JPH0456494A - Signal processing circuit for solid color image pickup element - Google Patents

Abstract

PURPOSE:To make a smear inconspicuous by eliminating a smear color without accompanying inferiority of the S/N of a luminance signal by providing a smear correcting circuit at the latter part of the low-pass filter of the route of a primary color signal which is primary-color separated. CONSTITUTION:The smear signal is eliminated by smear correcting circuits l, 1 and 1 only toward the primary color signals R, G, and B which are primary- color separated through sample-and-hold circuits 4r, 4g and 4b and low path filters 6, 6 and 6. Thus, since the smear correcting circuits 1, 1 and 1 do not influence the luminance signal at all, a smear correction can be executed without accompanying the inferiority of the S/N of the luminance signal. Therefore, it is possible to eliminate the smear color without inconvenience that vertical stripes generates as if it rains by the inferiority of the S/N of the luminance signal. And the smear becomes inconspicuous if only the color is eliminated.

Description

[Detailed description of the invention] The present invention will be described in the following order.

A. Industrial field of application B0 Overview of the invention C1 Prior art [Figs. 3 and 4] D0 Problems to be solved by the invention E1 Means for solving the problems F9 Effects G. Examples [First [Figure, Figure 2] a. One embodiment [Figure 1] b. Another embodiment [Figure 2] H1 Effects of the invention (A. Field of industrial application) The present invention relates to a processing circuit, and particularly to a signal processing circuit for a color solid-state image sensor that can prevent the occurrence of unsightly smear without deteriorating the S/N ratio of a luminance signal.

(B. Summary of the Invention) The present invention provides a signal processing circuit for a color solid-state image pickup device, in which the smear is made inconspicuous by erasing the color of the smear, without deteriorating the S/N ratio of the luminance signal. A smear correction circuit is provided after the low-pass filter in the path of the primary color signals separated into primary colors.

(C, Prior Art) [FIGS. 3 and 4] Smear occurs in a CCD type color solid-state image sensor when capturing an image of a high-brightness object. This is caused by receiving extra signal charge from the high-brightness light-receiving part, which did not originally have it, during the process in which the signal charge is transferred by the vertical register near the high-brightness light-receiving part. , appearing as vertical stripes.

The amount of smear generated does not vary much depending on the color filter arrangement because the cause of smear generation exists in the COD element itself, but the color of the smear varies greatly depending on the color filter arrangement and the primary color separation method. By the way, Ye(
Yellow) G (green) and Cy (cyan) arrays have the advantage of being able to accurately separate the primary colors using complementary color filters and have excellent color reproducibility, but the color of the smear is green (G).
This makes it look unnatural and very noticeable to people.

Even if there is a smear, it is not very noticeable if it is colorless, but it is noticeable if it is colored, especially if it is green.

Therefore, attempts have been made to remove the smear signal from the video signal by providing a smear correction circuit at the output of the CCD. Third
4 and 4 explain this smear signal removal technique, FIG. 3 is a circuit diagram of a smear correction circuit, and FIG. 4 is a circuit diagram of a smear correction circuit.
It is an output waveform diagram of D.

Reference numeral 1 denotes a smear correction circuit, which includes a line memory 2 that stores video signals for one horizontal scanning period, and a subtraction circuit 3 that subtracts the video signal read from the line memory 2 from the video signal output from the COD.

The smear correction circuit 1 reads the output signal of the CCD as a smear signal for one horizontal scanning period using the line memory 2 during the vertical blanking period (at this time, the switch is in the state shown by the solid line). This is because the signal from the optical black light receiving element is output during the vertical blanking period, so the video signal output during that period is only a smear signal, as shown in FIG. Therefore, the CCD output signal during the vertical blanking period is used as a smear signal.
The horizontal scanning period is stored in the line memory 2. In this case, in order to improve the S/N ratio, a smear signal for one horizontal scanning period may be obtained by synchronously adding a plurality of horizontal scanning periods during the vertical blanking period. Then, when the vertical blanking period ends and the video signal period begins, the line memory 2 is disconnected from the CCD output line and connected to the subtraction circuit 3 (at this time, the switch is in the state shown by the broken line).
The line memory 2 is stored in each horizontal scanning period by the subtraction circuit 3.
The smear signal read from the CCD is subtracted from the output signal of the CCD. Then, the output signal of the subtraction circuit 3 is transmitted as a smear-corrected video signal to the sample and hold circuits 4a to 4c for each color.

(D. Problem that the invention attempts to solve) By the way, the third problem
The smear correction method shown in the figure requires the S/N of the luminance signal.
There was a problem that deterioration occurred. That is, CC
This is because since the output of D is immediately smear corrected, noise enters the video signal when subtracting the smear signal from the video signal, which leads to deterioration of the S/N of the luminance signal.

