JPS61212982A - Video camera signal processing circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a signal processing method for a bidet 1° camera that captures images even under low illumination.

[Background of the invention]

Home video cameras are used in dark places such as indoors.

Often used in places. When shooting under such low illumination, the level of the image signal obtained by the video camera is reduced, so the level of the image signal obtained by the video camera is reduced.

The reproduced image has a high SN ratio (signal-to-noise ratio).

It turns out to be very bad. Therefore, even when shooting under low illumination conditions such as indoors, the image quality is high.

It is desired that a reproduced image can be obtained.

Figures 4 and 5 show conventional video cameras.

A block diagram showing a signal processing method and its explanation.

This is an input/output characteristic diagram of the chroma correction circuit.

The conventional technology will be explained in more detail.

Figure 4 shows a conventional frequency separation method single-tube carabiner.

1 is a block diagram showing an example of a signal processing system of a video camera, in which 1 is an image pickup tube, 2 is a preamplifier, and 3 is an automatic gain control circuit (hereinafter referred to as an AGC circuit).

4.5 is a low-pass filter, 6 is a bandpass filter, 7 is a gamma correction circuit, 8 is an aperture correction circuit, 9 is an encoder, 10 is a color separation circuit, 11.12.14 is a color separation circuit.

Gamma correction circuit, 13 is a subtraction circuit, and 1 is an output terminal.

It is.

In FIG. 4, an image signal obtained from an image pickup tube.

The signal is amplified by a preamplifier 2 to a level suitable for signal processing and then supplied to an AGC circuit 3. A.

In the GC circuit 3, the supplied image signal is dark.

The level is due to being photographed in a bright place or in a bright place.

NTSC signal at a constant level even if there are fluctuations.

Level adjustment is performed to obtain the following. death.

The bell-adjusted image signal is passed through low-pass filters 4 and 5.

and bandpass filter B, respectively. .

The low-pass filter 4 separates the luminance signal. .

This brightness signal is the gamma of the television receiver.

Since the value is approximately 2.2, in order to correct this and reproduce an image with faithful gradation characteristics.

As shown in Figure 5, the gamma value is 045.

processed by a gamma correction circuit 7 having force characteristics.

The signal is supplied to the aperture correction circuit 8.

The aperture correction circuit 8 includes an image pickup tube and a receiver.

After being processed to correct the aperture effect caused by the finite scanning beam diameter and to reproduce an image with good resolution, it is supplied to the encoder 9.

On the other hand, it is modulated at a high frequency by a bandpass filter 6.

color signals are separated. This color signal is a color signal.

Separate circuit 10 for baseband red and green signals.

Separated. Each of these color signals is gamma supplemented.

It is led to the positive circuit 11.12, and the subtraction circuit after gamma correction.

13. And the cutoff wave number is IJ, 6
The low-band luminance signal separated from the image signal from the AGC circuit 3 by the low-pass filter 5 of MH2 is sent to the gamma correction circuit 1.
4, the above red light is detected by the subtraction circuit 16.

The signal is converted into a predetermined color difference signal between the signal and the blue signal, and then encoded into an NTSC signal by the encoder 9 and output from the terminal 15.

Incidentally, the image No. 1d obtained from the image pickup tube 1 depends on the amount of light received, and since the amount of light received differs between a dark place and a bright place, a difference occurs in the SN ratio of the image obtained by the image receiver. Since the image pickup tube 1 does not generate noise, the SN ratio of the video camera is determined by the level of noise generated by the preamplifier 2 itself and the level of the image signal obtained from the image pickup tube 1.

However, as mentioned above, in AGC circuit 3... is used to obtain a constant level NTSC signal.

Change the amplification factor according to the signal level from amplifier 2.

It is growing. Therefore, the brightness will be the same on the receiver.

Even if you can see it, the SN ratio when shooting in a dark place is.

Significant deterioration compared to when shooting in a bright place.

do.

