JPH04315393A - Vertical false signal suppression system in color camera - Google Patents

Abstract

PURPOSE:To provide the vertical false signal suppression system to reduce a vertical false signal generated in a vertical edge part of a pattern in the color camera employing an image pickup element provided with the color difference line sequential system color filter. CONSTITUTION:A simultaneous processing circuit used for the vertical false signal suppression system is provided with a correlation detection circuit 32 receiving an output Y0 of a 1H delay circuit for a broad band luminance signal YH, an output Y-1 after the output YH by 1H and an output Y+1 before the output YH by 1H and generating two coefficients K-1=Y0/Y-1, K+1=Y0/Y+1, multipliers 33, 34 multiplying respectively the two coefficients with a signal C-1 before 1H and a signal C+1 after 1H, and an adder 35 averaging outputs of the multipliers 33, 34, an attenuator circuit 36 and a changeover switch 37 outputting the outputs a, b of the multipliers 33, 34 and an output (c) of the attenuator circuit 36 as an interpolation signal C0' selectively in response to the intensity of the luminance signal.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention is a vertical false signal suppression method for reducing vertical false signals generated at the vertical edges of the screen in a color camera using a solid-state image sensor equipped with a color filter of the color difference line sequential method. Regarding.

0002

2. Description of the Related Art Conventionally, a solid-state image pickup device equipped with a color filter of a color difference line sequential system has a means for separating a luminance signal and a line sequential color difference signal from an output signal, and two signals obtained by synchronizing the line sequential color difference signals are provided. A color camera is known that generates R, G, and B signals from a color difference signal and a luminance signal, and forms a chroma signal using the R, G, and B signals. Next, an example of the configuration of a color camera of this type will be explained based on FIG. 4. In the figure, 1 is an imager, and the output of the imager 1 is input to a wideband low-pass filter (LPFH) 2 and a color separation circuit 8.
A broadband luminance signal YH is generated by the PFH ) 2, and a line sequential color difference signal CR /CB is generated by the color separation circuit 8 . The luminance signal YH is input to a 1H delay circuit 3, and the output of the 1H delay circuit 3 is further input to a 1H delay circuit 4. The input and output signals of the 1H delay circuit 3 and the output of the 1H delay circuit 4 are input to a DTL signal generation circuit 5, and horizontal and vertical DTL signals are generated. The output of the 1H delay circuit 3 and the DTL signal are added in an adder circuit 6, and gamma correction is applied in a gamma correction circuit 7. Also, 1H delay circuit 3
The output of the R. G. The signal is input to the B matrix circuit 11.

On the other hand, the line sequential color difference signal CR /CB outputted from the color separation circuit 8 is separated into synchronized color difference signals CR and CB by the synchronization circuit 10 . This synchronization circuit 10 will be explained later using FIG. R. G. In the B matrix circuit 11, R
, G, B signals are generated. The R and B signals output from the matrix circuit 11 are transmitted to white balance circuits 12 and 13.
After gain control is performed so that the signal level is the same as that of the G signal, gamma correction circuits 14 and 16 apply gamma correction to each signal. Also, the G signal is also gamma correction circuit 1
5 adds gamma correction. A modulated color signal C is generated by the encoder 17 based on each of the R, G, and B signals to which gamma correction has been added, and this modulated color signal C, the broadband luminance signal YH, and the synchronization signal SYNC are added together by the adder circuit 18. and a VBS signal is generated. Note that the broadband luminance signal YH has two 1H delay circuits 3.
, 4, so this is expressed as Y0 based on the output of the 1H delay circuit 3, and the signal 1H before is expressed as Y-1, and the signal after 1H is expressed as Y+1. are doing.

Next, the synchronization circuit shown in FIG. 5 will be explained. The line sequential color difference signal CR/CB outputted from the color separation circuit 8 in FIG.
It passes through the H delay circuit 20. These two 1H delay circuits 1
Since there are temporally different signals due to 9 and 20, 1
The output of the H delay circuit 19 is referred to as C0, the signal 1H before it is C-1, and the signal 1H later is C+.
1. Next, the adder circuit 21 and the attenuator circuit 22 calculate the average value of C-1 and C+1, and use this as the interpolation signal C0'. Switches 23 and 24 are 1/
It is a switch that switches the output every H using a square wave pulse fH/2 whose level changes in two cycles as a control signal,
These switches 23 and 24 alternately select and output the line-sequential color difference signal C0 directly obtained from the imager and the interpolation signal C0'. As a result, the color difference signal CR
, CB are output.

