JP2001016605A - Digital color correction circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To conduct color correction without being affected by a noise or a quantization error. SOLUTION: The digital color correction circuit is provided with a Y calculation circuit 10, color difference signal calculation circuits 12, 14, a C calculation circuit 16, a θ calculation circuit 18, a discrimination circuit 20, a LUT group 30, a LUT selection circuit 42, a correction method selection circuit 44 and an arithmetic circuit 46. Then the discrimination circuit 20 discriminates to which of a plurality of preset stages a luminance level Y, a chrominance level C and a hue θ belong, the discrimination circuit 40 discriminates whether or not color correction is applied, a corresponding LUT in the LUT group 30 is selected on the basis of a discrimination output, using the selected LUT to apply color correction to the color difference signals R-Y, B-Y, the correction method selection circuit 44 selects the correction method selection circuit 44 after the color correction or the correction method selection circuit 44 before the color correction, and the arithmetic circuit 46 calculates R, G, B, signals to obtain a color correction output. Since the digital system is adopted for the color correction, the digital color correction circuit applies the color correction to the color difference signals R-Y, B-Y without being affected by a noise or a quantization error.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit used in a color television receiver, a video tape recorder, and the like, and relates to a circuit for correcting the color of a video signal.

[0002]

2. Description of the Related Art Conventionally, this type of color correction circuit is performed in an analog system, and determines the luminance level, color level, and hue of an input composite video signal (composite video signal). When it is determined that the signal corresponds to a color, color correction is performed. Generally, this type of color correction is performed in the form of a color difference signal, because the color level and the hue are easily changed at the same time. A conventional analog color correction circuit has been used, for example, as shown in FIG. 7 or FIG. FIG. 7 shows a case where the display device 1 is a CRT (cathode ray tube), and Y / C
The separation circuit 2 separates the luminance level (luminance signal) Y and the color level (color signal) C from the input composite video signal, and the chroma decoder 3 separates the color difference signals RY, B-
The Y signal is decoded, the color correction circuit 4 performs analog color correction, the matrix circuit 5 creates analog R, G, and B signals, and supplies the analog signals to the display device 1 as they are. FIG. 8 shows a case where the display device 6 requires a digital signal such as a PDP (plasma display panel) or an LCD (liquid crystal display panel).
A luminance level (luminance signal) Y and a color level (color signal) C are separated from the input composite video signal by a Y / C separation circuit 2, and a color difference signal R−
Y and BY are decoded, the color correction circuit 4 performs analog color correction, and the matrix circuit 5 performs analog R correction.
The A, D (analog / digital) converter 7 converts the G1, B1, and B1 signals into digital R2, G2, and B2 signals and supplies them to the display device 6.

[0003]

However, in the case where the display device 1 as shown in FIG. 7 is a CRT, since the final output signal is mainly an analog signal, there is a particular problem even if color correction is performed in an analog system. However, when the display device 6 as shown in FIG. 8 requires a digital signal such as a PDP or LCD, there is little advantage in performing the color correction by the analog method, and conversely, there are the following disadvantages. . (1) Since color correction is performed with a very small amount of signal change, the effect of noise is large, and the analog method has a problem that it is weak to noise. (2) An A / D converter 7 converts a video signal color-corrected by an analog method into a digital signal, and then converts the signal into a PDP or an LCD.
Therefore, there is a problem that the quantization error at the time of the A / D conversion cannot be ignored by delicate color correction.

The present invention has been made in view of the above problems, and has as its object to provide a color correction circuit capable of performing color correction without being affected by noise or quantization errors.

[0005]

According to the present invention, a luminance level Y is calculated from input digital R, G, B signals.
A calculating circuit for calculating a color difference signal R from the R and B signals and the luminance level Y;
A color difference signal calculation circuit for calculating -Y and BY, a C calculation circuit for calculating a color level C from the color difference signals RY and BY, and a hue θ from the color difference signals RY and BY Calculation circuit, a discrimination circuit for discriminating to which of a plurality of preset levels each of the luminance level Y, the color level C and the hue θ belongs, and a color correction based on the discrimination output of the discrimination circuit. And a LUT storing input / output conversion data that satisfies a plurality of types of color correction characteristics for each input of the color difference signals RY and BY.
(Look-up table) and L based on the discrimination output of the discrimination circuit when the discrimination circuit determines that color correction is to be performed.
An LUT selection circuit for selecting a corresponding LUT from the UT group; and a color difference signal R- after color correction by the LUT selected by the LUT selection circuit, based on a determination signal from the determination circuit.
A correction method selection circuit for selecting one of the color difference signals RY and BY before color correction calculated by the color difference signal calculation circuit, and a color difference signal R selected by the correction method selection circuit;
An arithmetic circuit for calculating and outputting digital R, G, and B signals based on -Y, BY, and the luminance level Y;

A luminance level Y, color difference signals RY, BY, a color level C, and a hue θ are calculated based on the inputted R, G, B signals, and the luminance level Y, the color level C, the hue θ are calculated.
Is determined to which of a plurality of preset stages belongs, and it is determined whether or not to perform color correction based on the determination signal. A corresponding LUT is selected from the LUT group based on the determination output when it is determined that the color correction is performed, and the color difference signals RY, B are selected using the selected LUT.
-Y color correction is performed. Color-corrected color difference signal R-
One of Y, BY and the color difference signals RY, BY before color correction is selected based on a determination signal as to whether or not to perform color correction, and the selected color difference signals RY, B are selected. R, G, and B signals are calculated based on −Y and the luminance level Y and output.
As described above, color correction is performed digitally,
Color correction without the influence of noise or quantization error is performed.

