JPH0568913B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a gamma correction device for a consumer video camera.

Conventional Structure and Problems In recent years, since video cameras are driven at low voltage or are processed digitally, various signal processing is performed after the output signal from the image sensor is gain controlled.

A conventional gamma correction device for a video camera will be described below.

FIG. 1 shows a block diagram of signal processing in a conventional video camera, in which numeral 1 represents an image sensor having a color filter attached to each pixel. 2 is a preamplifier (PRE, AMP) that amplifies the output signal of the image sensor 1
It is. 3 is a color separation circuit that separates the signal into three primary color signals (red, green, and blue) and matches the amplitude of each signal. A gamma correction circuit 4 performs gamma correction on the primary color signal obtained from the color separation circuit 3. 5 is an encoder that converts the γ-corrected three primary color signals into a TV standard signal.The output signal is made to have a constant amplitude with the gain control circuit (AGC) of 6, and the pedestal (PED) and synchronization signal are output with the MIX circuit 7. Additionally, it outputs standard television signals. The biggest selling point of a video camera is that it can capture images with good signal-to-noise ratio even in dark places. Normally, when gamma correction is performed, when the signal amplitude is large, it is suppressed, and when the signal amplitude is small, it is expanded, resulting in a 6 to 10 dB worse S/N. In order to improve this, in normal imaging conditions, when gamma correction is set to normal and the contrast range of the subject is narrow when imaging a dark place, gamma correction is set to be looser to prevent the deterioration of S/N. It is prevented.

Figure 2 shows the input/output characteristics of gamma correction. a is a characteristic without gamma correction, c is a characteristic in which gamma correction is performed starting from a dark area, that is, an area where the signal amplitude is small, and b is a characteristic in which gamma correction is removed in dark areas and gamma correction is performed in bright areas.

If the gamma correction is made as shown in Figure 2b, the contrast ratio will be large when a bright subject is imaged, so gamma correction will be applied to achieve a natural gradation, and when a dark subject is imaged, the contrast ratio will be high. Since it is not large, even if the gamma correction is made loose, the gradation will not be affected. Moreover, the S/N ratio does not deteriorate.

However, in the above configuration, the gain is controlled after performing various signal processing, so in order to ensure the dynamic range of the signal processing section,
The power supply voltage cannot be lowered. That is, it is difficult to reduce power consumption. When digitizing signal processing, the output signal of the image sensor is usually gain controlled, set to a constant amplitude, and A/D converted to perform digital signal processing. In this case, the gamma correction is the same when capturing a bright subject and when capturing a dark subject, so the S/
N had the problem of becoming worse.

Purpose of the Invention An object of the present invention is to provide a gamma correction device for a video camera that performs gamma correction after gain control of a signal obtained from an image sensor, and that does not cause deterioration of S/N when imaging a dark subject. shall be.

Composition of the Invention The present invention includes a circuit that performs gain control on a signal obtained from an image sensor, a superimposition circuit that superimposes the gain-controlled signal, and a DC signal that changes depending on the gain of the gain control circuit; This is a gamma correction device for a video camera that includes a gamma correction circuit that performs correction and a circuit that removes the DC signal after gamma correction. By superimposing a DC signal on the signal and changing the reference level for gamma correction, the gamma correction can be made looser and the S/N ratio can be prevented from deteriorating.

DESCRIPTION OF THE EMBODIMENTS FIG. 3 shows a block diagram of a gamma correction device for a video camera according to an embodiment of the present invention. In FIG. 3, 1 is an image sensor, 2 is a preamplifier, 3 is a color separation circuit, 4 is a gamma correction circuit, and 5
1 is an encoder, 6 is a gain control circuit, and 7 is an MIx circuit, which is the same as the configuration shown in FIG. 8
is a circuit that superimposes the DC signal on the three primary color signals color-separated by the color separation circuit 3; 9 is a clamp circuit that removes the superimposed DC signal in 8; and 10 detects the gain of the gain control circuit 6. , a correction signal generator that generates a DC signal.

The operation of the gamma correction device for a video camera according to this embodiment configured as described above will be described below.

When a sufficiently bright object is imaged with the image sensor 1, the amount of light incident on the image sensor 1 is controlled by the aperture of the camera lens, and the amplitude of the output signal of the image sensor 1 is at a standard level. Therefore, the gain of the gain control circuit 6 is standard, and the output of the correction signal generator 10 is zero. FIG. 4d shows the input/output characteristics of the gamma correction circuit. FIG. 4a shows the input/output characteristics when gamma=1. In the standard state, the black level of the signal is at the reference point P in FIG. 4, and gamma correction as shown in FIG. 4d is applied. The clamp circuit 9 is for removing the change when the DC value changes in the DC signal superimposing circuit 8. Next time a dark object is imaged, the aperture of the camera lens is opened, and the amplitude of the output signal from the image sensor 1 is below the standard level. Therefore, the gain of the gain control circuit 6 becomes larger than the standard, and the output of the correction signal generator 10 generates a DC signal. This DC signal is superimposed on the three primary color signals color-separated by the color separation circuit 3, so that the DC potential of the black level of the signal becomes the reference point Q in FIG. As is clear from the characteristics shown in FIG. 4, since the gamma correction at this time is gentle, there is little deterioration in S/N.