[0005]

[Problems to be Solved by the Invention] By the way, a color filter for a color camera using the color difference line sequential method is described in, for example, the TV Society Journal, 1983, VOL. 37, No.
10, entitled "Single-chip colorization method for field accumulation mode CCD", as shown in Figure 4, generally the imager output is passed through a low-pass filter, and the luminance signal Y is passed through a color separation circuit. It is known to obtain line-sequential color difference signals CR/CB. At this time, in the color filter shown in the above paper, C
Cy, Ye, Mg, and G filters that satisfy the conditions y=G+B, Ye=R+G, and Mg=R+B are used, and the luminance signal Y and color difference signals CR and CB shown in the following equation (1) can be obtained. There is. Y=2R+3G+2B
CR=2R-G CB=2B-G

・・・・・・(1)

Considering the improvement of color reproducibility, as shown in FIG.
Once R, G, B signals are generated from
Ideally, after gamma correction is applied to each signal, color difference signals (R-Y) and (B-Y) are created again, and these are used as the modulated color signal C. Calculating R, G, and B from equation (1), R=0.1(Y+4CR −CB )
G=0.2(Y-CR-CB)
B=0.1(Y-CR+4CB)
・・・・・・
...(2) is derived. Furthermore, in order to maintain white balance, the R and B signals are set as shown in FIG. 4 so that the R and B signal levels match the G signal level during achromatic color imaging.
Constant GR in white balance circuits 12 and 13, respectively
, GB is multiplied, R=0.1(Y+4CR -CB)
×GR G=0.2(Y-CR-C
B) B=0.1(Y-CR+4C
B)×GB...
...(3) is generated.

Generally, the characteristics of color filters are selected so that the levels of the color difference signals CR and CB are as low as possible during achromatic imaging, but they do not become zero. Further, in the case of achromatic color, since the level ratios of Cy, Ye, Mg, and G are constant, the level ratios of CR, CB, and Y are also constant, and there is a relationship expressed by the following equation (4). CR=KR Y CB=KB Y

・・・・・・(4) (However, KR and KB are constants) Under the condition of the above equation (4), R=G= in the equation (3)
GR and GB are adjusted so that the image becomes B, that is, the white balance is maintained.

By the way, the above equation (2) does not hold unless the luminance signal Y and color difference signals CR and CB exist simultaneously. However, in this type of color camera, the color difference signal C
Since R and CB are output from the imager line-sequentially, it is necessary to synchronize the color difference signals CR and CB. Therefore, a synchronization circuit 10 is used as shown in FIG. Conventionally, as a synchronization means, a method has been used in which interpolation is performed using the average value of signals around 1H, as shown in FIG.

FIG. 7 shows a vertical waveform when a subject as shown in FIG. 6 is photographed using the color camera configured as described above. In addition, in FIG. 7, for simplification,
The horizontal blanking period is omitted. here,
The white level of the luminance signal Y is 1.0, and the gray level is 0.5.0.
．． 25. Normalize the black level to 0. Also, KR = 0.
5. It is assumed that the relationship KB = 0.25 holds true.

In FIG. 7, (A) shows the narrowband luminance signal YL after 1H delay in FIG. 4, (B) shows the line sequential color difference signal CR /CB after 1H delay in FIG. The output color difference signal CR is shown in (C), and the output color difference signal CB is shown in (D).

In FIGS. 7C and 7D, the thick line shows a signal interpolated with the average value of signals around 1H, and the broken line shows an ideal waveform. The ideal waveform is KR =
This waveform satisfies CR /Y = 0.5, KB = CB /Y = 0.25, and where there is a difference between the broken line and the thick line, it violates the conditions for achieving white balance. In other words, in the conventional synchronization method in which interpolation is performed using the average value of signals around 1H, if there is poor vertical correlation in the vertical direction, for example, at edges with large black and white contrast, the error between the interpolated signal waveform and the ideal waveform is large. However, there was a problem in that false color signals were generated and the image quality deteriorated.

