JPS60171888A - Color television image pickup device - Google Patents

Abstract

PURPOSE:To obtain an excellent picture quality in matching with the illuminance of an object by detecting the decrease in a signal level at a low illuminance to make a base clip amount of a low saturation clip circuit suitable. CONSTITUTION:An image pickup element 6 converts optical information inputted through a lens 4 and an iris 5 into an electric signal and applies it to a variable gain amplifier 7. An operational amplifier circuit 8 obtains a luminance signal Y and color difference signals R-Y, B-Y from an image pickup element output and supplies the result to modulators 1,2. The color difference signals after modulation is fed to a low saturation clip circuit 12. The low saturation clip circuit 12 detects the decrease in the output of a detection circuit 10 and decreases the base clip amount and sets the value to an optimum value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a color television imaging device that provides suitable image quality for all subject illuminances.

[Background of the invention]

Conventionally, in color television imaging devices, base clipping processing has been performed on color difference signals in order to reduce color unevenness caused by distortion and non-uniformity of an imaging element.

The effects and drawbacks of this color difference signal base clipping process will be explained below using a single-tube frequency-separated color camera as an example. The single-tube frequency-separated color camera is currently one of the mainstream imaging devices because of its small size and light weight.

A single-tube frequency-separated color camera uses two types of stripe filters (generally a cyan stripe filter and a yellow stripe filter) installed on the imaging surface to generate two color signals (generally red and blue signals) in the form of modulated waves in the luminance signal. ) is extracted as a modulated multiplex signal. In this case, the degree of modulation of the color signal changes depending on the position of the imaging surface, which causes color unevenness called shading. Furthermore, since the degree of modulation of the color signal changes depending on the brightness level, color unevenness also occurs due to tracking deviation between the brightness signal and the color signal. .

In order to remove these color irregularities, shading correction and tracking correction (De
−γ correction) is performed. However, these corrections are currently not sufficient, and residual color unevenness is a cause of image quality deterioration. This residual color unevenness is more noticeable in low chroma areas where the color difference signal is small than in high chroma areas, and appears as unsightly coloring, especially in achromatic areas.

In order to prevent coloring in the achromatic portion, base clip processing is performed on the color difference signal to clip small signals.

There are various methods for similar 1 clipping, as follows: 1) Base clipping is performed for each of the color difference signals (R-Y) and (B-Y).

2) Low saturation is detected using the color difference signals (R-Y) and (B-Y), and the gain of the color difference signal is lowered using this detection signal.

5) After orthogonally modulating the color difference signals (R-Y) and (B-Y), base clipping is performed on the modulated signals.

Here, the method (3) above, which has a simple and common circuit, will be explained with reference to FIGS. 1 and 2. In FIG. The color difference signals (R-Y) and (B-Y) obtained through the processing are sent to the modulator 1, respectively.
．． 2 and has a phase difference of 90°.
, SC2. After modulation, the added signal is subjected to low saturation clipping by a low saturation clipping circuit 3. Thereafter, a standard television signal is synthesized from the signal obtained by this signal processing and the luminance signal.

At this time, the low saturation clipping circuit 5 is configured, for example, as shown in FIG.
), and when the modulation signal shown in (a) of the same figure is input to the low saturation clipping circuit 3, as shown in (e) of the same figure, A signal with low chroma portions cut is output.

As a result, coloring of the achromatic portion is prevented, and image quality can be improved.

However, while the conventional low saturation clip as described above has the above-mentioned effects, it also has the following drawbacks.

Conventional low-saturation clips are set so that good image quality can be obtained with standard subject illumination where the signal level is maintained appropriately. Therefore, when the illuminance of the subject decreases and the overall signal level decreases, the color difference signal also decreases, and there are many areas where colors disappear on the screen due to low saturation clipping, and the saturation level decreases overall. For this reason, there was a drawback that an image with poor coloring and lack of clarity was output.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a color television imaging device t that eliminates the drawbacks of the prior art described above, performs appropriate low chroma clipping for any subject illuminance, and provides good image quality.