In order to enable skin color correction, green color enhancement and blue color correction, the LUT group is composed of three types of LUTs for skin color correction, green color enhancement and blue color correction, and when it is determined that the color correction is performed by the determination circuit. In addition, the LUT selection circuit, based on the discrimination output of the discrimination circuit, makes the corresponding LU
Select T.

In order to enable external control of whether or not to perform color correction, an external control signal 1 for controlling whether or not to perform color correction is supplied to a correction method selection circuit from a determination signal of a determination circuit. A function to prioritize and select a correction method is added.

In order to allow a part of the plurality of types of color correction to be stopped from the outside, the LUT selection circuit determines the external control signal 2 for stopping a part of the plurality of types of color correction. A function to cut off a part of the judgment output of the circuit is added.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a digital color correction circuit according to the present invention will be described below with reference to FIG. FIG.
10 is a Y calculation circuit, 12 is a first color difference signal calculation circuit, 14 is a second color difference signal calculation circuit, 16 is a C calculation circuit,
18 is a θ calculation circuit. The Y calculation circuit 10 calculates the luminance level Y from the digital three primary color signals R (red), G (green), and B (blue) signals using the following equation (1). Y = 0.3R + 0.59G + 0.11B (1) The first color difference signal calculation circuit 12 calculates the R signal and the luminance level Y
The second color difference signal calculation circuit 14 calculates a color difference signal BY from the B signal and the luminance level Y. The C calculation circuit 16 calculates the color level C from the input color difference signals RY and BY using the following equation (2). C = {(RY) 2 + (BY) 2} (2) The θ calculation circuit 18 calculates the hue θ from the color difference signals RY and BY input using the following equation (3). Is calculated. θ = tan-1 {(RY) / (BY)} (3)

Reference numeral 20 denotes a discrimination circuit.
It comprises a discrimination circuit 22, a C discrimination circuit 24, and a θ discrimination circuit 26. The Y discriminating circuit 22 includes the Y calculating circuit 1
0, it is determined to which of a plurality of preset brightness levels the brightness level Y calculated belongs to, and the C determination circuit 24 determines the color level C calculated by the C calculation circuit 16.
Belongs to any of a plurality of preset color levels, and the θ determination circuit 26 determines whether the θ calculation circuit 18
It is determined to which of a plurality of preset hues the hue θ calculated in the above belongs. For example, the Y determination circuit 22
Is DATA = 1 when the calculated luminance level Y value is 0-19 IRE, and DATA when the calculated luminance level Y is 20-39 IRE.
= 2,..., 80 to 100 IRE, it is determined that DATA = 5. 0IRE corresponds to the black level, and 100IRE
Corresponds to the white level. Also, the color difference signals RY, BY
Is the orthogonal axis, and the color is represented by a vector centered at the intersection, the color level C corresponds to the length of the vector, and the hue θ corresponds to the phase angle of the vector with respect to the BY axis.
The C determination circuit 24 determines that the value of the calculated color level C is 0 to 9
DATA = 1 for IRE, DATA = 2 for 10-19 IRE,..., DAT for 40-49 IRE
It is determined that A = 5. The θ determination circuit 26 determines which of a plurality of levels of the phase angle the value of the calculated hue θ belongs to.

Reference numeral 30 denotes a group of LUTs.
A plurality of LUT groups 321 and 322 for the color difference signal RY;
, 32n (n is an integer of 2 or more), and a plurality of LUT groups 341, 342, ..., 34n for the color difference signal BY. The LUT groups 321-32n, 341-34
n indicates the input of each of the color difference signals RY and BY calculated by the first and second color difference signal calculation circuits 12 and 14 for skin color correction, green enhancement, and blue correction. Input / output conversion data that satisfies three types of color correction characteristics is stored.

Reference numeral 40 denotes a judgment circuit. The judgment circuit 40 judges whether or not to perform color correction based on the discrimination output of the discrimination circuit 20 (in the case of performing color correction) and "0" (in case of color correction). (When no correction is made). Reference numeral 42 denotes an LUT selection circuit. When the determination signal of the determination circuit 40 is “1”, the LUT selection circuit 42 is configured to output the LUT groups 321 to 32n and 341 to 34 based on the determination output of the determination circuit 20.
Select the corresponding LUT from n. For example, the discrimination circuit 20 determines that the luminance level Y satisfies the condition of Y ≧ Yh (set value), the color level C satisfies the condition of C ≧ Ch (set value), and the hue θ is 90 ≦ θ ≦ 1.
When 117 ° which satisfies the condition 50 and the input R, G, B signals are determined to be flesh color, the determination signal of the determination circuit 40 becomes “1”, and the LUT selection circuit 42 causes the LUT groups 321 to 32n, LUTs (for example, 321 and 341) for skin color correction are selected from 341 to 34n. The LUT selection circuit 42 further has a function of cutting off a part of the determination output of the determination circuit 20 by the external control signal 2. For example, a 2-bit external control signal 2
Accordingly, a function of interrupting a determination output for correcting a part of the three types of color correction (for example, green emphasis or green emphasis and blue correction) is provided.

