JP2823264B2 - Video signal processing circuit - Google Patents

Description

The present invention relates to a video signal processing circuit of a single-panel type color imaging device.

(B) Conventional technology A solid-state image pickup device mounted on a single-chip color image pickup device such as a video camera is provided with a stripe-like or mosaic-like color separation filter, and light-receiving pixels of the solid-state image pickup device correspond to each color component. Attached. The surrounding area of the imaging unit is shielded from light for several pixels, and an optical black area (OPB area) is provided. A video signal output from such a solid-state imaging device for each horizontal line has color components corresponding to a color separation filter repeatedly in a predetermined order, and has an OPB component obtained from an OPB area at an end of each horizontal line. And this
After the OPB component is clamped and the reference level is fixed, sampling is performed at different timings and separated for each color component.

FIG. 3 is a block diagram showing a processing circuit for a video signal as described above, and FIG. 4 is a timing chart thereof. Here, yellow (Ye), green (G), cyan (Cy)
2 shows a video signal Y obtained from a CCD solid-state imaging device provided with the stripe filter of FIG.

The video signal Y repeats each component of Ye, G, and Cy in a period I during which a signal is output from a region where a color separation filter is mounted, and a period II during which a signal from an OPB region is output.
Shows the OPB component. This OPB component indicates a dark current component of the solid-state imaging device, and this level is a reference level of a video signal,
That is, it is at the black level. Then, a period III between each horizontal line, which is a blanking period of horizontal scanning of the solid-state image sensor,
Is a period during which the horizontal line is transferred in the vertical direction. Since the horizontal transfer drive is suspended, no signal is output from the solid-state imaging device itself, and noise or the like superimposed at the output section of the solid-state imaging device is Appears.

This video signal Y is input to the clamp circuit (1),
OPB component is clamped in accordance with the clamp pulse CP ₁ synchronized with the period II to obtain the OPB component. The video signal Y with the OPB component clamped is next input to a blanking circuit (2), and is blanked in accordance with a blanking signal BK over a period II to III. That is, the video signal Y after the OPB component is clamped is removed except for a period I in which each color component is repeatedly shown, and is equal to the clamp level of the clamp circuit (1) in the next pedestal clip circuit (3). A voltage value is given in periods II and III, and a reference level is set. Therefore, a video signal Y 'having a fixed black level can be obtained.

The video signal Y 'having the fixed black level is input to three sample-and-hold circuits (5a), (5b), and (5c) after the gain is adjusted by an automatic gain control (AGC) circuit (4). The sample-and-hold circuits (5a), (5b), and (5c) sequentially operate at different timings according to a sampling clock SC synchronized with a horizontal transfer clock of the solid-state imaging device.
Each component of Ye, Cy and G is sampled and held. That is, Y
By sampling and holding a video signal Y 'that repeats each component of e, Cy, and G at a timing synchronized with the repetition,
Each color component signal is separated into Ye, Cy and G. Then, by subtracting the color component signal G from the color component signals Ye and Cy, respectively,
Color component signals R and B indicating red (R) and blue (B) are obtained.

These color component signals R, B and G, each clamp circuit according to a clamp pulse CP ₂ is synchronized with the period III (6a) (6b)
In (6c), each is clamped on the basis of the black level given to the video signal Y 'in the preceding stage, and the next blanking circuit (7a)
(7b) After the blanking is applied in accordance with the blanking signal BK in the same manner as the video signal Y in (7c), the level equal to the clamp level of the clamp circuit (1), that is, the black level of the video signal Y becomes pedestal clip ( 8a) (8b)
Given in (8c). Therefore, when the reference level is the video signal Y
Are obtained, and the color component signals R, B, and G are fixed to the black level given to the first stage, and these color component signals R, B, and G are supplied to a signal processing circuit (not shown) at the next stage.

(C) Problems to be Solved by the Invention In the video signal processing circuit as described above, the video signal Y set by the first-stage clamp circuit (1), blanking circuit (2), and pedestal clip circuit (3) ', The color component signals separated into the respective color components are processed with reference to the black level, so that when the black level fluctuates, the clamp circuits (6a) (6b) (6c) and the pedestal clip circuits (8a) (8b) The operation of (8c) becomes unstable, and the color component signal
The balance between R, B and G is lost. That is, when the black level of the video signal Y ′ changes, the color component signals R and B are canceled by subtracting the color component signal G from the color component signals Ye and Cy. Since the variation of the black level is superimposed as it is, the balance of the color component signals R, B, and G is lost, and the color reproducibility is reduced.

In addition, a clamp circuit (1) and a blanking circuit (2)
Also, the black level of the video signal Y 'may fluctuate depending on the temperature characteristics of the pedestal clip circuit (3) itself, and there is a possibility that the balance of each color component cannot be maintained with respect to the temperature change.

As means for suppressing such a change in the balance of each color component, clamping of the OPB component performed at the stage of the video signal Y is performed at the stage of the color component signals Ye, Cy, and G after separation for each color component. Considering the calculation for obtaining the next-stage color component signals R and B, the adjustment of the operating characteristics of the clamp circuit corresponding to each component becomes extremely fine, and each setting becomes complicated. . Further, in the color component signals R and B obtained by subtracting the color component signal G from the color component signals Ye and Cy, since the OPB component is canceled, the OPB component is clamped at the stage of the color component signals R and B. It is difficult to do.

Accordingly, it is an object of the present invention to provide a video signal processing circuit that can easily adjust the balance of each color component and can obtain a stable operation.

