JPH0514628Y2 - - Google Patents

Description

[Detailed Description of the Invention] The signal processing circuit of the imaging device of the present invention will be explained according to the following items.

A. Field of industrial application B. Overview of the invention C. Prior art D. Problem that the invention attempts to solve E. Means for solving the problem F. Effect G. Example [Figs. 1 to 3] a. Circuit configuration [Fig. Figure 1] b Circuit operation [Figures 2 and 3] H Effects of the invention (A Field of industrial application) This invention is a signal processing circuit for a new imaging device, especially the image of what occurs in the high-brightness part of an image. The present invention relates to a signal processing circuit for an imaging device having a chroma suppress function that compensates for color reproduction errors caused by color saturation.

(B Overview of the invention) The signal processing circuit of the imaging device of the present invention is a signal processing circuit of an imaging device that has a chroma suppression function that compensates for color reproduction errors caused by imager saturation that occurs in high-brightness areas of images. , In order to compensate for color reproduction errors without unnecessarily complicating the circuit configuration and causing concerns about phase, the chroma suppressor circuit is controlled by the output of the AGC detection section of the AGC circuit through which the luminance signal passes. and
In addition, chroma suppression processing is performed on the chroma signal that is not subjected to FM modulation. Therefore, according to the signal processing circuit of the imaging device of the present invention, the brightness is determined using the AGC detection section of the AGC circuit. Since the chroma suppression circuit is controlled by the detection signal, there is no need to provide a special means for detecting luminance just for chroma suppression processing.
The circuit configuration of the signal processing circuit of the imaging device can be simplified. Further, since the chroma suppress circuit performs chroma suppress processing on the unmodulated color difference signal, there is no possibility that phase shift will occur due to the chroma suppress circuit.

(C Prior Art) General home video cameras are generally equipped with an automatic exposure adjustment mechanism, and therefore, it is desirable to take pictures when there is a large difference in brightness within one screen, such as when photographing a person etc. in backlight. Sometimes the subject, such as a person, becomes dark because the background is too bright. Therefore, in high-end video cameras, exposure can be adjusted by, for example, annual operation. Therefore, in the case described above, if the exposure is adjusted so that the subject is photographed darkly using automatic exposure and is photographed brightly, saturation will occur in areas that are much brighter than the subject. When saturation occurs in this way, the ratio of the components of each color of the signal changes. This is because when each color is saturated in the same way, the color component ratio does not change, but some color components are so strong that they are saturated, but other color components are not saturated. Sometimes, the color component ratio in the saturated portion of the reproduced image will differ from the true color component ratio in that portion. That is, the color changes, or in other words, a color reproduction error occurs. Therefore, in areas where the brightness is too strong, it is recommended to reduce the saturation of the color signal (in other words, bring it closer to an achromatic color) to make the color reproduction error less noticeable.
It has been proposed in Publication No.-26979, etc.

The system introduced in the same bulletin is equipped with a level detection circuit that detects the level of a luminance signal, and also has a chroma signal in the signal path through which the carrier color signal is created by separately frequency modulating and synthesizing two color difference signals. A suppression control circuit is provided, and the control circuit is controlled by the output of the level detection circuit. The output level of the carrier color signal is made smaller as the level of the luminance signal increases, and when the luminance signal exceeds a certain level of the luminance signal as a threshold value, the control circuit through which the carrier color signal passes is activated. The gain is set to 0 so that the color signal level becomes 0 level (that is, an achromatic color).

According to such a device, when the brightness is too strong, it is possible to make the color achromatic and look whitish, rather than displaying a color different from the actual color, which may cause unnaturalness on the reproduced screen. There is no. It can be said that it is excellent in that respect.

(D. Problems to be Solved by the Invention) However, the above-mentioned conventional device has a problem in that a special circuit is provided for detecting luminance, which makes the circuit complicated.

In addition, the chroma suppress processing by the control circuit is
Since this is performed on a carrier color signal that is FM modulated and has a high frequency band, there is a risk that a phase shift may occur due to the chroma suppression control circuit. Therefore, in order to prevent the image quality from deteriorating due to the phase shift, a special phase compensation circuit must be provided, and there is also the problem that the circuit configuration becomes complicated.

