JPS6119292A - Circuit for correcting color difference matrix - Google Patents

Abstract

PURPOSE:To expand a degree of freedom of the color correction and to obtain easily a satisfactory color repeatability by supplying two color difference signals to a limiter circuit and correcting each color difference signal with the aid of the output correction signal. CONSTITUTION:A luminance signal and red signal of a narrow frequency band are assumed to be YL and R, respectively. A color difference signal (R-YL) from an input terminal 12 is supplied to a limiter circuit 21 and matrix circuit 23. From the circuit 21 an (f) signal (R-YL) is outputted. Similarly, assuming that a blue signal is B in the same manner, a color difference signal (B-YL) from an input terminal 13 is supplied to a limiter circuit 22 and matrix circuit 24. From the circuit 22 the (f) (B-YL) signal is outputted. Then outputs of the circuits 21 and 22 are supplied to the circuits 24 and 23. Assuming that c1, c2, d1 and d2 are constant, the circuits 23 and 24 output the corrected color difference signal SR-Y=C1(R-YL)+c2f(R-YL) and SB-Y=d1(B-YL)+d2f (R-YL).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a color difference matrix correction circuit suitable for use in a signal processing circuit of a color video camera.

[Prior art to the invention]

Conventionally, in color video cameras such as b+ and -t, it is common to correct the obtained color signals in order to improve color reproducibility. One way to correct this color signal is to
There is a method in which the formed color difference signals are subjected to matrix correction, and this method is called color difference matrix correction.

This color difference matrix correction is (11 Do not change white balance.

(2) Easy to measure with vector scopes, etc.9, and vector design.

It has the following advantages and is a very effective method for improving color reproducibility.

FIG. 1 is a block diagram showing an example of a signal processing circuit of a color video camera that performs IJ correction, in which 1 is an image sensor, 2 is a matrix circuit, 5.4,
5.6 is a gamma correction circuit, 7 is a matrix circuit, 8.9
10 is a subtraction circuit, 10 is a color difference matrix correction circuit, and 11 is an encoder.

In the figure, an output signal from an image sensor 1 is supplied to a matrix circuit 2, which generates a broadband luminance signal Y0 and a green signal G. , red light R8, green light B. is formed.

Each signal is supplied to gamma correction circuits 3 to 6, and gamma correction is performed so as to cancel out the gamma characteristics of the cathode ray tube of a television receiver (not shown). Generally, the gamma coefficient γ of a cathode ray tube is 2.2, so each of the above signals is processed to the 1/2.2 power. The wideband luminance signal Y obtained by gamma correction is sent to the encoder 11.
supplied to

The green signal G1 red signal R1 blue signal B obtained after gamma correction is supplied to the IJx circuit 7 to form a narrow band luminance signal YL, and this luminance signal YL is sent to the subtraction circuit 8.9.
The red signal R1 and the blue signal B are subtracted from each other to form a color difference signal (R-YL) and a color difference signal (B-YL). These color difference signals (R-YL) and (B-YL) are each corrected by a color difference matrix correction circuit 10, and the encoder 1
1. The encoder 11 combines the supplied wideband luminance signal Y and color difference signals (R-YL) and (B-YL) to obtain, for example, an NTSC color video signal.

By the way, in the color difference matrix circuit 10, a linear matrix (IJ) circuit is formed, and the corrected color difference signal CRYt) is converted into a corrected color difference signal (E-YL) by 5RYs.
) is 5n-y, the color difference matrix circuit 10 performs the process shown by the following relational expression.

5R-F"'α(R-yL)+b(B-yL)5B,=
c(E-YL)+d(R-)'L) [However, α, b, c
, d are constants] Now, if we set b = j = Q, c = 1 and change the constant cL, on the vectorscope,
As shown in Figure 2, the color reproducibility is along the (R-4) axis.
Things are changing now. Furthermore, when b = 0, α = c-1, and the constant d is changed, the color reproducibility on the vectorscope changes depending on the level of the color difference signal (B-Y), as shown in Figure 3. It varies along the (B-y) axis, but also along the (RY) axis depending on a constant d. Similarly, the color reproducibility around the (B-Y) axis can also be changed, and in the end, by selecting the constant α@b@'@'L, the most desirable color reproducibility can be obtained. can be made possible.

However, in this type of color difference matrix correction, as is clear from Figures 2 and 3, when a constant is adjusted to correct a certain hue, multiple hues always change as well. , each hue cannot be corrected independently, resulting in a low degree of freedom in color correction.

As a result, although this color signal correction method is effective for correcting specific distortions in color reproducibility due to overall characteristics including the imaging system and circuit system, in many cases it is necessary to correct for a specific color. In this case, the hue, saturation, etc. of other colors with good color reproducibility will change, and the overall color reproducibility will deteriorate on the contrary.

Therefore, with the above-mentioned conventional color difference correction circuit, it is extremely difficult to satisfactorily correct color reproduction vectors for various #i image elements and for various colors.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a color difference matrix correction circuit that eliminates the drawbacks of the prior art described above, expands the degree of freedom in color correction, and makes it possible to easily obtain good color reproducibility.

[Egg of invention]

To achieve this objective, the present invention provides a color difference signal (R-
y), (B-y) to a limiter circuit, the output signal of the limiter circuit is used as a correction signal, and the color difference signal (R-Y)
,CB-Y)'? :The feature is that it is corrected.

[Embodiments of the invention]

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

FIG. 4 is a block diagram showing an embodiment of the color difference correction circuit according to the present invention, in which reference numerals 12 and 13 are input terminals, 14 to 17 are limiter circuits, 18 is an operational amplifier circuit, and 1
9.20 is an output terminal.

In the figure, the color difference signal (R-Yt) formed in the subtraction circuit 8 (FIG. 1) is supplied from the input terminal 12 to limiter circuits 14 and 15 and an operational amplifier circuit 18, and The color difference signal (B-Y
L) is supplied from the input terminal 13 to the limiter circuits 16 and 17 and the operational amplifier circuit 1B.

The limiter circuits 14 to 17 are each set with a predetermined threshold value Vth, and the limiter circuit 14.16 clips the entire portion of the input signal below the threshold value vth, and the limiter circuit 15.1
7 clips the portion of the input signal that is equal to or higher than the threshold value vth.

For example, if the waveforms of the input signals to the limiter circuits 14 and 15 are shown in FIG.
The limiter circuit 15 outputs all the signals with the waveform shown in the figure (C1) below the threshold value Vth of the input signal.

Now, the limiter circuit 14-170 input signal 't-
The output signal of the limiter circuit 14 and 'I6 (i.e., the signal in which the input signal below the threshold Vth is clipped)
k f (, l, and the output signal t f (-1) of the limiter circuit 15.17, these output signals f (r
l.

According to this definition, the output signal of the limiter circuit 14 is f
cR-Yt), the output signal of the limit-tsuta circuit 15 is f(R
-4L), and the limiter circuit 16
The output signal of the limiter circuit 17 can be expressed as L (EYL), and the output signal of the limiter circuit 17 can be expressed as A (B-YL). These output signals, j(R-)'L), A(R-YL), L(B-Y
L) and ACBYt) are respectively supplied to the operational amplifier circuit 18. 1 operational amplifier circuit 18 performs the calculation shown in the following equation to obtain two corrected color difference signals 5p.
-re 5s-y k form.

5RY-Y=αt(R'z)+αJ(RYL>+α3a(
R-Yt)+α4(B-YL)+α5L(B'L)+α
67(E't)...(2) Sa-y=bIc
B-Yt)+h2f(B-Yr,)+bsfCBYr,
)b, (R-yL)+ to L(R-YL)+b61(R-
YL) ...... (3+ [However, a+ -% @
bl-ha is a constant] These color difference signals 5R-Y,
5R-Y is supplied to encoder 11 (FIG. 1) to form a color video signal.

In Figure 6, the threshold value Vth: 0, constant f, positive or angle, SB y = b, (Z?-1'L), 4-b2L(
This shows the change in color reproducibility when R-YL), and hue correction is performed only in the positive region of the (R-y) axis.

In FIG. 7, the threshold value vth = o, 5R-7 = α,
(R-YL)+-L(B-YL)+a61(B-YL)
5g-y=to(”L)+toz(R-yL)+ba1(R
-Yt). By changing these constants, and therefore the addition ratio, hue correction in the α, , c, and d directions can be performed independently. .

The color difference matrix correction using the fi+, +21 formula described above can further correct the saturation degree in each phase direction. Therefore, according to this embodiment, it is possible to correct color reproducibility with a high degree of freedom for various colors. It is.

FIG. 8 is an explanatory diagram showing an example of the color reproducibility of the single-tube color video camera using the above embodiment, and shows the color reproducibility on a vectorscope when Sachicon gold is used as the image sensor and a color percher image is taken. This is what I observed. Note that the reproducibility of each color is indicated by a circle.

In the same figure, 1. 5R-y=cR-YL) -〇, 15f(B-1'L)
When the hues of yellow (YE) and blue (B) are corrected as +o, 57 (B-YL), the reproducibility of each color changes in the direction shown by the arrow.

In addition, the correction of saturation in the axial direction, Kanakurame, S, Y = (R - YL) + 0.67 (R, YL) + 0.5
By performing color difference matrix correction of l-CB-YL)-o, 1s7(Z'Yr,) Ss-y=cByL)+o1a7(B-YL), color reproduction is achieved as shown in Figure 9. sex is improved.

FIG. 10 is a block diagram showing another embodiment of the color difference matrix correction circuit according to the present invention, and parts corresponding to those in FIG. 4 are given the same reference numerals.

