a procedure for writing into a memory device as a lookup table according to a three-dimensional control method.

FIG. 6 is a diagram showing the contents of a memory device as a look-up table according to a three-dimensional control method and showing a case of correcting both luminance / color difference signals.

FIG. 7 is a diagram showing the contents of the memory device as a look-up table based on a three-dimensional control method, and showing correction of only color components based on color difference signals only.

FIG. 8 is a diagram showing the contents of the memory device as a look-up table according to a three-dimensional control method and showing correction of only color difference signals based on luminance signals at low saturation.

FIG. 9 is a block diagram showing an exemplary embodiment of the present invention in more detail.

[Explanation of symbols]

 1 Y correction LUT 2 Cb correction LUT 3 Cr correction LUT

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location // H04N 1/46 8420-5L G06F 15/66 310 4226-5C H04N 1/46 Z (72) Inventor Kiyotaka Aoki 2-2-1 Jinnan, Shibuya-ku, Tokyo Broadcasting Center of Japan Broadcasting Corporation (72) Inventor Riki Matsunaga 2-3-3 Daisaku Sakura-shi, Chiba Tomoei Sakura Research and Development Center (72) ) Inventor Tatsuro Higashi 2-16 Shimonohoro Technopark, Atsubetsu-ku, Sapporo, Hokkaido, Hokkaido, Japan In the Sapporo R & D Center (72) Inventor Masanori Wada 2-3-3 Daisaku Sakura City, Chiba Tomoe Sakura Research and Development Center Co., Ltd. Within

Claims (2)

[Claims] 1. A color correction apparatus using a memory device as a look-up table, means for detecting low saturation from a color difference signal level representing a color component in an input video signal, and the low saturation. In the case of, the color correction device is provided with means for correcting only the color component by the color difference signal based on the luminance signal level representing the brightness component. 2. A color correction apparatus comprising: a unit for inputting a luminance signal and a color difference signal; and a unit for correcting the color difference signal based on the luminance signal.