Reference numeral 44 denotes a correction method selection circuit. The correction method selection circuit 44 determines that the determination signal of the determination circuit 40 is "1".
, The color difference signal R output from the LUT group 30
-Y and BY (signal after color correction) are output, and when the determination signal of the determination circuit 40 is "0", the first and second signals are output.
The color difference signal R− calculated by the color difference signal calculation circuits 12 and 14
Y and BY (signals before color correction) are output. The correction method selection circuit 44 further includes an external control signal 1 (for example, a 1-bit signal) for controlling whether or not to perform color correction.
Is given priority over the determination signal of the determination circuit 40. 46 is an arithmetic circuit, and this arithmetic circuit 46
The color difference signal R-
Based on Y, BY, and the luminance level Y calculated by the Y calculation circuit 10, R, G, and B signals are calculated and output by calculations using the following equations (4), (5), and (6). . R = (R−Y) + Y (4) G = (Y−0.3R−0.11B) /0.59 (5) B = (B−Y) + Y (6)

An embodiment in which the digital color correction circuit configured as described above is used when the display device is a PDP or LCD will be described with reference to FIG. In FIG. 2, the same parts as those in FIG. In FIG.
2 is a Y / C separation circuit, 3 is a chroma decoder, 5 is a matrix circuit, 6 is a display device composed of a PDP or LCD, 7 is an A / D converter, 9 is a digital color correction circuit according to the present invention, The Y / C separation circuit 2 separates the luminance level Y and the color level C from the input composite video signal, and the chroma decoder 3 converts the color level C into the color difference signal R-
Y and BY are decoded, analog R3, G3, and B3 signals are created by a matrix circuit 5, converted into digital R4, G4, and B4 signals by an A / D converter 7, and converted by a digital color correction circuit 9. The digital R5, G5, and B5 signals obtained by performing the color correction processing by the digital method are supplied to the display device 6. As described above, since the digital color correction circuit 9 performs the color correction processing by the digital method, it is possible to perform the color correction without the influence of the noise and the quantization error. Details will be described below.

Next, the operation of the digital color correction circuit 9 of FIG. 1 will be described with reference to FIGS. First, the process of calculating the luminance level Y, the color level C, and the hue θ and determining to which stage the calculated value belongs will be described. The luminance level Y is calculated from the input R, G, and B signals by the Y calculating circuit 10, and to which stage the luminance level Y belongs is determined by the Y determining circuit 22 in the determining circuit 20. First and second color difference signal calculation circuits 12 and 14
From the input R and B signals and the luminance level Y
−Y and BY are calculated, the color level C and the hue θ are calculated from the color difference signals RY and BY by the C calculation circuit 16 and the θ calculation circuit 18, and the C determination circuit 24 in the determination circuit 20 The .theta. determination circuit 26 determines to which stage the color level C and the hue .theta. belong.

Next, based on the discrimination signal of the discrimination circuit 20, (A) the case where the skin color is corrected, (B) the case where the green color is emphasized, (C) the case where the blue color is corrected, and (D) the case where the color correction is not performed. , (E) when the color correction is controlled by the external control signal 1,
(F) The case where color correction is controlled by the external control signal 2 will be described separately.

(A) In the case of skin color correction This correction is performed to make the color near the skin color, to which the human eye is sensitive, look like an optimal color. As shown in FIG. 4, the color difference signals RY, When the color is represented by a vector centered on the intersection with BY being the orthogonal axis, color correction is performed to shift the color to the hue (I axis) of the flesh color whose phase angle θ with respect to the BY axis is 123 °. The data processed by each circuit is a digital amount, but for convenience of explanation, the data will be described in an analog amount.
Each of the luminance level Y, the color level C, and the hue θ calculated in 2, 2, and 26 is the setting condition (Y ≧
(Yh, C ≧ Ch, 90 ° ≦ θ ≦ 150 °), it is assumed that skin color correction is performed. A digital quantity corresponding to the above-mentioned analog quantity is, for example, as follows. Y ≧ Yh, C ≧ C shown in FIG.
h, the condition of 90 ° ≦ θ ≦ 150 ° is that DATA = 3 to 5 of the discrimination circuit 22 and DATA = 2 of the discrimination circuit 24, respectively.
-4, DATA = 3-5 of the discrimination circuit 26.

When the condition shown in FIG. 3 is satisfied, a judgment signal "1" is output from the judgment circuit 40 and LU
The signals are input to the T selection circuit 42 and the correction method selection circuit 44.
When the θ determination circuit 26 determines that θ belongs to the range of 90 ° ≦ θ <123 °, the color correction characteristics 1a, 1
LUT storing input / output conversion data satisfying b and 1c
(For example, 321 and 341, 321 and 342, 322 and 3
A signal for selecting 41) is supplied from the LUT selection circuit 42 to the LUT group 30. When the θ determination circuit 26 determines that θ belongs to the range of 123 ° ≦ θ ≦ 150 °, the LUT storing the input / output conversion data satisfying the color correction characteristics 2a, 2b, and 2c is selected. The signal is supplied from the LUT selection circuit 42 to the LUT group 30.