Additionally, gamma correction has been applied to the low level parts.

Aperture correction signal with enhanced luminance signal.

is created, so the low level section has a poor S/N ratio.

min, i.e. the aperture in the part of the dark secret object.

Since the correction number becomes excessively large and the aperture correction of the luminance signal is performed using the aperture correction signal, G, and S
This had the disadvantage of causing a deterioration of the N ratio.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a signal processing method for a video camera that eliminates the drawbacks of the prior art described above and makes it possible to reproduce images with a good SN ratio even when shooting under low illumination.

[Summary of the invention]

・　4　・ To achieve this objective, the present invention uses low heat.

When shooting under the skin, black has a particularly poor signal-to-noise ratio.

Changes the gamma correction characteristics for areas close to the level.

This allows reproduction of images with apparently good S/N ratio.

It is distinctive in that it makes it possible.

[Embodiments of the invention]

Embodiments of the present invention will be explained below with reference to the drawings.

Ru.

FIG. 1 shows a signal processing of a video camera according to the present invention.

FIG. 1 is a block diagram showing an embodiment of a logical system, 1. .

1 is an image pickup tube, 2 preamplifiers, 3 is an A'GCl path, 4.
5 is a low-pass filter, 6 is a bandpass filter, and 7 is a low-pass filter.

Gamma correction circuit, 8 is aperture correction circuit, 9° is encoder 10 is color separation circuit, 11, 12.14 is.

Comma correction circuit, 16 is subtraction circuit, 15 output terminal, 1
6 is a control signal.

In the same figure, an image signal obtained from an image pickup tube 1 passes through a preamplifier 2, and is kept at a constant level by an AGC circuit 3.
A low pass filter 4 is processed to obtain a TSC signal.
, 5 and the bandpass filter B. Low-pass filter 4 is the brightness.

The signal is separated by gamma, which is the main part of the present invention.

Via a correction circuit 7 and an aperture correction circuit 8.

The signal is supplied to the encoder 9.

On the other hand, the low-pass luminance is separated by the low-pass filter 5.

The signal passes through a bandpass filter 6 and is separated by a color separation circuit 10.

The separated baseband red and blue signals are gamma correction circuits, respectively, which form the main part of the present invention.

After 11.12.14, a predetermined color difference signal is obtained by the subtraction circuit 1'5.

NTSC signal 7. .

〇 is output from terminal 15. Gamma correction circuit 7.11.12.14 is an AGC circuit.

As shown in FIG.

The gamma characteristics of the black level part are changed.

This control signal 16 is sent from the preamplifier 2 to A, G, C, and so on.

The slope of the black level portion is controlled to become smaller as the level of the image signal supplied to the circuit 3 becomes smaller. For this reason, when the level of the image signal is low, that is, when shooting in a dark place, the amplification factor of the black level portion with a poor S/N ratio becomes small or 0, so the image signal passes through the gamma correction circuit.

The signal-to-noise ratio of the signal is improved. Photographed in a darker location.

Then, the control signal 16 has a rough gamma characteristic slope.

Since the noise is reduced, the apparent S/N ratio deteriorates.

It can be kept small.

FIG. 3 is a circuit diagram showing one side of the gamma correction circuit shown in FIG. 1, which is the main part of the present invention.

The transistor TR1 forms an emitter follower with the resistor R+, and forms an emitter follower with high input impedance through the resistor fb in the subsequent stage.

A circuit consisting of a transistor Trt2, a resistor R7, and a power transistor is driven. The black level applied to the input terminal -J-17 of the gamma correction circuit is fixed at Eo, and if the image signal is a triangular wave as shown in the figure, when shooting in a bright place, the control signal 16 is set to El. Lower, FETTR3
There is no conduction. Note that the voltage of each constant voltage source is E+ <
It is in the N section where R2<R5<R4.