This deterioration of S/N appears as a phenomenon in which the vertical stripes that appear in the video change subtly from field to field, making the video look as if it was raining, and as a result, the quality of the image becomes extremely poor. decreases.

The present invention has been made to solve these problems, and aims to make smears less noticeable by erasing the color of smears without deteriorating the S/N ratio of luminance signals. .

(E. Means for Solving the Problem) In order to solve the above problem, the signal processing circuit of the color solid-state image sensor according to claim (1) connects the smear correction circuit to a low pass path of the primary color signal separated into the primary colors. The signal processing circuit of a color solid-state image sensor according to claim 2, characterized in that the signal processing circuit is provided after the filter, is a color solid-state image sensor of a color separation type that has a primary color signal in which a smear signal is canceled in the process of primary color separation. The signal processing circuit is characterized in that the smear correction circuit is provided only in the primary color signal path where the smear signal is not canceled.

(F. Effect) According to the signal processing circuit of the color solid-state image sensor according to claim (1), since the smear signal is removed by the smear correction circuit from the primary color signals separated into primary colors, the smear signal does not affect the luminance signal at all. In other words, can the color of the smear be changed without deterioration of the S/N of the luminance signal? It can take portraits and make smears less noticeable. In this case, a colorless smear occurs, but there is no problem because the smear is hardly noticeable without color and causes almost no deterioration in image quality.

According to the signal processing circuit of the color solid-state image sensor according to claim (2), since the smear correction circuit is not provided for the primary color signal whose smear signal is canceled during the primary color separation process, the number of smear correction circuits is reduced. be able to.

(G. Embodiment) [FIGS. 1 and 2] Hereinafter, the signal processing circuit of the color solid-state image sensor of the present invention will be described in detail according to the illustrated embodiment.

(A, One Embodiment) [FIG. 1] FIG. 1 is a circuit block diagram showing one embodiment of a signal processing circuit of a color solid-state image sensor according to the present invention.

In this embodiment, the present invention is applied to a signal processing circuit of a color solid-state image sensor with color filters arranged in an RGB arrangement. 4
r, 4g, and 4b are sample-hold circuits that sample each red, green, and blue signal; 5 is a luminance matrix that extracts the luminance signal Y from the output of each sample-and-hold circuit 4r, 4g, and 4b; 6.6.6 is each sample hold circuit 4r
, 4g, and a low-pass filter provided on the output side of 4b,
1.1.1 is a smear correction circuit provided on the output side (later stage) of the low-pass filter 6.6.6, and it has the same circuit configuration as the smear correction circuit shown in Figure 3. (
A specific circuit is shown for the smear correction circuit 1 for the red primary color signal, but since the smear correction circuit 1.1 for the green and blue primary color signals has the same circuit configuration, the specific circuit is not shown and is shown as a black box. . ). However, the storage capacity of the line memory 2 is smaller than that of the smear correction circuit shown in FIG. It's over.

The output signal of each smear correction circuit 11.1.1 passes through an amplifier 7 and a gamma correction circuit 8, respectively, to a color difference matrix 9.
The color difference matrix 9 generates two color difference signals RY and BY.

The signal processing circuit of this color solid-state image sensor includes sample-hold circuits 4r, 4g, 4b and low-pass filters 6.6.
．． Since the smear correction circuit 1.1.1 removes smear signals only for the primary color signals R, G, and B that have been separated into primary colors through step 6, the smear correction circuit 1.1.1 does not affect the luminance signal at all. . Therefore, smear correction is performed using S/
This can be done without deterioration of N.

Therefore, the color of the smear can be erased without the inconvenience of vertical stripes appearing as if it were raining due to deterioration of the S/N of the luminance signal. And, as long as the color is removed, the smear becomes almost invisible, so there is no problem.

Furthermore, as shown in Fig. 3, smear correction is not performed on the output signal of the CCD, but on the primary color signal that has passed through the low-pass filter 6, so the storage capacity of the line memory is small. It's over.

(b. Other Embodiments) [FIG. 2] FIG. 2 is a circuit block diagram showing another embodiment of the signal processing circuit of the color solid-state image sensing device of the present invention.

In this example, the color filter array is Ye (yellow) and G.
(green), the present invention is applied to a signal processing circuit of a color solid-state image sensor with a Cy (cyan) arrangement, and green (G)
Smear correction is applied only to the primary color signals. This is because the smear signals for the red (R) and blue (B) primary color signals are canceled (corrected) at the stage of primary color separation, so there is no need to provide a smear correction circuit to perform smear correction. be. The reason for this is explained below.

A color solid-state image sensor with a Ye, G, Cy arrangement obtains a primary color signal R by subtracting G from Ye (10a is a subtraction circuit that performs the subtraction), and by subtracting G from Cy (10b is a subtraction circuit that performs the subtraction). Subtraction circuit that performs subtraction) Obtains B. Further, G is used as it is as the primary color signal G.