For this reason, the LUT group 30 performs the following input / output conversion. The calculated θ is 90 ° ≦ θ <12
When it belongs to the central portion within the range of 3 °, its color correction characteristic 1b has 12 points as shown by the arrow 1b in FIG.
The color difference signal R- is adjusted so that the correction amount approaching 3 ° is maximized.
Input / output conversion is performed to slightly reduce Y and greatly reduce the color difference signal BY. In addition, the calculated θ is 9
When it belongs to both sides within the range of 0 ° ≦ θ <123 °, the color correction characteristics 1a and 1c indicate the arrow 1 in FIG.
a, as shown by 1c, 1
Input / output conversion is performed to reduce the correction amount approaching 23 °. . The calculated θ is 123 ° ≦ θ ≦ 150 °
, The color correction characteristic 2b indicates that the color correction characteristic 2b is 123 ° as shown by the arrow 2b in FIG.
The input / output conversion is performed to slightly increase the color difference signal RY and greatly increase the color difference signal BY so that the correction amount approaching to the maximum becomes maximum. In addition, the calculated θ is 123
When it belongs to both side portions within the range of ° ≦ θ ≦ 150 °, the color correction characteristics 2a and 2c show arrows 2 in FIG.
a, as shown by 2c, 1
Input / output conversion is performed to reduce the correction amount approaching 23 °. Therefore, the LUT group 30 outputs the color difference signals RY and BY that have undergone skin color correction.

Since the judgment signal "1" of the judgment circuit 40 is also inputted to the correction method selection circuit 44, the color difference signals RY and B- from the LUT group 30 whose skin color has been corrected by the correction method selection circuit 44. Y is selected and input to the arithmetic circuit 46. In the arithmetic circuit 46, the color difference signal R obtained by correcting the skin color
The R, G, and B signals are calculated based on -Y, BY, and the luminance level Y, and the R, G, and B signals that have undergone skin color correction are output.

(B) Case of Green Emphasis This correction is performed to make the image look vivid by making the green color of the leaves of the tree darker. Rather than simply enhancing green, the correction is shown in FIG. The emphasis amount is changed by the hue θ so that the peak of the emphasis is brought to the yellow-green color (hue θ ° 210 °) of the leaves of the tree, and the correction direction matches the hue direction of the input R, G, and B signals. The ratio of the color difference signals RY and BY for each correction is fixed. For convenience of explanation, each of the discriminating circuits 22 and 2 of the discriminating circuit 20
4 and 26, the calculated luminance level Y, color level C, and hue θ are respectively set to the setting conditions (Yg
1 ≦ Y ≦ Yg2, Cg1 ≦ C ≦ Cg2, 170 ° ≦ θ ≦
245 °), it is assumed that green enhancement is performed.

When the condition shown in FIG. 3 is satisfied, a determination signal "1" is output from the determination circuit 40 and the LU
The signals are input to the T selection circuit 42 and the correction method selection circuit 44.
As shown in FIG.
70 ° ≦ θ <185 °, 185 ° ≦ θ <200 °, ...,
When it is determined that the input / output conversion data satisfies the respective ranges of 230 ° ≦ θ ≦ 245 °, a signal for selecting the LUT storing the input / output conversion data satisfying the color correction characteristics 3a, 3b,. The data is supplied from the circuit 42 to the LUT group 30.

For this reason, in the LUT group 30, the following input / output conversion is performed. The calculated θ is yellow-green (hue θ ≒
210 °), the color difference signal R has a color correction characteristic 3c such that the correction amount of the color level becomes maximum as shown by an arrow 3c in FIG. Input / output conversion for reducing -Y and BY is performed. Also, the calculated θ is 185 ° away from yellow-green.
≤θ <200 °, 215 ° ≦ θ <230 °, the color correction characteristics 3b, 3d
As shown by arrows 3b and 3d, the color difference signals RY and B- so that the correction amount of the color level becomes smaller than that in the case of arrow 3c.
An input / output conversion that reduces Y is performed. Also, the calculated θ is 170 ° ≦ θ <185 ° which is further away from the yellowish green.
In the color correction characteristic 3a, the input / output for reducing only the color difference signal BY so that the correction amount of the color level becomes smaller than the case of the arrow 3b as shown by the arrow 3a in FIG. Conversion is performed. Further, when the calculated θ belongs to the range of 230 ° ≦ θ ≦ 245 ° that is further away from the yellowish green, the color correction characteristic 3e indicates that
As shown by an arrow 3e in FIG.
The color difference signals RY and BY are set to be smaller than in the case of d.
Is performed. Therefore, LU
The T group 30 outputs color difference signals RY and BY with green emphasis.

Since the judgment signal "1" of the judgment circuit 40 is also inputted to the correction method selection circuit 44, the color difference signals RY, B- Y is selected and input to the arithmetic circuit 46. The arithmetic circuit 46 calculates the R, G, and B signals based on the green-enhanced color difference signals RY and BY and the luminance level Y, and outputs green-enhanced R, G, and B signals.

(C) In the case of blue correction This correction is performed to make the whole image bright by making white bluish. As shown in FIG. 6, the input R, G and B signals are Slightly blue direction (hue θ = 34
(7.6 °). The range of the color level C to be corrected is a range in which there is no color, and the higher the color level C is, the smaller the correction amount is. Further, the ratio of the color difference signals RY and BY is fixed so that the correction direction is constant in the blue direction (hue θ = 347.6). For convenience of explanation, Y discriminating circuit 22 of discriminating circuit 20, C
Each of the luminance level Y and the color level C calculated by the discrimination circuit 24 is determined by the setting condition (Y ≧ Y) shown in FIG.
b, when it is determined that Cb1 ≦ C ≦ Cb4) is satisfied, it is assumed that blue correction is performed.