When the image level of the image signal applied to the input terminal 17 becomes higher than R2, the diode D2 becomes conductive and the TR
The image level of 82 or above of the image signal No. 7 supplied from the emitter No. 1 is divided by the resistor R2 and the resistor R4.

output which appears at the emitter terminal 18 of TR2.

force level is reduced. Furthermore, the image level is R5.

When the voltage becomes larger, the diode D3 becomes conductive, and the image level of the image signal supplied from the emitter of TR1 is divided by the resistor R2 and the parallel resistance of the resistors Ra and Rs, and the image level of the image signal higher than 83 becomes smaller. Become. When the human image level becomes larger than R4, the diode D4 becomes conductive, so the image level of 84 or higher is connected to the resistor R2 and the resistor R.
With a parallel resistance of 4HRs r.

be divided. As a result, the image signal of the first day at the output terminal becomes a signal obtained by subjecting the image signal applied to the input terminal 17 to gamma correction with gamma characteristics as shown in FIG.

By the way, when a photograph is taken in a dark place, the control signal 16 becomes slightly larger than El, causing TR3 to conduct. As a result, El is larger than Eo
For smaller image level signals, diode D1
conducts, and the resistor R2 is divided by the sum of the resistors R3 and TR3 according to the potential of the control signal 16 applied to the gate. As a result, as shown in the part where the input is less than 0.2 in Figure 2, the result is ga.

The slope of the timer characteristics becomes smaller. In an even darker place.

When photographing, the potential of the control signal 16 rises to T.

Since the conduction of R3 is improved, the resistance value of TR3 becomes smaller, as shown in FIG.

The slope of the gamma characteristic in the above portion becomes smaller. vinegar.

In other words, the gamma correction circuit according to the present invention is clear.

For shooting in bright places, use the regular 045 gamma.

However, when shooting in a dark place (1), that is, under low illumination, the potential of the control signal 16 of the AGC circuit 3 increases, and TR6'fi: conducts.

and then set the gamma value of the gamma characteristic to the second level depending on the darkness.
It can be changed as shown in the figure.

〔Effect of the invention〕

As explained above, according to the present invention, when shooting in a bright place, normal gamma correction is applied and S
When shooting in a dark place where the N ratio is poor, the slope of the black level part is reduced depending on the darkness, so the amplification factor of the black level part that makes the S/N ratio worst is reduced, and the visual effect is improved. This prevents a drop in the S/N ratio, making it ideal for use in dark places such as indoors.

Home video cameras are often used in difficult locations.

If applied properly, the signal-to-noise ratio will be sufficient even under low illumination.

It was obtained in good condition and is excellent except for the drawbacks of the above-mentioned prior art.

Provides signal processing methods for video cameras with advanced functions.

can do.

[Brief explanation of drawings]

FIG. 1 shows a signal section of a video camera according to the present invention. FIG. 2 is an input/output characteristic diagram of the gamma correction circuit according to the present invention, and FIG. 3 is an example of the gamma correction circuit according to the present invention. FIG. 4 is a circuit diagram showing the front side of the circuit according to the prior art. A block that explains the video camera's signal processing method. FIG. 1 and FIG. 5 show a gamma correction circuit in the prior art. FIG. 1... Image pickup tube 2... Preamplifier 3... AGC circuit 4.5... Low pass filter 21 flow... Bandpass filter 7, 11.12.14... Gamma correction circuit 8... Aperture correction circuit 9...Encoder 10...Color separation M circuit 13...Subtraction circuit

Claims (1)

[Claims] In a video camera signal processing method, the image pickup tube output is passed through an automatic gain control circuit, separated into a luminance signal and multiple color signals, and gamma correction is applied to each signal.
By changing the gamma characteristics of the gamma correction circuit for performing the gamma correction according to the signal level of the image pickup tube output, an image with a good SN ratio can be obtained even when shooting under low illumination. A video camera signal processing method characterized by: