JPS59219087A - Signal processing circuit - Google Patents

Abstract

PURPOSE:To eliminate a chrominance error by clipping a level being a prescribed level or over of an output signal of a solid-state image pickup element using a complementary color to make the incident luminous amount where an ou tput signal of each hue is saturated identical as a result. CONSTITUTION:Ye, Cy signals among W, Ye, Cy signals outputted from asolid- state image pickup element 4 are clipped by a signal amount at the saturated incident luminous amount of the W by signal processing circuits 8, 9 and the result is applied to subtractors 10, 11. As a result, the subtractors 10, 11 conduct operation of B=W-Ye and R=W-Cy without error and without chrominance error even at an amount being the saturated incident luminous amount of the W. That is, B, R signals with fidelity to the color of an object are outputted to lines 12 and 13. The saturated incident luminous amount of an output signal of each hue is made idential as a result to eliminate a chrominance error.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a signal processing circuit for a video camera, and in particular,
The present invention relates to a signal processing circuit that can ultimately make the same amount of incident light at which output signals of each hue of a solid-state image sensor using complementary colors are saturated.

[Background of the invention]

In a video camera, for example, the output signal corresponding to the amount of incident light of a solid-state image sensor using the colors of white (w), yellow (Ye), and cyan (Oy) has the characteristics shown in curves 1 to 3 in Fig. 1, respectively. are doing. As is clear from Fig. 1, the incident light point at which the output (g) is saturated (hereinafter referred to as the saturated incident light point) is different from one another.In other words, as the amount of incident light increases, the output signal becomes saturated. Yo W.

The order is Ye and Cy. This is because the transmittance of the filters for each hue is different.

On the other hand, for image sensors that use complementary colors, the primary colors are red.

(mentioned above) can be understood as the calculation of Le-Cy and B-W-Ye. Therefore, when the W saturation incident scene is exceeded, the signal of W decreases, but Ye and Cy increase.
This will result in a decrease by e fi. As a result, conventional video cameras using the solid-state image pickup device have the disadvantage that a color error of ΔR;

[Purpose of the invention]

An object of the present invention is to provide a signal processing circuit that can eliminate the drawbacks of the prior art described above (i.e., make the amount of incident light that saturates the output signal of each hue of a solid-state image sensor using complementary colors the same as a result). It is about providing.

[Summary of the Invention] The present invention is characterized by clamping the scheduled period of the blanking period of the output signal of the solid-state image sensor and clipping the output signal at a predetermined level or higher. The runner-up was achieved by matching the saturation state of the output signal to the amount of incident light.

[Embodiments of the invention]

Hereinafter, the present invention will be explained using the drawings.

In the present invention, the output signals of Ye and ay are the signal amounts of Ye and Oy at the saturation incident light amount of W9. By pressing K s W , Ye as shown in FIG.

It was decided to make the saturated incident light amount of Oy the same and eliminate the color error. In addition, in FIG. 2, curve 1 is
Curves 2a and 5a are the same as curve 1 in Figure 1, and curves 2a and 5a correspond to curves 2.3 in Figure 1, respectively.

FIG. 3 is a block diagram of a primary color (B, R) signal generation circuit of a video camera having an embodiment of the signal processing circuit of the present invention. In the figure, 4 is a solid-state image sensor using complementary colors, and 5 to 7 are W, Ye, and C!, respectively. line to which the y signal is applied, 8.9 is the signal processing circuit of the present invention, 10.1
1 is a subtracter, and 12 and 13 are lines to which B and H primary color signals are applied, respectively.

As is clear from the figure, the circuit of FIG.
e, Oy times signal, signal processing circuits 8 and 9, respectively W
The signal amount is clipped at the saturated incident light amount, and the subtracter io
, ii.

As a result, the subtractor 10.11 uses the above-mentioned B==W−Ys, which does not cause color error even when the amount of incident light exceeds the saturation amount of W.
, R:'W-Oy0)fA It is possible to perform calculations without a difference. That is, it is possible to output an R signal to the lines 12 and 13, which is faithful to the color of the object.

Next, a specific example of the signal processing circuit of the present invention used in the circuit of FIG. 3 is shown in FIG. 4, and will be described.

