JPH02218285A - Video signal processing circuit - Google Patents

Abstract

PURPOSE:To improve the frequency characteristic and the S/N and to attain high picture quality by using a 2nd and 3rd coefficient circuits for multiplying an optional gain with a color difference signal via a low pass filter, adding output signals of 1st, 2nd and 3rd coefficient circuits and extracting the result as a luminance signal. CONSTITUTION:A matrix circuit 6 being a color difference signal circuit generates a luminance signal YL in which the constitution ratio with respect to primary color signals R,G,B is 0.30:0.59:0.11 to generate a color difference signal (R-YL) being the subtraction of the luminance signal YL from the red primary color signal R and a color difference signal (B-YL) being the subtraction of the luminance signal YL from the red primary color signal B. The color difference signal (R-YL) from the matrix circuit 6 is multiplied by a multiple of beta at a coefficient circuit 11 via an LPF 10, and the color difference signal (B-YL) is multiplied by a multiple of gamma at a coefficient circuit 13 via an LPF 12 and the result is fed to an adder 9. A high frequency luminance signal Y is extracted from the output terminal 14 as Y=0.33YH. Since the luminance signal Y is obtained from the luminance signal YH not affected between picture elements of each color, the resolution of the picture is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a video signal processing circuit used in a color video camera.

(Prior art) An RG as shown in FIG. 4(a) in which red, green, and blue are alternately arranged for an image sensor such as a charge-coupled device (COD)
In a configuration in which color separation is performed using a B-stripe filter, if the frequency of the drive signal shown in FIG. 1(b) for driving the image sensor 1 is SHO, the signal obtained from the image sensor 1 is The frequency band is 1/
Becomes 2 SHO. On the other hand, since each color has a period of 3 pixels in the horizontal direction, the frequency of the sampling pulse for color separation is 1/3S)-1o, and the signal band obtained for each color is 1/6SHO. For this reason, if the primary color signal obtained by color separation is halled to form an M-degree signal, the band will be only 1/3 of the original resolution of the number of pixels of @image element 1. This results in deterioration of horizontal resolution. In addition, Fig. 4 (C) to (e)
The pulse signals shown in FIG. 1 are sampling pulses for performing 10-color separation on the image sensor, and the frequencies SH1, SH2, and SH3 of each pulse signal are equal to 1/3 SHO.

By the way, in the NTSC television standard system, if the three primary color signals of red, green, and blue are R, G, and B, the composition ratio of the luminance signal to the primary color signal is R: G: B = 0.
．． 30:0.59:0.11 to determine color reproducibility. Further, the frequency band of the color signal is set to about 500.

From this, it can be seen that the frequency band of the luminance signal (low frequency side luminance signal Y-) consisting of the above-mentioned composition ratio should be about 500kHz. ) has nothing to do with color reproducibility, so it is conceivable to take advantage of the resolution that the image sensor 1 itself has, regardless of the above-mentioned composition ratio.

In this method, the previous sampling pulses SH1 to S
The luminance signal Y■ is obtained by adding the three primary color signals R1G and B separated by H3 without holding them. Since the luminance signal YH obtained by this method is not affected by the effects between pixels, it is possible to obtain a resolution apparently equivalent to that of the signal sampled by SHO. However, since each color filter has a different light transmittance, it is necessary to control the gain so that R:G:B=1:1:1 when the platinum surface is imaged.

FIG. 5 shows each of the signals R, G, 8. The frequency bands of Y1 and YH are illustrated respectively.

Next, a conventionally known circuit configuration for obtaining the luminance signals Y1 and Yl will be explained based on FIG. 6.

In this figure, the image sensor 1 is driven at the SHO driving frequency.
The output signals are supplied to the sampling circuit 2.3.4, sampled by sampling pulses SH1 to SH3, and separated into three primary color signals of RlG and B.

Each primary color signal R, G, B output from the sampling circuit 2.3.4 is sent to the luminance signal circuit 5B and the matrix circuit 26.
are supplied respectively. The luminance signal circuit 5B generates a luminance signal Y in which the composition ratio of the primary color signals R, G, and B is 1:1:1.
H is created. On the other hand, in the matrix circuit 26, the composition ratio of each of the primary color signals RSG and B is set to 0.30 by the hold circuit.
:0.59:0.11 is generated, and two color difference signals (R-Y), (
The color difference signals (R-YL), (B-YL 〉) are supplied to a low-pass filter (LPF) 10.12, and each color signal obtained from an output terminal 15.16 is modulated. sent to the vessel.

