JPH0578992B2 - - Google Patents

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, it is common to correct the obtained color signals in order to improve color reproducibility. One method for correcting this color signal is to perform matrix correction on the formed color difference signal, which is called color difference matrix correction.

This color difference matrix correction is (1) Do not change the white balance.

(2) Vector design is facilitated by measurements using vectorscopes, etc.

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 such color difference matrix correction, in which 1 is an image sensor, 2 is a matrix circuit, 3, 4, 5, and 6 are gamma correction circuits, and 7 1 is a matrix circuit, 8 and 9 are subtraction circuits, 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, and a wideband luminance signal Y ₀ , a green signal G ₀ , a red signal R ₀ , and a blue signal B ₀ are formed.
Each signal is supplied to gamma correction circuits 3 to 6,
Gamma correction is performed to offset 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
Since is 2.2, each of the above signals is processed to the 1/2.2 power. The gamma-corrected wideband luminance signal Y is supplied to the encoder 11.

The gamma-corrected green signal G, red signal R, and blue signal B are supplied to the matrix circuit 7 to form _a narrowband luminance signal Y _L.
are supplied to subtraction circuits 8 and 9 and subtracted from the red signal R and blue signal B, respectively, to form a color difference signal ( _RYL ) and a color difference signal (B- _YL ). These color difference signals ( _RYL ) and (B- _YL ) are each corrected by a color difference matrix correction circuit 10 and supplied to an encoder 11. In the encoder 11, the supplied wideband luminance signal Y and color difference signals (R- _YL ) and (B- _YL ) are combined to obtain, for example, an NTSC color video signal.

By the way, in the color difference matrix circuit 10, a linear matrix circuit is formed, and if the corrected color difference signal (R- _YL ) is _SRY and the corrected color difference signal (B- _YL ) is _SBY , then The color difference matrix circuit 10 performs processing expressed by the following relational expression.

S _RY = a (R-Y _L ) + b (B-Y _L ) S _BY = c (B-Y _L ) + d (R-Y _L ) [However, a, b, c, and d are constants] Now , b=d=0, and c=1, and when the constant a is changed, the color reproducibility changes along the (RY) axis on the vectorscope, as shown in FIG. Furthermore, when b = 0, a = 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 (BY) 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 by selecting constants a, b, c, and d, the most desirable color reproducibility can be obtained. It can be done.

However, in this kind 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.
It is not possible to correct each hue 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 and saturation of other colors with good color reproducibility will change, and the overall color reproducibility will deteriorate.

Therefore, with the conventional color difference matrix correction circuit described above, it is extremely difficult to satisfactorily correct color reproduction vectors for various colors and in accordance with various image sensors.

[Purpose of the invention]

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned prior art,
An object of the present invention is to provide a color difference matrix correction circuit in which the degree of freedom in color correction is expanded and good color reproducibility can be easily obtained.

[Summary of the invention]

In order to achieve this object, the present invention supplies the color difference signals (R-Y) and (B-Y) to a limiter circuit, uses the output signal of the limiter circuit as a correction signal,
The feature is that the color difference signals (R-Y) and (B-Y) are 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 matrix correction circuit according to the present invention,
3 is an input terminal, 14 to 17 are limiter circuits, 18
1 is an operational amplifier circuit, and 19 and 20 are output terminals.

In the figure, the color difference signal (R- _YL ) formed by the subtraction circuit 8 (FIG. 1) is transmitted from the input terminal 12 to the limiter circuits 14, 15 and the operational amplifier circuit 18.
The color difference signal (B-Y _L ) formed by the subtraction circuit 9 (FIG. 1) is supplied from the input terminal 13 to the limiter circuits 16 and 17 and the operational amplifier circuit 18 .

The limiter circuits 14 to 17 each have a predetermined threshold value V _th
is set, the limiter circuits 14 and 16 clip the portion of the input signal that is below the threshold value V _th , and the limiter circuits 15 and 17 clip the portion of the input signal that is above the threshold value V _th . For example, if the waveforms of the input signals to the limiter circuits 14 and 15 are shown in FIG. 5a, the limiter circuit ₁₄ outputs a signal with the waveform shown in FIG. Further, the limiter circuit 15 outputs a signal having a waveform shown in _FIG .