(D) Means for Solving the Problems The present invention has been made to solve the above problems, and first to third color separation filters are provided on the pixels of the imaging unit in correspondence with the respective pixels. An image for separating a video signal continuously output for each horizontal line from a solid-state imaging device in which pixels around an imaging unit are shielded from light for each of first to third color components and setting a reference value for each video signal In the signal processing circuit, the video signal is clamped during a first period in which a signal from the light-shielded pixel is obtained, and a reference value corresponding to the clamp level follows the first period between horizontal lines. Second
A first reference value setting unit that replaces the video signal during the period, sample-holds the video signal sequentially at first to third timings, and separates the video signal into first to third color components;
A color separation means for subtracting the third color component from the first and second color components to obtain fourth and fifth color components, wherein the third color component signal is clamped during the first period, and A second reference value setting for clamping the fourth and fifth color component signals in the second period and replacing a reference value corresponding to each clamp level with the color component signal in the first and second periods. Means.

(E) Operation According to the present invention, the fourth and fifth color component signals are obtained by subtracting the third color component signal from the first and second color component signals, and thus are separated into respective color components. Even if the black level of the video signal fluctuates in the stage before the change, the fluctuation is canceled and the black level of the third color component signal is set again in the same manner as the black level of the video signal. The correction is performed, and the third to fifth color component signals are less likely to undergo a change in the black level of the video signal.

(F) Embodiment One embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a video signal processing circuit of the present invention, and FIG. 2 is an operation timing diagram thereof. In this figure, a clamp circuit, a blanking circuit,
The pedestal clip circuit and the sample-and-hold circuit have the same configuration as in FIG. 3, and the same parts are denoted by the same reference numerals.

The video signal Y given to the clamp circuit (1)
Although components are clamped in accordance with the clamp pulse CP ₁ to be synchronized to the period II obtained, following the blanking circuit (2)
Then, blanking is applied only to period III except for period II. That is, the blanking signal BK ₁
Is set to blank only on the OP
In the period II indicating the B component, the OPB component is left as it is. Therefore, the video signal Y 'input to the AGC circuit (4) shows an OPB component clamped to a predetermined level in the period II,
A period III indicates a reference level given by the pedestal clip circuit (3). This video signal Y 'is separated into color component signals Ye, Cy and G by the sample and hold circuits (5a), (5b) and (5c), and then the color component signal G is converted to the color component signals Ye and Cy.
And the color component signals R and B are subtracted. The color component signals R and B, OPB component and the video signal black level variation of occurring in Y 'is canceled, the clamp circuit (6a) (6 accordance clamp pulse CP ₂ which is synchronized with the period III
b) Clamped.

On the other hand, the color component signal G includes a variation of the black level caused OPB component video signal Y ', it is again clamped in the clamp circuit (6c) in accordance with the clamp pulse CP ₁ to be synchronized to the period II shown the OPB component The black level is set. Therefore, even if a change occurs in the black level of the video signal Y ', the OPB component is clamped again by the clamp circuit (6c), so that the change in the black level is corrected.

The color component signals R, B, and G clamped by the clamp circuits (6a), (6b), and (6c) are input to the blanking circuits (7a), (7b), and (7c), respectively, and the blanking signals BK After blanking is applied to the periods II and III according to _{2, the} reference value equal to the clamp level of the clamp circuit (1) is set in the pedestal clip circuits (8a), (8b), and (8c).
Given to II, III. Therefore, color component signals R, B, and G having a fixed black level can be obtained.

In the present embodiment, a case where a striped color separation filter made of Ye, G and Cy is mounted is illustrated, but the mosaic color is changed by changing the sampling timing of the sample and hold circuit. Applicable to separation filters. Further, the present invention can be similarly used in a color separation filter having a two-layer structure for obtaining G by partially overlapping Ye and Cy.

(G) Effects of the Invention According to the present invention, even when the reference value of the video signal fluctuates, the balance of the color component signals can be maintained.
The temperature characteristic of the circuit for setting the reference value of the video signal does not cause much problem, and the degree of freedom in designing each circuit increases.

Further, the adjustment of the circuit for setting the reference value of the color component signal can be simplified, the operation of each circuit can be stabilized, and the reduction in color reproducibility can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a video signal processing circuit of the present invention, FIG. 2 is a timing chart showing the operation of FIG. 1, FIG. 3 is a circuit diagram showing a conventional video signal processing circuit, and FIG. Third
FIG. 4 is a timing chart showing the operation of the figure. (1) (6a) (6b) (6c) ... Clamp circuit (2)
(7a) (7b) (7c) ... Blanking circuit, (3) (8
a) (8b) (8c)… pedestal clip circuit.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 9/64 H04N 9/07

Claims (1)

(57) [Claims] A first to a third color separation filter is provided on each pixel of an image pickup unit so as to correspond to each pixel, and pixels around the image pickup unit are continuously arranged for each horizontal line from a light-shielded solid-state image sensor. A video signal processing circuit for separating a video signal to be output for each of first to third color components and setting a reference value of each video signal, wherein a first period for obtaining a signal from the light-shielded pixel First reference value setting means for clamping the video signal, and replacing a reference value corresponding to the clamp level with the video signal in a second period following the first period between horizontal lines; The signal is sequentially sampled and held at the first to third timings to separate the signals into first to third color components.
Is subtracted from the first and second color components, respectively.
And a color separating means for obtaining a fifth color component, wherein the third color component signal is clamped in the first period and the fourth and fifth color component signals are clamped in the second period. Video signal processing circuit, comprising: a second reference value setting means for replacing a reference value according to a clamp level with the color component signal in the first and second periods.