The luminance signals YH and YL from the luminance signal circuit 5B and the matrix circuit 26 are supplied to a subtracter 27 to produce a difference signal (YL
-YH) is produced. This difference signal is passed through a low-pass filter (LPF) of about 500kHz, which is the same as that of the color difference signal.
After passing through 28, it is supplied to an adder 29.

In the adder 29, the difference signal (YL-Yl) that has passed through the LPF 28 is added to the luminance signal Y1 supplied via the delay circuit 7, and the luminance signal Y is extracted from the output legitimate child 30.

In this video signal processing circuit, the adder 2
The luminance signal Y, which is the output of
,)=Y.

Therefore, the lower frequency side luminance signal YL is extracted as is. In addition, in the high frequency component, the difference signal (YL-yH) passing through the LPF 28 becomes O, so the luminance signal Y becomes Y=YH+ (YL-Yl) = YH, which is the luminance that is not influenced by the pixels of each color. Signal YH can be obtained and image resolution can be improved.

(Problems to be Solved by the Invention) In the conventional video signal processing circuit configured as described above, when obtaining a difference signal by the subtraction circuit 27, it is necessary to match the delay time between the luminance signal YH and the luminance signal YL. . This is because the matrix circuit 26 generally has a complicated circuit configuration, and the luminance signal Y is delayed compared to the luminance signal Y1.

However, the delay circuit for time adjustment is
If the number of pixels of the image sensor 1 is increased, providing the filter in the area B will lead to a decrease in frequency characteristics and a deterioration in the S/N ratio.

Furthermore, if the luminance signals Y1 and YL are not time-aligned accurately, a shift component will occur in the difference signal when the luminance changes. This affects the luminance signal Y and causes deterioration of image quality.

Furthermore, the same L used for the color difference signal is used for the difference signal.
There is a problem in that it is necessary to prepare a PF28, and the circuit scale also increases. Further, this LPF 28 needs to match the characteristics with those of the color difference signal, and is also subject to restrictions in terms of circuit characteristics.

The present invention was proposed to solve these problems, and provides a video signal processing circuit that can improve frequency characteristics and S/N ratio, achieve high image quality, and simplify the circuit. The purpose is to provide.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the video signal processing circuit according to the present invention adds each primary color signal obtained by imaging at an equal ratio to generate a luminance signal YH. A brightness signal generation circuit that produces a brightness signal YH output from this brightness signal generation circuit
a first coefficient circuit that multiplies by an arbitrary gain α;
The composition ratio of green and blue primary color signals R, G and B is R:G
:B=0.30 : 0.59 : 0.11 Using the luminance signal YL, the color difference signal (R-YL''), (B-Y
a color difference signal generation circuit that generates the color difference signal L); a second coefficient circuit that multiplies the color difference signal (R-YL) output from the color difference signal generation circuit by an arbitrary gain β via a low-pass filter; An arbitrary gain γ is applied to the color difference signal (B-YL) output from the signal generation circuit through a low-pass filter.
and an adder that adds together the respective output signals of the first, second, and third coefficient circuits, and the output of the adder is taken out as a luminance signal Y. Features.

(Operation) According to the above-described configuration, the luminance signal Y taken out as the output of the adder becomes Y=αYH+β(R-YL)+γ(B-YL). Here, by appropriately setting the coefficients α, β, and γ of the first, second, and third coefficient circuits, the luminance signal Y in the low frequency range can be adjusted to Y=0.3OR+0.59.
It can be extracted as G+0.11B.

On the other hand, in the high-frequency range, the low-pass filter
Since the two color difference signals (RYl) and (B-YL) both become O, the luminance signal Y becomes Y=αY■. Here, since the luminance signal YH is obtained by adding equal amounts of each primary color signal, the resolution of the image can be improved without being affected by the pixels of each color of the image sensor.

(Example) Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a video signal processing circuit according to the present invention.

In this figure, the output signal from the image sensor 1 driven by a drive signal of frequency SHO is transmitted to a sampling circuit 2.3 to which sampling pulses SH1 to SH3 are input.
．． 4, the three primary color signals R and GSB are separated and extracted.