Now, let's talk about the input signals of limiter circuits 14 to 17.
The output signal of the limiter circuits 14 and 16 is
(i.e., the input signal threshold V_thBelow is the clip
signal) (x), limiter circuits 15, 17
If the output signal of is (x), then these output signals
Define (x) and (x) as follows. (x)=0 (x<V_th) x-V_th(xV_th) (x)=x−V_th(x<V_th) 0 (xV_th)...(1) According to this definition, the output signal of the limiter circuit 14
The number is (RY_L), output signal of limiter circuit 15
(R-Y_L) and can also be expressed as
The output signal of the Mitsuta circuit 16 is (B-Y_L), Rimi
The output signal of the vine circuit 17 is (B-Y_L) is expressed as
can be done. These output signals (RY_L),
(RY_L), (B-Y_L), (B-Y_L)teeth
The signals are respectively supplied to the operational amplifier circuit 18.

The operational amplifier circuit 18 performs the calculation shown in the following equation to form two corrected color difference signals S _RY and S _BY .

S_RY=a₁(RY_L)+a₂ (RY_L)+a₃(R
−Y_L)+a_Four(B-Y_L)+a_Five (B-Y_L)+a₆(B
−Y_L)...(2) S_BY=b₁(B-Y_L)+b₂ (B-Y_L)+b₃(B
−Y_L)b_Four(RY_L)+b_Five (RY_L)+b₆ (R-
Y_L)...(3) [However, a₁~a₆,b₁~b₆is a constant] These color difference signals S_RY,S_BYis encoder 11
(Figure 1) to form a color video signal.
be done.

Figure 6 shows the threshold V_th= 0, constant b₂Also positive
is negative, S_BY=b₁(B-Y_L)+b₂ (RY_L) This shows the change in color reproducibility when
With this correction, only the positive region of the (RY) axis
Hue correction is performed for.

Figure 7 also shows the threshold value V_th= 0, S_RY=a₁(RY_L)+a_Five (B-Y_L)+a₆(B
−Y_L) S_BY=b₁(B-Y_L)+b_Five (RY_L)+b₆(R
−Y_L) This shows the change in color reproducibility when
, changing these constants and therefore the addition ratio.
The hue correction in the a, b, c, and d directions can be performed independently by
can be done.

The color difference matrix correction using equations (1) and (2) above can further correct the degree of saturation in each phase direction. Reproducibility can be corrected.

FIG. 8 is an explanatory diagram showing an example of color reproducibility of a single-tube color video camera using the above embodiment,
This is an observation of the color reproduction on a vectorscope when capturing an image of a color birch using Sachicon as an image sensor. Note that the reproducibility of each color is indicated by a circle.

In the same figure, now, S_RY=(RY_L)−0.15(B−Y_L)+0.5 (B
−Y_L) When correcting the hue of yellow (YE) and blue (B), each
Color reproducibility changes in the direction shown by the arrow.

Also, including correction of axial saturation, S_RY=(RY_L)+0.6(RY_L)+0.5 (B
−Y_L)−0.15(B−Y_L) S_BY=(B-Y_L)+0.18 (B-Y_L) By performing color difference matrix correction of
As shown in the figure, color reproducibility is improved.

FIG. 10 is a block diagram showing another embodiment of the color difference matrix correction circuit according to the present invention.
Parts corresponding to the figures are given the same reference numerals.

From equation (1) shown earlier, the signal between (x) and (x)
The following relational expression holds true.

(x)=x−(x) Applying this relational expression to the above equations (2) and (3), we get S_RY＝a′₁(RY_L)+a′₂(RY_L)+a′₃(B
−
Y_L)+a′_Four(B-Y_L) S_BY＝b′₁(B-Y_L)+b′₂(B-Y_L)+b′₃(R
−
Y_L)+b′_Four(RY_L) However, a′₁=a₁+a₂,a′₂=a₃−a₂・ a′₃=a_Four+a_Five,a′_Four=a₆−a_Five・ b′₁=b₁+b₂,b′₂=b₃−b₂・ b′₃=b_Four+b_Five,b′_Four=b₆−b_Five The embodiment shown in FIG. 10 performs such arithmetic processing.
It performs color difference matrix correction by
So, in Figure 4 (RY_L) output limiter
circuit 15 and (B-Y_L) output limiter times
The circuit configuration can be simplified since the line 17 can be omitted.