When the condition shown in FIG. 3 is satisfied, the judgment signal "1" of the judgment circuit 40 is output, and the LUT
The signals are input to the selection circuit 42 and the correction method selection circuit 44. As shown in FIG. 3, the C determination circuit 24 determines that the color level C is Cb1 ≦ C <Cb2, Cb2 ≦ C <Cb3, Cb3.
When it is determined that the input / output conversion data satisfies the respective ranges of ≦ C ≦ Cb4, a signal for selecting an LUT in which input / output conversion data satisfying the color correction characteristics 4a, 4b, and 4c is stored is:
The data is supplied from the LUT selection circuit 42 to the LUT group 30.

For this reason, the LUT group 30 performs the following input / output conversion. When the calculated color level C is relatively small and belongs to the range of Cb1 ≦ C <Cb2 (when the color density is low in a whitish image), the arrow 4a in FIG. The input / output conversion for decreasing the color difference signal RY and increasing BY is performed so that the correction amount of the color level is maximized as shown by. The calculated color level C is medium and Cb2 ≦ C <C
b3, the color correction characteristic 4b
Then, as shown by an arrow 4b in FIG. 6, input / output conversion is performed to decrease the color difference signal RY and increase BY so that the correction amount of the color level becomes medium. When the calculated color level C is large and belongs to the range of Cb3 ≦ C ≦ Cb4 (when the color is deep in a whitish image), the color correction characteristic 4c is indicated by an arrow 4c in FIG. The input / output conversion for decreasing the color difference signal RY and increasing the BY is performed so that the correction amount of the color level is minimized as shown by. Accordingly, the LUT group 30 outputs the color difference signals RY and BY corrected for blue.

Since the judgment signal "1" of the judgment circuit 40 is also inputted to the correction method selection circuit 44, the color difference signals RY, B- Y is selected and input to the arithmetic circuit 46. The arithmetic circuit 46 calculates R, G, and B signals based on the blue-corrected color difference signals RY and BY and the luminance level Y, and outputs blue-corrected R, G, and B signals.

(D) When Color Correction is Not Performed When the determination circuit 20 determines that none of the setting conditions shown in FIG. 3 is satisfied, the determination signal 40 is output from the determination circuit 40 to perform the correction method. Selection circuit 4
4 to select the color difference signals RY and BY (signals before correction) calculated by the first and second color difference signal calculation circuits 12 and 14 and output them to the arithmetic circuit 46. In the arithmetic circuit 46,
The R, G, B signals are calculated based on the color difference signals RY, BY before correction and the luminance level Y, and R, G, B signals without color correction are output.

(E) When Color Correction is Controlled by External Control Signal 1 When the external control signal 1 is "0", the external control signal 1 is ignored, and the case described in (A) to (D) above is applied. Similarly, the correction method selection circuit 44 uses the determination signals “1” and “0” of the determination circuit 40 to correct the color difference signal R−
Y, BY, and the color difference signals RY, BY before correction are selected and output. When the external control signal 1 is “1”, the correction method selection circuit 44 ignores the determination signal of the determination circuit 40 and ignores the determination signals of the first and second color difference signal calculation circuits 12 and 14, BY (signal before correction) is selected and output. Therefore, the automatic color correction can be stopped when the color correction is not desired.

(F) When Color Correction is Controlled by External Control Signal 2 When the external control signal 2 is “00”, the LUT selection circuit 42 sends an LUT selection signal corresponding to the discrimination output of the discrimination circuit 20 to the LUT group 30. And color correction similar to that described in (A) to (D) above is performed. When the external control signal 2 is "01", the discrimination output ((A)) corresponding to the skin color correction of the discrimination circuit 20 is cut off, and when the external control signal 2 is "10", the green of the discrimination circuit 20 is turned off. The discrimination output ((B)) corresponding to emphasis is cut off, and when the external control signal 2 is “11”, the discrimination output ((C)) corresponding to blue correction of the discrimination circuit 20 is cut off. Therefore, skin color correction, green enhancement,
Any one of the blue corrections can be turned off. For example, when the user does not want to emphasize green, by setting the external control signal 2 to “10”, the inputted R,
The G and B signals are in the green emphasis condition (Yg1 ≦
Y ≦ Yg2, Cg1 ≦ C ≦ Cg2, 170 ° ≦ θ ≦ 24
5 °), the corresponding discrimination output from the discrimination circuit 20 is cut off, and green emphasis is not performed. When the external control signal 2 is "10", the input R,
If the G and B signals satisfy the setting conditions shown in and / or in FIG. 3, flesh color correction and / or blue enhancement are performed.

In the embodiment of FIG. 1, it is possible to externally control whether or not to perform color correction (for example, to prevent color correction when it is inconvenient in automatic color correction). 2), the case where a function of selecting a correction method by giving priority to the external control signal 1 over the determination signal of the determination circuit is added to the correction method selection circuit has been described. However, the present invention is not limited to this. The present invention can also be used when the control of whether or not to perform the color correction based on the signal 1 is omitted.

In the embodiment of FIG. 1, a function of cutting off a part of the discrimination output based on the external control signal 2 is added to the LUT selection circuit, so that skin color correction, green emphasis,
Although one of the three types of color correction of blue correction can be stopped, the present invention is not limited to this, and three types of skin color correction, green enhancement, and blue correction can be performed using a 3-bit external control signal 2. Any of the two types of color correction that can be stopped can be used, or those that do not have a function of cutting off a part of the determination output by the external control signal 2 can be used. it can.