As described above, according to this embodiment, since the output signal of the image sensor is gain controlled, the dynamic range of the subsequent signal is small, and the power supply voltage can be lowered, resulting in lower power consumption. can.
The DC signal output from the correction signal generator 10 is made to increase proportionally as the gain of the gain control circuit increases. Further, the output of the correction signal generator 10 is 0 until the gain reaches a certain level from the standard, and when the gain becomes larger than that, the output DC signal is generated, and after that, the output becomes proportionally larger. You should do it.

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 5 is a block diagram of a gamma correction device for a digital video camera showing a second embodiment of the present invention. 1 is an image pickup element, 2 is a preamplifier, and the above structure is the same as that shown in FIG. The difference from the configuration shown in FIG. 3 is that digital signal processing is performed. 11 is a gain control circuit, 12 is an analog-digital converter, 13 is a color separation circuit, 14
is a DC signal superimposition circuit, 15 is a gamma correction circuit, 1
6 is a DC signal removal circuit, 17 is an encoder, 18
is a digital-to-analog converter, 19 is a microcomputer (CPU), and 20 is an integration circuit.

The operation of the gamma correction device for a video camera according to the second embodiment configured as described above will be described below.

When a sufficiently bright object is imaged with the image sensor 1, the amount of light incident on the image sensor 1 is controlled by the aperture of the camera lens, and the amplitude of the output signal of one image sensor is at a standard level. Color separation circuit 13
The integration circuit 20 integrates the signal obtained by adding the three primary color signals, detects the average value of the luminance signal, inputs the detection signal to the CPU 19, and compares it with the reference. If the input signal is smaller than the reference value, Gain control circuit 1
The gain of 1 is increased to control the average value of the luminance signal to a standard level. Therefore, when the amplitude of the output signal of the image sensor 1 is at the standard level, the gain of the gain control circuit 11 is at the standard level. At this time, the DC signal generated from the CPU 19 to the superimposing circuit 14 is zero. At this time, the black level of the signal is at the reference point P in FIG. 4, and is converted by the gamma correction circuit 14 into a characteristic as shown in FIG. 4d. Since the removal circuit 16 removes the DC signal superimposed at 14, in this case, no signal to be removed is generated from the CPU 19. The output of the removal circuit 16 is converted into a television standard signal by an encoder 17, and then digital-to-analog converted into an analog signal.

Next, when a dark object is imaged, the aperture of the lens is opened and the output signal of the integrating circuit 20 becomes smaller than the reference level, so the CPU 19 increases the gain of the gain control circuit 11 until it reaches the reference level. Based on this, a DC signal for the superimposing circuit 14 is output from the CPU 19, and the black level potential of the signal is moved to the reference point Q in FIG. As a result, in the gamma correction circuit 15, the fourth
It is converted into the characteristic shown in Figure d. This is because the gamma correction is looser, and there is less deterioration in S/N. When it becomes even darker, the CPU 19 generates a DC signal lower than the reference Q in the direction of the arrow, and the superimposition circuit 14 superimposes it. At the same time as the CPU 19 generates a DC signal to the superimposition circuit 14, a DC signal is generated from the CPU 19 in order to restore the shifted DC potential to its original value, and the removal circuit 16 adds the DC potential to restore the DC potential to its original value. . and encoder 1
7 converts it into a television standard signal, and a digital/analog converter 18 converts it into an analog signal.

As described above, according to this embodiment, in order to keep the accuracy of the digital signal constant, a gain control circuit is installed in front of the analog-to-digital converter, and even after gamma correction, it is possible to image a dark subject. It is possible to prevent deterioration of the S/N ratio.

Further, in the first embodiment, in order to restore the shifted DC potential after the gamma correction signal, the DC signal is restored using the clamp 9, but the DC signal may be restored by adding the DC potential.

Further, in the second embodiment, the removal circuit 16 may restore the DC potential using a clamp.

Effects of the Invention The gamma correction device for a video camera according to the present invention superimposes a DC signal that changes depending on a circuit that performs gain control on a signal obtained from an image sensor and the gain of the gain control circuit, thereby changing a reference potential for gamma correction. Therefore, when the S/N is poor, reducing the amount of gamma correction will improve the S/N when imaging a dark subject.
Deterioration of N can be prevented. Furthermore, since gain control is performed at the beginning of signal processing, the dynamic range of the signal can be ensured, and the power supply voltage can be lowered, resulting in less power consumption, which has great practical effects.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional gamma correction device for a video camera, Fig. 2 is a gamma correction input/output characteristic diagram, and Fig. 3 is a block diagram of a gamma correction device for a video camera according to the first embodiment of the present invention. , FIG. 4 is a specific input/output characteristic diagram of gamma correction of the present invention,
FIG. 5 is a block diagram of a gamma correction device for digital signal processing of a video camera according to a second embodiment of the present invention. 1... Image sensor, 6... AGC, 8... Superposition circuit that superimposes a DC signal, 4... Gamma correction circuit,
9... Clamp circuit, 10... Correction signal generator,
12... A/D converter, 14... Gamma correction circuit, 15... Gamma correction circuit, 16... DC signal removal circuit, 19... CPU.

Claims (1)

[Claims] 1. A circuit that performs gain control on a signal obtained from an image sensor, a superimposition circuit that superimposes the gain-controlled signal and a DC signal that changes depending on the gain of the gain control circuit, and when the input level is smaller than a certain predetermined value. is smaller than the gamma correction amount of normal gamma characteristics, and when the input level is larger than a certain predetermined value, a gamma circuit having normal gamma characteristics and the superimposed signal are input to the gamma circuit, and after gamma correction, the DC A gamma correction device for a video camera characterized by being equipped with a circuit for removing signals.