[Summary of the invention]

The present invention detects a luminance signal obtained from an image sensor, uses this detection voltage to detect a decrease in signal level at low illuminance, and optimizes base clipping in a low saturation clipping circuit. There are characteristics.

[Embodiments of the invention]

Examples of the present invention will be described below with reference to FIGS. 5 and 6.

FIG. 3 shows a block diagram of one embodiment of the invention. Third
In the figure, 4 is a lens, 5 is an iris, 6 is an image sensor, 7 is a variable gain amplifier, 8 is an operational amplifier circuit, 9 is an encoder, 10 is a detection circuit, 11 is an iris drive circuit, 12
is a low saturation clipping circuit.

First, the image sensor 6 converts optical information input through the lens 4 and iris 5 into an electrical signal, and supplies the electrical signal to the variable gain amplifier 7. The variable gain amplifier 7 amplifies the image sensor output to an appropriate level, and the detection circuit 10 and the operational amplifier 8
supply to.

In the operational amplifier circuit 8, the luminance signal Y and the color difference signal (R-Y), ('B-Y) are synthesized from the standard television signal by calculation from the image sensor output amplified to an appropriate level.
, the luminance signal Y is supplied to the encoder 9, and the color difference signal (
R, -Y).

(B-Y) are respectively supplied to the modulator 1.2. The modulator 1.2 modulates the color difference signals (R-Y) and (B-Y) supplied by the operational amplifier 8 using subcarriers SCI and SC2 having a phase difference of 90°, respectively. The modulated color difference signals are added together and supplied to the low saturation clipping circuit 12.

The detection circuit 10 extracts a luminance signal from the output of the image sensor that has been amplified to an appropriate level by the variable gain amplifier 7, and detects this luminance signal. The detection output is output from variable gain amplifier 7.
The signal is supplied to the gain control terminal of , the iris drive circuit 11 and the low chroma clipping circuit 12 . At this time, variable gain amplifier 7
, the detector 10 , the iris 5 , the image sensor 6 , the variable gain amplifier 7 , the detector 10 , and the iris drive circuit 11 each constitute a control loop, and in the operating region, the overall signal level (peak value or average value) ) is kept constant. At this time, the detection output also shows a constant value.

Generally, an iris control loop and a variable gain amplifier 7
The operating range of the control loop (hereinafter referred to as AGC) consisting of the detector 1o and the wave detector 1o is as shown in FIG. In FIG. 4, the horizontal axis represents the amount of incident light, and the vertical axis represents the signal level.

At low illuminance, there is a region A in which AGC does not operate even if AGC is at its maximum. In this region A, the signal level decreases and the detection output decreases. The low saturation clip circuit 12 of this embodiment detects this decrease in the detection output, reduces the base clip amount, and sets the base clip amount to an optimal value.

At this time, the base clip amount is changed, for example, as shown in FIG. In Fig. 5, a is the input/output characteristic of the low saturation clipping circuit 12 at standard time, and b is the input/output characteristic at low illuminance. An example of the saturation clipping circuit 12 is shown. This circuit is a voltage-controlled variable base clipping circuit, where a in FIG. 6 is an input terminal 7b and an output terminal, and C is a control terminal for the amount of base clipping.

The operation of the variable base clip circuit will be explained below.

In FIG. 6, Q1-Q11 are transistors, R1-
R11 is a resistor, and E1 to E3 are DC power supplies.

Here, the pair of transistors Ql and Q2. Q3 and Q4. Q7 and Q8 and Q9 and Q10 are all assumed to have the same characteristics, and furthermore, in terms of resistance, R1=R2,
The relationships are as follows: R5=R6, R7=R8, and R9=R10. Further, the potential of the DC power supply E5 is made equal to the reference level (θ level) Va of the color difference signal (RY or BY signal) input from the input terminal a.