In the embodiment shown in FIG. 1, the case where the LUT group is composed of three types of LUTs for skin color correction, green enhancement and blue correction has been described. However, the present invention is not limited to this. A case in which a plurality of LUTs corresponding to any one or two of skin color correction, green enhancement, and blue correction are used, and LUTs for other color correction are added to these LUTs
It can also be used in the case of a configuration with a UT added.

[0036]

The digital color correction circuit according to the present invention has
Y calculation circuit, color difference signal calculation circuit, C calculation circuit, θ calculation circuit, determination circuit, determination circuit, LUT group, LUT selection circuit,
A correction method selection circuit and an arithmetic circuit, which determines whether the calculated luminance level Y, color level C, and hue θ belong to any of a plurality of preset levels, and performs color correction based on the determination signal And selecting a corresponding LUT from the LUT group based on the determination output when it is determined that the color correction is to be performed, and using the selected LUT to determine the color of the color difference signals RY and BY. After performing the correction, one of the color difference signals RY and BY after the color correction and the color difference signals RY and BY before the color correction is selected based on a determination signal as to whether or not to perform the color correction. The R, G, and B signals were calculated based on the color difference signals RY, BY and the luminance level Y to obtain a color correction output. As described above, in the present invention, since the color correction is performed by the digital method, it is possible to perform the color correction free from the influence of the noise and the quantization error.

The LUT group includes three types of LUTs for skin color correction, green color enhancement, and blue color correction. When the LUT selection circuit determines that the color correction is performed by the determination circuit, three types of LUTs are provided based on the determination output of the determination circuit. Corresponding LUT of LUT
Is selected, skin color correction, green enhancement, and blue correction can be performed.

If the correction method selection circuit is provided with a function of selecting the correction method by giving priority to the external control signal 1 for controlling whether or not to perform color correction over the determination signal of the determination circuit, Whether or not to perform the correction can be externally controlled. For example, it can be controlled from outside so that the color correction is not performed when the automatic color correction is inconvenient.

If the LUT selection circuit is provided with a function of cutting off a part of the discrimination output with the external control signal 2 for stopping a part of the plurality of types of color correction, Some of them can be stopped. For example, if the user does not want to emphasize green, the external control signal 2 may be a signal for turning off green emphasis, thereby performing color correction (for example, skin color correction) in which green emphasis is stopped.
When it is not desired to perform green enhancement and blue correction, the external control signal 2 is a signal for turning off green enhancement and blue correction, thereby performing color correction (only skin color correction) in which green enhancement and blue correction are stopped. Can be.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing an embodiment in which the digital color correction circuit of FIG. 1 is used when the display device is a PDP or LCD.

FIG. 3 is a diagram for explaining the operation of FIG. 1;

FIG. 4 is a diagram for explaining the operation of the skin color correction of FIG. 1;

FIG. 5 is a diagram for explaining the effect of green emphasis in FIG. 1;

FIG. 6 is a diagram for explaining the operation of the blue color correction of FIG. 1;

FIG. 7 is a block diagram showing a conventional example in which an analog color correction circuit is used when a display device is a CRT.

FIG. 8 is a block diagram showing a conventional example in which an analog color correction circuit is used when a display device is a PDP or LCD.

[Explanation of symbols]

6 ... Display device composed of PDP or LCD 7 ...
A / D converter, 9 ... Digital color correction circuit in one embodiment of the present invention, 10 ... Y calculation circuit, 12 ... First
A color difference signal calculation circuit, 14... A second color difference signal calculation circuit,
16 ... C calculating circuit, 18 ... θ calculating circuit, 20 ... discriminating circuit, 22 ... Y discriminating circuit, 24 ... C discriminating circuit, 2
6 ... θ discriminating circuit, 30 ... LUT group, 321-32
n: RUT group for RY, 341 to 34n ... LUT group for BY, 40 ... Judgment circuit, 42 ... LUT selection circuit, 44 ... Correction method selection circuit, 46 ... Operation circuit, C
... Color level, Y ... Luminance level, θ ... Hue, R-
Y, BY: a color difference signal.

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] September 1, 2000 (2009.1)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction contents]

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a digital color correction circuit according to the present invention will be described below with reference to FIG. FIG.
10 is a Y calculation circuit, 12 is a first color difference signal calculation circuit, 14 is a second color difference signal calculation circuit, 16 is a C calculation circuit,
18 is a θ calculation circuit. The Y calculation circuit 10 calculates the luminance level Y from the digital three primary color signals R (red), G (green), and B (blue) signals using the following equation (1). Y = 0.3R + 0.59G + 0.11B (1) The first color difference signal calculation circuit 12 calculates the R signal and the luminance level Y
The second color difference signal calculation circuit 14 calculates a color difference signal BY from the B signal and the luminance level Y. The C calculation circuit 16 calculates the color level C from the input color difference signals RY and BY using the following equation (2). C = {(RY) ² + (BY) ² } (2) The θ calculation circuit 18 calculates the hue from the color difference signals RY and BY input using the following equation (3). Calculate θ. θ = tan ⁻¹ {(RY) / (BY)} (3)

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction contents]

Reference numeral 30 denotes a group of LUTs.
A plurality of LUT groups 32 ₁ , 32 ₂ , for the color difference signal RY,
.., 32 _n (n is an integer of 2 or more) and a plurality of LUT groups 34 ₁ , 34 ₂ ,..., 34 _n for the color difference signal BY. The LUT groups 32 _{1 to} 32 _n , 34 _{1 to} 34
_n indicates the input of each of the color difference signals RY and BY calculated by the first and second color difference signal calculation circuits 12 and 14 for skin color correction, green enhancement, and blue correction. Input / output conversion data that satisfies three types of color correction characteristics is stored.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction contents]