In the figure, 21 is the power supply input terminal, and 22 is the power supply input terminal as shown in Figure 5 (
Xe or Oy output from the flexible image sensor 4 shown in a)
23 is a ramp signal input terminal as shown in FIG. 5(b), 24 is an output terminal, 25 is a clamp converter, 26 is a load resistor, 27 to 30 are fixed resistors, 3
1 is a capacitor, and 32 to 34 are transistors.

In FIG. 4, when a signal (a) is input from the input terminal 22 and a shifting signal (b) is input from the input terminal 23,
During the period when the clamp signal (b) is irregular, the transistor 34 is turned on, so the clamp capacitor 25 absorbs the difference between the input signal (a) at that time and the voltage at the terminal of the resistor 29 that is not the ground terminal. charged to a potential. As a result,
The pace potential of the transistor 620 after the high level period of the clamp signal (b) becomes a potential obtained by superimposing the potential of the signal (a) on the difference potential.

That is, as is clear from FIG. 5(a) and (1:l), during the scheduled blanking period of the signal (→),
By synchronizing the clamp signal (→), the black level of the signal (a) can be always clamped to a constant potential, and fluctuations in the input signal (al) can be prevented. .

Next, if the base potentials of the transistors 32.55 are Vb+ and Vb2, respectively, and the saturation voltage drop between the base and emitter of both transistors 32.33 is Vf, then V
b+ 〉Vb 2 + Vf Under the condition, the emitter voltage of both transistors 32.33 is 'hv2-f-Vf
As a result, the transistor 620 becomes reverse biased between the emitter and the transistor 32, so that the transistor 32 is turned off. That is, the transistor 32 has Vl<; Vb2
Only the +Vf O) range is in operation. Therefore, the output signal 24 of the circuit shown in FIG. 4 is equal to or greater than the potential Vbz'+ of the transistor 32, that is, the signal (a) Vb2+Vf.

That is, if the Vb2+Vf is set to the same potential as the saturation direct pressure of the output signal with respect to the amount of incident light of W, the circuit shown in FIG. 3 can clip the output signals of Ye and Oy to the saturation potential. become.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the output signals of the solid-state image sensor, for example, Ye and cyC/), are determined by the signal amounts of Ye and Cy at the saturated incident light amount of W9. As a result, the saturation incident light amounts of W, Ye, and ay can be made the same, thereby eliminating color errors.

That is, according to the present invention, it is possible to eliminate the difference in the amount of incident light that saturates the output signal of a solid-state image sensor using complementary colors in the signal processing subsequent to the image sensor.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram showing an example of the incident light amount-output signal characteristic of the image sensor, and FIG.
6 is a diagram of the incident light amount-output signal characteristic of the image sensor corresponding to the figure, FIG. 6 is a diagram of a primary color signal generation circuit of a video camera having an embodiment of the signal processing circuit of the present invention, and FIG. 4 is a diagram of the present invention. FIG. 5 (a) is a circuit diagram showing a specific example of the signal processing circuit of
) and (b) are waveform charts (time charts) of the input signal and clamp signal applied to the two input terminals of FIG. 4, respectively. 21.22.23... Input terminal, 24... Output terminal, 25... Clamp capacitor, 26... Load resistance, 27-30... Fixed resistance, 31... Capacitor,
32-34...transistor. /''j4'a A Shimabori J 94=JL +, -t・'
Figure 7 Go to Figure 2

Claims (2)

[Claims] (1) A signal processing circuit comprising clasp means for clamping a scheduled blanking period of an output signal of a solid-state image sensor, and clipping means for clipping a predetermined level or more of the output signal and outputting the clipped signal. . (2) The clasp means and the clip means are first and second PNPs having both emitters connected, the connection point being connected to a power supply via a load resistor, and both collectors being grounded. a transistor, a resistor disposed between the base of the first transistor and the power source, two resistors connected in series and disposed between the base of the first transistor and ground; , a third transistor connected to the connection point of the two resistors, having its collector connected to the base of the second transistor via the resistor, and having its base connected to an input terminal to which a clamp signal is applied; The signal processing according to claim 1, characterized in that the signal processing comprises an input terminal to which an output signal of a solid-state image sensor is applied and a clamp capacitor disposed between the base of the second transistor. circuit