FIG. 11 shows a color difference matrix circuit according to the present invention.
FIG. 7 is a block diagram showing still another embodiment,
From equation (1), (x)=x− (x) holds, so apply this to equations (2) and (3) above.
By doing so, the limiter circuits 14 and 16 in FIG.
This is so that it can be omitted. This is also the first
Similar to the embodiment shown in Figure 0, the circuit configuration is simplified.
can be achieved.

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 and 22 are limiter circuits, 23 and 24 are matrix circuits, and the parts corresponding to FIG. They are given the same code.

In the embodiments so far, the color difference signal ( _RYL )
is corrected using the color difference signal (B- _YL ) and the output signals of all limiter circuits, and the color difference signal (B-YL) is
Y _L ) was corrected using the color difference signal (R-Y _L ) and the output signals of all the limiter circuits, but depending on the color video camera, it is not always necessary to use all the obtained signals as correction signals. There isn't. 11th
The embodiment shown in the figure 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.

Now, the input signals of the limiter circuits 21 and 22 are
Then, their output signals (x) are expressed as follows.

(x)=0 (x<V _th ) x−V _th (xV _th ) or (x)=x−V _th (x<V _th ) 0 (xV _th ) In FIG. The color difference signal ( _RYL ) is supplied to the limiter circuit 21 and the matrix circuit 23, and the limiter circuit 21 outputs a signal ( _RYL ). Similarly, the color difference signal (B- _YL ) from the input terminal 13 is supplied to the limiter circuit 22 and the matrix circuit 24, and the limiter circuit 22 outputs the signal (B- _YL ). 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 _SRY expressed by the following equation.

_SRY = _c1 (R- _YL )+ _c2 (B- _YL ) Furthermore, the matrix circuit 24 outputs a corrected color difference signal _SBY expressed by the following equation.

S _BY = d ₁ (B-Y _L ) + d ₂ (R-Y _L ) This allows hue correction in the positive or negative direction of the (R-Y) axis and the (B-Y) axis.

Note that this embodiment is similar to the embodiment shown in FIG. 4 when all constants other than the constants a ₁ , a ₅ , b ₁ , and b ₅ in equations (2) and (3) are set to zero, or similarly, constant a ₁ ,
This corresponds to the case where all values other than a ₆ , b ₁ , and b ₆ are 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. The configuration of the color difference matrix correction circuit can be simplified.

〔Effect of the invention〕

As explained above, according to the present invention, arbitrary hue corrections can be performed independently, increasing the degree of freedom in hue matrix correction, and making it possible to perform corrections according to the color video camera. As a result, it is possible to easily realize a desired vector of good color reproducibility, and to provide a color difference matrix correction circuit with excellent functions by eliminating the drawbacks of the above-mentioned prior art.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of a signal processing circuit of a color video camera, Figs. 2 and 3 are explanatory diagrams showing changes in color reproducibility due to a conventional color difference matrix correction circuit, and Fig. 4 is a block diagram showing an example of a signal processing circuit of a color video camera. FIGS. 5a, b, and c are explanatory diagrams showing the operation of each limiter circuit in FIG. 4, and FIGS. FIGS. 8 and 9 are explanatory diagrams showing changes in color reproducibility depending on the embodiment, respectively. FIGS. 12 are block diagrams showing other embodiments of the color difference matrix correction circuit according to the present invention. 10... Color difference matrix correction circuit, 12, 13
...Input terminal, 14,15,16,17...Limiter circuit, 18...Operation amplifier circuit, 19,20...
...Output terminal, 21, 22...Limiter circuit, 2
3, 24...matrix circuit.

Claims (1)

[Claims] 1. 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; The circuit includes a limiter circuit which receives the second color difference signal as input, 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 second color difference signals and the output signals of the respective limiter circuits at a predetermined ratio, and the first color difference signals 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 the output signals of the above at a predetermined ratio.