The present invention has been made in order to solve the above-mentioned problems in the conventional color difference line sequential color camera. The purpose of this paper is to provide a vertical false signal suppression method for color cameras.

[0013]

[Means and operations for solving the problems] In order to solve the above-mentioned problems, the present invention separates a luminance signal and a line-sequential color difference signal from an output signal of a solid-state image sensor equipped with a color filter of a color-difference line-sequential method. R, G, B from two color difference signals and a luminance signal obtained by synchronizing line-sequential color difference signals.
In a color camera that generates a signal and forms a chroma signal using the R, G, and B signals, when synchronizing line-sequential color difference signals, the ratio of the luminance signal of the line to be interpolated to the luminance signal of the previous and succeeding lines is determined. , the signals obtained by multiplying the color difference signals of the front and rear lines, respectively, are selectively used as interpolation signals according to the intensity of the luminance signal.

By using such an interpolation signal,
The line-sequential color difference signal is interpolated with a signal selected according to the strength of the luminance signal from among the signals obtained by multiplying the color difference signals of the previous and succeeding lines by the ratio of the luminance signal of the line to be interpolated and the previous and subsequent lines. Therefore, when line-sequential color difference signals are synchronized, there is no error from the ideal waveform even at edge portions with large contrast between black and white, and the generation of false signals is effectively suppressed.

[0015]

[Example] Next, an example will be explained. FIG. 1 is a diagram showing the overall configuration of a color camera using a color difference line sequential method for explaining an embodiment of the vertical false signal suppression method according to the present invention.
The same reference numerals are given to the same or equivalent members as those of the conventional one shown in FIG. 4, and the explanation thereof will be omitted. In the circuit configuration of the color camera used in the present invention, the only difference from the conventional one is the line-sequential color difference signal CR /CB synchronization circuit 31, which will be explained based on FIG. 2. As shown in FIG. 2, the synchronization circuit 31 used in the present invention converts the output Y0 of the 1H delay circuit 3 of the wideband luminance signal YH, the output Y-1 1H before that, and the output Y+1 1H after that, The luminance signal Y0 of each line to be input and interpolated
2 from the ratio of the brightness signals Y-1 and Y+1 of the front and rear lines.
coefficients K-1=Y0/Y-1, K+1=Y0/Y
+1, respectively, and a coefficient generation circuit 32 that generates the two coefficients K-1 and K+1 as a line-sequential color difference signal CR/CB.
With the output C0 of the 1H delay circuit 19 as a reference, the signal C-1 1H earlier and the 1H delay circuit 20
Multipliers 33 and 3 that respectively multiply the signal C+1 after H
4, an adder 35 that adds the outputs a and b of each multiplier 33 and 34, an attenuator circuit 36 that halves the output of the adder 35, and outputs a and b of the multipliers 33 and 34. and the output c of the attenuator circuit 36, and inputs the brightness signals Y-1 and Y+1 of the lines before and after the line to be interpolated. and a switch control signal generation circuit 38 that sends out a switching control signal for the changeover switch 37.

Here, C-1, Y-1 correspond to the line-sequential color difference signal 1H before the line to be interpolated and the luminance signal 1H before, and C0, Y0 correspond to the line-sequential color difference signal and the luminance signal 1H before the line to be interpolated. Corresponding to the signals, C+1 and Y+1 correspond to a line-sequential color difference signal 1H after the line to be interpolated and a luminance signal 1H after the line to be interpolated.