By the way, when smear occurs, each pixel signal Ye, Cy
, G are superimposed with the same level of smear amount Δ. This smear amount Δ is not proportional to the output of the CCD. Here, the signal obtained by superimposing the smear amount △ on the pixel signals Ye, Cy, and G is Ye'
, Cy' , G'', then Ye' ==Ye+△, cy =cy+△, G
=G+△.

If we consider the primary color separation equation here, the following equation holds true.

R=Ye"-G'=CYe+△)-(G+
△)=Ye-G B=Cy'-G'=CCy+△)-(G+
△)=Cy-G G=G+△ Therefore, the smear signal is canceled for the red primary color signal R1 and the blue primary color signal B, and the smear signal remains superimposed only for the green primary color signal G. It can be said that. And actually before (C, prior art section)
As mentioned above, the smear appears green in the image.

Therefore, the smear correction circuit 1 is provided on the output side of the low-pass filter in the path of the green primary color signal G, and the other primary color signals R, B are
There is no need to provide a smear correction circuit in the path.

Incidentally, if a smear correction circuit is provided even though it is not necessary, it can be said that it will only worsen the S/N etc.

In this manner, in the case of a primary color separation method in which there are primary color signals whose smear signals are canceled due to primary color separation, it is not necessary to provide a smear correction circuit for all primary color signals whose smear is canceled.

(H. Effect of the invention) As described above, the signal processing circuit of the color solid-state image sensor according to claim (1) stores the video signal for one horizontal scanning period during the vertical blanking period as a smear signal. A smear correction circuit consisting of a line memory and a subtraction circuit that subtracts the smear signal stored in the line memory from the video signal every horizontal scanning period during the video period is installed after the low bass filter in the primary color signal path where the primary colors are separated. It is characterized by the fact that it is provided in

Therefore, according to the signal processing circuit of the color solid-state image sensor of the present invention, since the smear correction circuit removes the smear signal from the primary color signals separated into the primary colors, the smear signal does not affect the luminance signal at all (i.e., the luminance signal The color of the smear can be erased without deteriorating the S/N ratio, and the smear can be made less noticeable.

Furthermore, since smear correction is performed on the primary color signal that has passed through the low-pass filter, the storage capacity of the line memory can be small.

The signal processing circuit of the color solid-state image sensor according to claim (2) includes:
In the signal processing circuit of a color separation type color solid-state image sensor with a primary color signal in which the smear signal is canceled during the primary color separation process, a line memory stores the video signal as a smear signal for the horizontal scanning period during the vertical blanking period. In addition, a smear correction circuit consisting of a subtraction circuit that subtracts the smear signal stored in the line memory from the video signal every horizontal scanning period during the video period is provided only on the path of the primary color signal where the smear signal is not canceled. This is a characteristic feature.

Therefore, according to the signal processing circuit of a color solid-state image sensor according to claim (2), since a smear correction circuit is not provided for the primary color signal whose smear signal is canceled in the process of primary color separation, the number of smear correction circuits is reduced. It can be reduced.

[Brief Description of the Drawings] Fig. 1 is a circuit block diagram showing one embodiment of the signal processing circuit of the color solid-state image sensor of the present invention, and Fig. 2 is a circuit block diagram showing another embodiment of the signal processing circuit of the color solid-state image sensor of the present invention. FIG. 3 is a circuit block diagram showing an embodiment, FIG. 3 is a circuit block diagram showing a conventional example, and FIG. 4 is a waveform diagram of a CCD output signal. Explanation of symbols 1...Smear correction circuit, 2...Line memory, 3...Subtraction circuit, 6 (LPF)...Low pass filter. Figure 1 Circuit diagram of conventional 471j Figure 3 CCD output waveform diagram Figure 4 Figure 2

Claims (2)

[Claims] (1) A line memory that stores the video signal for one horizontal scanning period during the vertical blanking period as a smear signal, and a smear signal that is stored in the line memory and read out for each horizontal scanning period during the video period. A signal processing circuit for a color solid-state image pickup device, characterized in that a subtraction circuit for subtracting from a video signal, and a smear correction circuit comprising a smear correction circuit are provided after a low-pass filter in a primary color signal path where primary colors are separated. (2) In the signal processing circuit of a color separation type color solid-state image sensor with a primary color signal in which the smear signal is canceled during the primary color separation process, the video signal for the horizontal scanning period during the vertical blanking period is stored as a smear signal. and a subtraction circuit that subtracts the smear signal stored in the line memory and read out in each horizontal scanning period from the video signal during the video period. A signal processing circuit for a color solid-state image sensor characterized by being provided only after the low-pass filter in the signal path.