From equation (1) shown above, the following relational expression holds between the signal f (El and 1(x)).

t (, zl= x -7<xl When this relational expression is applied to the above +21 and +81 expressions,
5s-y=a'+(R-Yt)+"J (R-Yt)+
"5CB-Yt) + bfcB YL) SB-,, b', (B-YL) + b; aCB YL)+
However, (R-YL)+h/4f(R-YL) The embodiment shown in FIG. 10 performs such arithmetic processing to perform color difference matrix correction.
limiter circuit 1 that outputs cR-Yt) and tCE-Y
z) The limiter circuit 17 that outputs k can be omitted, simplifying the circuit configuration.

FIG. 11 is a process diagram showing still another embodiment of the color difference matrix (IJ) circuit according to the present invention.
From the formula, 7<x+=x −t←) holds true, so by applying this to the above formula (21, +31), the limiter circuits 14 and 16f in FIG. 4 can be omitted.This also applies. , similar to the embodiment shown in FIG. 10, the circuit configuration can be simplified.

FIG. 11 is a block diagram showing still another embodiment of the color difference matrix correction circuit according to the present invention, in which 21.22 is a limiter circuit, 23.24 is a matrix circuit, and the parts corresponding to FIG. They are given the same code.

- In this embodiment, the color difference signal ("L) is corrected using the color difference signal (B - Yr, ) and the output signals of all limiter circuits, and the color difference signal (B1'z) t - color difference Correction was made using the signal (R-Yt) and the output signals of all limiter circuits, but depending on the color video camera,
It is not necessary to use all the obtained signals as correction signals.

The embodiment shown in FIG. 11 is a type of color video camera in which the unnecessary limiter circuit shown in FIG. 4 is omitted and the circuit configuration of the operational amplifier is simplified.

1. Let the input signals 't-- of the limiter circuits 21 and 22 be their output signals f (xl is expressed as follows.

Or, in FIG. 11, the color difference signal CR- from the input terminal 12
YL) is supplied to the limiter circuit 21 and the matrix circuit 23, and the limiter circuit 21 outputs the signal fCR-YL). Similarly, the color difference signal from the input terminal 13 (
B l'z) is the limiter circuit 22 and matrix circuit 2
4, and a signal fcBYL) is output from the limiter circuit 22. The output signal of the limiter circuit 22 is supplied to a matrix circuit 23, and the output signal of the limiter circuit 21 is supplied to a matrix circuit 24.

The matrix circuits 23 and 24 correspond to the operational amplifier circuit 18 in FIG. 4, and the matrix circuit 23 outputs a corrected color difference signal 5R-rk expressed by the following equation.

5R-y”+(7?k)+02fCB-Yt) Also,
(ma) The IJ square circuit 24 outputs a corrected color difference signal SE -Y expressed by the following equation.

5a-y=d+ (BYL)+'tfCR-Yr,) This allows hue correction in the positive or negative direction of the (R-y) axis and (B-y) axis.

In addition, this embodiment differs from the embodiment shown in FIG.
2), constant α1 in equations (3). α! , b, if all values other than Ibl+ are set to zero, or similarly, the constant α.

This corresponds to the case where everything except α6 ehl @b11 is set to zero, but as mentioned above, the limiter circuit that is not required depending on the color video camera is omitted, and the operational amplifier circuit is simplified to create a color difference matrix correction circuit. The configuration can be simplified.

[Effects of the Invention] As explained above, according to the present invention, arbitrary hue corrections can be performed independently, and the degree of freedom in hue matrix correction can be completely increased. This makes it possible to easily realize desired color reproducibility vectors, and to provide a color difference correction circuit with excellent functions while eliminating the drawbacks of the prior art described above.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an example of a signal processing circuit of a color video camera, Figures 2 and 3 are explanatory diagrams showing changes in color reproducibility due to the conventional color difference correction circuit, Figure 4 The figure is a block diagram of an embodiment of the color difference matrix correction circuit according to the present invention.
, (C) is an explanatory diagram showing the operation of each limiter circuit in FIG. 4, FIGS. 6 and 7 are explanatory diagrams showing changes in color reproducibility according to the embodiment of FIG. 4, and FIGS. Fig. 9 is an explanatory diagram showing an example of color reproducibility of a single-tube color video camera using the embodiment sound of Fig. 4, and Figs. It is a block diagram showing an example of. 10...Color difference correction circuit 12.13...
・Input terminals 14.15, 16.17...Limiter circuit 18...
Operational amplifier circuit 19.20...output terminal 21.2
2...Limiter circuit 23.21...Matrix circuit 7.7-1, sweat\, 2゜

Claims (1)

[Claims] In a color difference matrix correction circuit that corrects each of a first color difference signal and a second color difference signal to obtain desired color reproducibility, a limiter circuit receiving the first color difference signal as an input; a limiter circuit which inputs the color difference signal, and a circuit which is supplied with the first and second color difference signals and the output signals of the limiter circuits and performs arithmetic processing, The first color difference signal is corrected by adding the color difference signals and the output signals of the respective limiter circuits at a predetermined ratio, and the first color difference signal and the output signals of the respective limiter circuits are added to the second color signal. A color difference matrix correction circuit characterized in that the second color difference signal is corrected by adding output signals at a predetermined ratio.