Next, the operation of the synchronization circuit 31 having such a configuration will be explained. First, the coefficient generation circuit 32 calculates the ratio between the luminance signal Y0 of the line to be interpolated and the luminance signals Y-1 and Y+1 of the previous and succeeding lines, and calculates the two coefficients K-1=Y0/Y-1 and K+1=Y0. /Y+
Generates 1. Next, in multipliers 33 and 34, the two coefficients K-1 and K+ generated from the coefficient generation circuit 32 are
1 by the signal C-1 before 1H and the signal C+1 after 1H, respectively. In addition, the outputs a=K-1×C-1 and b=K+1×C+1 of these multipliers 33 and 34 are added by an adder 35 and halved by an attenuator circuit 36, so that the outputs of the multipliers 33 and 34 are The average value of the output of c = (K
−1×C−1+K+1×C+1)×1/2 is output from the attenuator circuit 36. Output a of the multipliers 33 and 34
, b and the output c of the attenuator circuit 36.
input to each switching terminal of 7.

On the other hand, the switch control signal generating circuit 38 inputs the luminance signals Y-1 and Y+1 of the lines around 1H, and controls the changeover switch 37 in the following manner based on the control signal generated based thereon. That is, Y-1>Y
If +1, output a; if Y-1<Y+1, output b
, if Y-1=Y+1, output c, selector switch 2
Control is performed to selectively output to 3 and 24.

In this way, the luminance signal Y of the line around 1H
Since the interpolation signal is formed by multiplying the signal of the larger line of -1 and Y+1 by the smaller coefficient, the effect of reducing noise can be obtained. However, if the luminance signals Y-1 and Y+1 of the lines before and after 1H are close to zero, the coefficient K-1
, K+1, so an interpolation signal is formed by setting K-1=K+1=1.

By using the synchronization circuit that performs synchronization processing of line-sequential color difference signals as described above, the interpolated color difference signals CR and CB when photographing the subject shown in FIG. , (D), it can be seen that even edge portions with large contrast between black and white have ideal waveforms with almost no errors, and false signals are suppressed. In addition, in FIG. 6, the values of coefficients K-1 and K+1 and the changeover switch 3 are shown.
7 switching modes are also shown.

[0021]

[Effect of the invention] As explained above based on the embodiments,
According to the present invention, the line-sequential color difference signal is obtained by multiplying the color difference signal of the previous and succeeding lines by the respective ratios of the luminance signal of the line to be interpolated and the luminance signals of the preceding and succeeding lines. Interpolation is performed using an interpolation signal selected according to the signal, and as a result, there is no error from the ideal waveform even at edge portions with large contrast between black and white, and the generation of false signals is effectively suppressed.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a circuit configuration of a color camera for explaining an embodiment of a vertical false signal suppression method in a color camera according to the present invention.

FIG. 2 is a diagram showing a detailed circuit configuration of the synchronization circuit in FIG. 1;

FIG. 3 is a signal waveform diagram for explaining the operation of the synchronization circuit shown in FIG. 2;

FIG. 4 is a diagram showing a circuit configuration of a conventional color difference line sequential color camera.

FIG. 5 is a diagram showing a detailed circuit configuration of the synchronization circuit in FIG. 4;

FIG. 6 is a diagram showing an example of a pattern of a subject to be photographed.

7 is a signal waveform diagram for explaining the operation of the synchronization circuit shown in FIG. 4. FIG.

[Explanation of symbols]

1 Imager 2 Wideband low-pass filter 5 DTL signal generation circuit 8 Color separation circuit 9 Narrow band low pass filter 11 R. G. B matrix circuit 12,13 White balance circuit 17 Encoder 31 Simultaneous circuit 32 Coefficient generation circuit 33 Multiplier 34 Multiplier 35 Adder 36 Attenuator circuit 37 Selector switch 38 Switch control signal generation circuit

Claims (1)

[Claims] 1. Two color difference signals obtained by synchronizing the line sequential color difference signals, comprising means for separating a luminance signal and a line sequential color difference signal from an output signal of a solid-state image sensor equipped with a color filter of a color difference line sequential method. In a color camera that generates R, G, and B signals from a luminance signal and a chroma signal from the R, G, and B signals, when line-sequential color difference signals are synchronized, the luminance signal of the line to be interpolated and the previous and subsequent lines are A vertical false signal suppression method characterized in that signals obtained by multiplying the color difference signals of the front and rear lines by respective ratios with the luminance signals are selectively used as interpolation signals according to the strength of the luminance signals.