Each primary color signal R, G from sampling circuit 2.3.4,
B is supplied to the luminance signal circuit 5A and the matrix circuit 6, respectively, and the luminance signal circuit 5A outputs primary color signals R, G,
A luminance signal YH with a composition ratio of 1:]:1 to B is produced. The luminance signal YH output from the luminance signal circuit 5A is
After passing through the delay circuit 7, the signal is multiplied by α in the coefficient circuit 8 and supplied to the adder 9.

In the matrix circuit 6 which is a color difference signal circuit, the primary color signal R
, G, B composition ratio is 0.30:0159:0.1
1, and create a color difference signal (RY) by subtracting this brightness signal YL from the red primary color signal R, and a color difference signal (B-YL) by subtracting the brightness signal YL from the blue primary color signal B. produce. The color difference signal (R-YL') from the matrix circuit 6 passes through LPFlo, is multiplied by eight in the coefficient circuit 11, and is supplied to the adder 9. Further, the color difference signal (BYl) passes through the LPF 12, is multiplied by 1 in the coefficient circuit 13, and is supplied to the adder 9.

Here, the respective coefficients α, β, and γ in the coefficient circuits 8.11.13 will be explained.

The brightness signal Y obtained by adding the respective output signals of the coefficient circuits 8, 11, and 13 in the adder 9 is as follows: Y=αYH+β(R-YL)+γ(B-Y[)...( 1) Go.

Regarding the high frequency component, R-Y at LPFlo, 12
Since L-B-Y[=0, the above luminance signal Y becomes Y=αY■.

Regarding the low frequency component, upper i[l! ￥i degree signal Y as Y=O
Considering that it is extracted as 13OR+0.59G+0.11B, by substituting YH=R1G1B YL=0.3OR+0.59G+0.11B into equation (1), Y=0.3OR+0.59G+0.11B=α (R1G
10B>10β(R(0,3OR+0.59G+0.11B>)+
γ(B − (0,3OR+0.59G+0.11B>
)-(α+β-o, 30β-0,3(>γ)R0(α
−〇859β−0.59γ)G +(α−0,11β10γ−〇,11γ)B...(2)
becomes. From this equation (2), for the red primary color signal R, 0.30-α+β-0.30β-0.30γ...(3
) For the green primary color signal G, 0.59-α-〇, 59β-〇, 59γ... (4) For the blue primary color signal B, 0, 11 = a-0, 11β + 7--0.11γ・(5
) is obtained. From these equations (3), (4), and (5), the coefficients α, β, and
As γ, we obtain α−0,33 β−−0,16 γ=−0,27.

In this way, the output signals via the respective coefficient circuits 8, 11, and 13 in which the coefficients α, β, and γ are determined are added by the adder 9, so that the output terminal 14 outputs the luminance of the high frequency range. The signal Y is taken out as Y=0.33YH. Since this luminance signal Y is obtained from the luminance signal YH which is not influenced by pixels of each color, the resolution of the image can be improved.

In addition, for the low frequency component, a luminance signal Y is output from the output terminal 14.
can be extracted as Y=0.3OR+0.59G+0.11B.

Here, the brightness signal Y for the high range is 0.33 compared to the low range.
However, by adjusting the gain in the high-frequency emphasizing circuit in the subsequent stage, no problem will arise.

In this way, in the circuit configuration of this embodiment, (YL-Y
There is no need for a differential circuit for obtaining the signal H) or an LPF for passing the differential signal (YL-Yl), and there is no need to consider the delay time with the luminance signal YL in the luminance signal circuit 5A.

Further, the coefficients α, β, and γ of the coefficient circuit 8.11.13 can be set by simply changing the resistance ratio, and the circuit can be simplified.

In the above embodiment, the color signals (R-YL) and (B-YL) obtained from the output terminals 15 and 16 are supplied to the next stage modulator.

Next, another embodiment in which the present invention is applied to a three-plate color imaging system in which three primary color signals are extracted using three imaging probes will be described with reference to FIGS. 2 and 3.

In the three-plate type of this embodiment, the resolution of the image sensor can be satisfied for each color, and as shown in FIG. 2(A),
As shown in (B) and (C), the red image sensor 17 is driven by the drive signal SHR, the green image sensor 18 is driven by the drive signal SHG, and the blue image sensor 19 is driven by the drive signal SHB. The resolution can be further increased by staggering the positions of the two.