Reference numeral 40 denotes a judgment circuit. The judgment circuit 40 judges whether or not to perform color correction based on the discrimination output of the discrimination circuit 20 (in the case of performing color correction) and "0" (in case of color correction). (When no correction is made). Reference numeral 42 denotes an LUT selection circuit. When the determination signal of the determination circuit 40 is “1”, the LUT selection circuit 42 is based on the determination output of the determination circuit 20 and the LUT groups 32 _{1 to} 32 _n , 34 _1. ~ 34
Select the corresponding LUT from _n . For example, the discrimination circuit 20 determines that the luminance level Y satisfies the condition of Y ≧ Yh (set value), the color level C satisfies the condition of C ≧ Ch (set value), and the hue θ is 90 ≦ θ ≦ 1.
When 117 ° that satisfies the condition 50 and the input R, G, and B signals are determined to be flesh color, the determination signal of the determination circuit 40 becomes “1”, and the LUT selection circuit 42 sets the LUT groups 32 _{1 to} 32 _{1. n} , and LUTs (for example, 32 ₁ and 34 ₁ ) for skin color correction are selected from among 34 _{1 to} 34 _n . The LUT selection circuit 42 further has a function of cutting off a part of the determination output of the determination circuit 20 by the external control signal 2. For example, a 2-bit external control signal 2
Accordingly, a function of interrupting a determination output for correcting a part of the three types of color correction (for example, green emphasis or green emphasis and blue correction) is provided.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction contents]

When the condition shown in FIG. 3 is satisfied, a judgment signal "1" is output from the judgment circuit 40 and LU
The signals are input to the T selection circuit 42 and the correction method selection circuit 44.
When the θ determination circuit 26 determines that θ belongs to the range of 90 ° ≦ θ <123 °, the color correction characteristics 1a, 1
LUT storing input / output conversion data satisfying b and 1c
(For example, 32 ₁ and 34 ₁ , 32 ₁ and 34 ₂ , 32 ₂ and 3
A signal for selecting 4 ₁ ) is supplied from the LUT selection circuit 42 to the LUT group 30. When the θ determination circuit 26 determines that θ belongs to the range of 123 ° ≦ θ ≦ 150 °, the LUT storing the input / output conversion data satisfying the color correction characteristics 2a, 2b, and 2c is selected. The signal is supplied from the LUT selection circuit 42 to the LUT group 30.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0022

[Correction method] Change

[Correction contents]

(B) Case of Green Emphasis This correction is performed to make the image look vivid by making the green color of the leaves of the tree darker. Rather than simply enhancing green, the correction is shown in FIG. The emphasis amount is changed by the hue θ so that the peak of the emphasis is brought to the yellow-green color (hue θ ° 210 °) of the leaves of the tree, and the correction direction matches the hue direction of the input R, G, and B signals. The ratio of the color difference signals RY and BY for each correction is fixed. For convenience of explanation, each of the discriminating circuits 22 and 2 of the discriminating circuit 20
4 and 26, the calculated luminance level Y, color level C, and hue θ are respectively set to the setting conditions (Yg
₁ ≦ Y ≦ Yg ₂ , Cg ₁ ≦ C ≦ Cg ₂ , 170 ° ≦ θ ≦
245 °), it is assumed that green enhancement is performed.

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction contents]

(C) In the case of blue correction This correction is performed to make the whole image bright by making white bluish. As shown in FIG. 6, the input R, G and B signals are Slightly blue direction (hue θ = 34
(7.6 °). The range of the color level C to be corrected is a range in which there is no color, and the higher the color level C is, the smaller the correction amount is. Further, the ratio of the color difference signals RY and BY is fixed so that the correction direction is constant in the blue direction (hue θ = 347.6). For convenience of explanation, Y discriminating circuit 22 of discriminating circuit 20, C
Each of the luminance level Y and the color level C calculated by the discrimination circuit 24 is determined by the setting condition (Y ≧ Y) shown in FIG.
b, when it is determined that Cb ₁ ≦ C ≦ Cb ₄ ) is satisfied, it is assumed that blue correction is performed.

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0027

[Correction method] Change

[Correction contents]

When the condition shown in FIG. 3 is satisfied, the judgment signal "1" of the judgment circuit 40 is output, and the LUT
The signals are input to the selection circuit 42 and the correction method selection circuit 44. As shown in FIG. 3, the color level C is determined by the C determination circuit 24 as Cb ₁ ≦ C <Cb ₂ , Cb ₂ ≦ C <Cb ₃ , Cb _3.
When it is belonging and the discrimination in each of the range of ≦ C ≦ Cb _4, the color correction characteristics 4a, 4b, signal for input-output conversion data to select a LUT stored satisfying 4c is,
The data is supplied from the LUT selection circuit 42 to the LUT group 30.