First, the control voltage Vci is supplied to the input terminal C. As a result, a current 1 (Vc) corresponding to this Vc flows through the transistor Q10, and as described above, by making the characteristics and resistance values of the paired Tr equal, the transistor QB,
An equal current 1 (Vc) flows through Q7 (Q7 and Q8 constitute a current mirror circuit) and Q9. Therefore, transistor Q2. Q4 (7) Pace potential ■b2
．． vb4c is as follows.

Vb2=Vs+1(Vc); R7Vb4=
Va -1(Vc) ・R8Here, since R7=R8, R7-1(Vc)=i(Vc)・R8=ΔVo(
Vc). Therefore, Vb2=Vs+ΔVo(V
c), Vb4 ==Vs-ΔVo (Vc).

Next, the color difference signal Vin (Vs+v) is input to the input terminal a. Here, transistors Q5 and Q6 are each
Constant bias current, transistors Q1 and Q2. Q3 and Q
It functions to flow to 4. Further, transistors Q1 and Q2 and Q3 and Q4 function as comparators and perform switching operations.

Now, transistor Q1. Since Q2 is an NPN type transistor, the transistor with a higher base potential is turned on, and the emitter potential is lower than the higher pace potential by the base-emitter voltage Vbe (when on, it is approximately constant at around 0.6 V). ). Also, transistor Q3:
, Q4 are PNP transistors, so the transistor with the lower pace potential is turned on, and the emitter potential becomes higher than the lower pace potential by Vbe.

Now, assuming that the emitter potentials of transistors Q1 and Q2 and Q3 and Q4 are fVe1+Vez, their respective values are as follows.

Furthermore, the pace potential Vb++ of transistor Q11 is
Since R1=R2 and the currents flowing through the nuclear resistors R1 and R2 are small, the equation is as follows.

Vb++ = (Vel +Ve2)/2 Therefore, the output potential Vout of the terminal is as follows.

The signal component ΔVout(”V
Out −Vs +Vbe ) f Considering this, the signal component ΔVout is as follows.

In addition, in the above equation l, the conditions of each equation on the right side, that is,
The conditions in parentheses are V'i n = v +Vs,
Vbz=Vs+ΔVo(Vc)+Vb4=Vs−Δ
Considering Vo(Vc) f, it can be easily derived.

Now, looking at the conditions for ΔVout = 0 in the above equation, ΔVo (vc) > v > -ΔVo (Vc). Moreover, when the control voltage vc becomes smaller, 1ΔVo(
Vc) l becomes smaller. Therefore, when the illuminance becomes low and the control voltage V'c decreases, 1ΔVo(Vc) l
The range in which Δvo1]t is clipped, that is, v<lΔVo(Vc) l, also becomes smaller.

[Effects of the Invention] According to the present invention, it is possible to perform appropriate low saturation clipping in accordance with the illuminance of the subject in a color television imaging device, and it is possible to record a good image quality that matches the illuminance of the subject. There is.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional low chroma clipping circuit, FIG. 2 is an input/output characteristic diagram of a conventional low chroma clipping circuit, and FIG. 3 is a block diagram of an example of the present invention. FIG. 4 is a diagram showing the signal level for incident light, and FIG. 5 is a diagram showing the signal level for incident light.
Figure 6 is a circuit diagram showing a specific example of the low saturation clipping circuit. 1.2 Modulator 5 Iris 6 ...Image sensor 7...Variable gain amplifier 8...Operation amplifier?・
... Encoder 10 ... Detection circuit 11 ... Iris drive circuit 12 ... Low saturation clip circuit Patent attorney Akio Takahashi Figure 4 Figure S Tank Figure 6

Claims (2)

[Claims] (1) A color television imaging device includes a detection circuit that detects a DC voltage according to the illuminance of the imaging surface from a luminance signal obtained from an image sensor, and a detection output signal of the detection circuit to control the amount of base clipping of the color difference signal. 1. A color television imaging device comprising: a low chroma clipping circuit; the base clipping amount of the low chroma clipping circuit is changed in accordance with the illuminance of an imaging surface. (2) A patented color television imaging device characterized in that the amount of pace clipping of the low saturation clipping circuit is completely reduced as the illuminance becomes low.