In FIG. 3, primary color signals R, G, and B obtained from image pickup devices 17, 18, and 19 are supplied to a matrix circuit 6, and primary color signals R and G are supplied to a luminance signal circuit 20. In the matrix circuit 6, color difference signals (R-YL) and (B-Y[) are generated, similar to the circuit shown in FIG. The signal is supplied to the adder 9 via the adder 9.

In the luminance signal circuit 20, the luminance signal YH is extracted as YH-R+G by using the red and green primary color signals R and G, which have high light utilization efficiency, and are shifted in phase by 180 degrees. This luminance signal Y1 is supplied to the adder 9 via a delay circuit 23 and a coefficient circuit 24.

Each coefficient α, β, γ of coefficient circuit 24.21.22
To determine, (R + G + 8) in equation (2) is (R + G)
By replacing the red primary color signal R with
) For the green primary color signal G, 0, 59 = α-〇, 59β-〇, 59γ... (7) For the blue primary color signal B, o, i1 = -o, iiβ 10 γ - 0, 11 γ ...
(8), so these equations (6), (7), and (8)
From the formula, the coefficients α, β, and γ are determined as α=0.5 β−−0,25 γ−0,09.

By setting the coefficients of the coefficient circuits 24, 21, and 22 in this way, the high-frequency luminance signal Y can be extracted from the output terminal 25 as Y-αYH=0.5Y1, as shown in FIG. The S/N ratio improves as the value of α becomes larger compared to the circuit configuration.

As described above, according to this embodiment, the brightness signal YH is used for the high frequency portion, and the brightness signal Y is used for the low frequency portion.

In extracting the difference signal (YL-YH), the difference signal (YL-YH) becomes unnecessary.

Therefore, a differential circuit is not required, and a low-pass filter for passing the differential signal is also not required. Also, the difference signal (
Since YL-YH) is not used, there is no need to consider the delay between the signals YH and YL, and there is no need to provide a delay circuit in the luminance signal circuit that produces the luminance signal YH.

In this way, the circuit scale can be greatly simplified and a delay circuit is not required in the luminance signal circuit, so that the frequency characteristics and S/N ratio of the signal can be improved.

Furthermore, since no shift component occurs between the luminance signals YH and Y1, the quality of the image can be improved.

Note that a low-pass filter for color difference signals can be used, and the conventional low-pass filter for difference signals whose characteristics match those of color difference signals is not required.
Luminance signal Y that completely matches the band of the color difference signal from the adder
1 can be taken out and there are no restrictions on circuit characteristics.

[Effects of the Invention] As described above, according to the present invention, the frequency characteristics and S
Accordingly, it is possible to provide an image signal processing circuit that can improve the /N ratio, achieve high image quality, and is easy to configure.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of a video signal processing circuit according to the present invention, and FIG. 2 is a layout diagram of an image sensor, showing another embodiment in which the present invention is applied to a three-panel color imaging system. , FIG. 3 is a circuit diagram showing an embodiment of the same video signal processing circuit, FIG. 4 is a diagram showing an image sensor and sampling pulses, FIG. 5 is a diagram showing frequency bands of primary color signals and luminance signals, and FIG. The figure is a circuit diagram showing an example of a conventional video signal processing circuit. 1.17.18.19...Image sensor 2.3.4...Sampling circuit 5A, 20...Brightness signal circuit 6...Matrix circuit 7.23...Delay circuit 8.11.13 .21.22.24... Coefficient circuit 9.
... Addition circuit 10.12 ... Low-pass filter 14.15.16.25 ... Output terminal agent Patent attorney Nori Chika Ken Yudo Uji Hiroshi Figure (C) figure

Claims (1)

[Claims] a luminance signal generation circuit that generates a luminance signal Y_H by adding each primary color signal obtained by imaging at an equal ratio;
A first coefficient circuit that multiplies the luminance signal Y_H output from this luminance signal generation circuit by an arbitrary gain α and the composition ratio of the red, green, and blue primary color signals R, G, and B are R:G:
Luminance signal Y_ where B=0.30:0.59:0.11
A color difference signal generation circuit that generates color difference signals (R-Y_L) and (B-Y_L) using The color difference signal (B
-Y_L) by an arbitrary gain γ via a low-pass filter, and an adder that adds the respective output signals of the first, second, and third coefficient circuits. A video signal processing circuit characterized in that the output of the adder is extracted as a luminance signal Y.