[Procedure amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction contents]

For this reason, the LUT group 30 performs the following input / output conversion. When the calculated color level C is relatively small and belongs to the range of Cb ₁ ≦ C <Cb ₂ (when the color density is light in a whitish image), the color correction characteristic 4a is as shown in FIG. As shown by the arrow 4a, input / output conversion is performed to decrease the color difference signal RY and increase BY in order to maximize the correction amount of the color level. The calculated color level C is medium and Cb ₂ ≦ C <C
b ₃ , the color correction characteristics 4 b
Then, as shown by an arrow 4b in FIG. 6, input / output conversion is performed to decrease the color difference signal RY and increase BY so that the correction amount of the color level becomes medium. Further, when the calculated color level C is large and belongs to the range of Cb ₃ ≦ C ≦ Cb ₄ (when the color density is deep in a whitish image), the color correction characteristic 4c is as shown in FIG. As shown by the arrow 4c, input / output conversion is performed to decrease the color difference signal RY and increase BY to minimize the color level correction amount. Accordingly, the LUT group 30 outputs the color difference signals RY and BY corrected for blue.

[Procedure amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0032

[Correction method] Change

[Correction contents]

(F) When Color Correction is Controlled by External Control Signal 2 When the external control signal 2 is “00”, the LUT selection circuit 42 sends an LUT selection signal corresponding to the discrimination output of the discrimination circuit 20 to the LUT group 30. And color correction similar to that described in (A) to (D) above is performed. When the external control signal 2 is "01", the discrimination output ((A)) corresponding to the skin color correction of the discrimination circuit 20 is cut off, and when the external control signal 2 is "10", the green of the discrimination circuit 20 is turned off. The discrimination output ((B)) corresponding to emphasis is cut off, and when the external control signal 2 is “11”, the discrimination output ((C)) corresponding to blue correction of the discrimination circuit 20 is cut off. Therefore, skin color correction, green enhancement,
Any one of the blue corrections can be turned off. For example, when the user does not want to emphasize green, by setting the external control signal 2 to “10”, the inputted R,
When the G and B signals are in the green emphasis condition (Yg ₁ ≦
Y ≦ Yg ₂ , Cg ₁ ≦ C ≦ Cg ₂ , 170 ° ≦ θ ≦ 24
5 °), the corresponding discrimination output from the discrimination circuit 20 is cut off, and green emphasis is not performed. When the external control signal 2 is "10", the input R,
If the G and B signals satisfy the setting conditions shown in and / or in FIG. 3, flesh color correction and / or blue enhancement are performed.

[Procedure amendment 10]

[Document name to be amended] Statement

[Correction target item name] Explanation of sign

[Correction method] Change

[Correction contents]

[Explanation of Reference Symbols] 6 ... Display device composed of PDP or LCD 7 ...
A / D converter, 9 ... Digital color correction circuit in one embodiment of the present invention, 10 ... Y calculation circuit, 12 ... First
A color difference signal calculation circuit, 14... A second color difference signal calculation circuit,
16 ... C calculating circuit, 18 ... θ calculating circuit, 20 ... discriminating circuit, 22 ... Y discriminating circuit, 24 ... C discriminating circuit, 2
6... Θ discrimination circuit, 30... LUT group, 32 _{1 to} 32
_n LUT group for RY, 34 _{1 to} 34 _n LUT group for BY, 40 judgment circuit, 42 LUT selection circuit, 44 correction method selection circuit, 46 arithmetic circuit, C
... Color level, Y ... Luminance level, θ ... Hue, R-
Y, BY: a color difference signal.

Claims (5)

[Claims] 1. A Y calculation circuit for calculating a luminance level Y from inputted digital R, G, B signals, and a color difference signal RY, BY from the R, B signals and the luminance level Y. A color difference signal calculation circuit, and the color difference signals RY and BY;
A C calculation circuit for calculating a color level C from the color difference signals RY and BY, and a θ calculation circuit for calculating a hue θ from the color difference signals RY and BY. Each of the luminance level Y, the color level C and the hue θ is preset. A discrimination circuit for discriminating which of the plurality of steps belongs to, a discrimination circuit for determining whether or not to perform color correction based on a discrimination output of the discrimination circuit;
A group of LUTs (look-up tables) storing input / output conversion data satisfying a plurality of types of color correction characteristics for each of the Y and BY inputs, and when the determination circuit determines that color correction is to be performed. An LU for selecting a corresponding LUT from the LUT group based on the discrimination output of the discrimination circuit
A color difference signal RY, BY after color correction by the LUT selected by the LUT selection circuit and a color calculated by the color difference signal calculation circuit based on a T selection circuit and a determination signal from the determination circuit; A correction method selection circuit for selecting one of the color difference signals RY and BY before correction; and a digital signal based on the color difference signals RY and BY selected by the correction method selection circuit and the luminance level Y. And a calculation circuit for calculating and outputting the R, G, and B signals. 2. The LUT group includes three types of LUTs for skin color correction, green color enhancement, and blue color correction, and an LUT selection circuit outputs a determination output of the determination circuit when the determination circuit determines that color correction is to be performed. 2. The digital color correction circuit according to claim 1, wherein a corresponding LUT is selected from the three types of LUTs based on the LUT. 3. The correction method selecting circuit selects the correction method by giving priority to an external control signal 1 for controlling whether or not to perform color correction over a determination signal of a determination circuit. Digital color correction circuit as described. 4. The LUT selection circuit according to claim 1, wherein a part of the discrimination output of the discrimination circuit is cut off by an external control signal for stopping a part of the plurality of types of color correction. Digital color correction circuit. 5. The digital color system according to claim 3, wherein the LUT selection circuit cuts off a part of the discrimination output of the discrimination circuit by an external control signal 2 for stopping a part of the plurality of types of color correction. Correction circuit.