The present invention was made to solve the above problems, and is a novel imaging device that can compensate for color reproduction errors without unnecessarily complicating the circuit configuration and without causing any concerns about phase. The purpose of the present invention is to provide a signal processing circuit of the type described above.

(E. Means for Solving Problems) In order to solve the above problems, the signal processing circuit of the imaging device of the present invention consists of an amplifier circuit and an AGC detection circuit that controls the gain of the amplifier circuit, and receives the luminance signal from the imager. automatically control the level of
It has an AGC circuit and a clip circuit that clips the output of the AGC detection circuit, and when the level of the luminance signal exceeds a predetermined value, a chroma suppress signal output from the clip circuit suppresses the two color differences from the imager. A chroma suppressor circuit that controls the amplitude of the signal is also included.

(Faction) Therefore, according to the signal processing circuit of the imaging device of the present invention, the luminance is detected using the AGC detection circuit of the AGC circuit, and the chroma suppression circuit is controlled by the detection signal, so that the chroma suppression processing is performed. Therefore, there is no need to provide a special means for detecting brightness, and the circuit configuration of the signal processing circuit of the imaging device can be simplified. Furthermore, since the chroma suppress circuit performs chroma suppress processing on the unmodulated color difference signal, there is no possibility that phase shift will occur due to the chroma suppress circuit.

(G Embodiment) [FIGS. 1 to 3] The signal processing circuit of the imaging apparatus of the present invention will be described in detail below according to the embodiment shown in the accompanying drawings.

(a) Configuration [Fig. 1] Fig. 1 shows an example of an embodiment of a signal processing circuit for an image pickup apparatus according to the present invention.

1 is an imager, 2 is an AGC circuit through which the luminance signal Y output from the imager 1 passes, and is composed of an amplifier circuit 3 and an AGC detection circuit 4;
provides automatic exposure adjustment function. The luminance signal Y that has passed through the AGC circuit 2 (and its amplifier circuit 3) is input to the adder circuit 6 of the color encoder 5.

7 is a gain-controllable amplifier circuit that amplifies the color difference signal R-Y; 8 is a gain-controllable amplifier circuit that amplifies the color difference signal B-Y; both amplifier circuits 7 and 8 are connected to a white balance circuit 9; controlled. The outputs of the amplifier circuits 7 and 8 are amplified by the gain-controllable amplifier circuits 11 and 12 that constitute the chroma suppressor circuit 10, and then the carrier color outputted from the carrier color signal forming circuit 13 that constitutes the color encoder 5. The signal is superimposed on the luminance signal by the adder circuit 6,
It becomes an NTSC video signal.

14 is a clip circuit constituting the chroma suppressor circuit 10, and 15 is an amplifier circuit which amplifies the output of the clip circuit 14 and controls the gain of the amplifier circuits 11 and 12 using the output. The chroma suppressor circuit 10 is controlled by the AGC detection circuit 4 of the AGC circuit 2.

(b Operation) [Figures 2 and 3] The luminance signal Y and color difference signals R-Y, B-Y output from the imager 1 are subjected to luminance adjustment processing by the AGC circuit 2 and the white balance circuit 9, and are then adjusted to white. After being balanced, it is input to the color encoder 5 and becomes an NTSC video signal.

The output of the AGC detection circuit 4 constituting the AGC circuit 2 is used not only for gain control of the amplifier circuit constituting the AGC circuit 2, but also for controlling the chroma suppressor circuit 10. Specifically, the output of the AGC detection circuit 4 is first input to the clip circuit 14. When the luminance signal is not particularly strong, the AGC detection output does not exceed the clip level. Note that the level of the AGC detection output decreases as the level of the luminance signal increases, and when the luminance signal exceeds a predetermined level, the level of the AGC detection output becomes lower than the clip level. It is expressed as exceeding the clip level.

As described above, when the AGC detection output does not exceed the clip level, the chroma suppress signal output from the amplifier circuit 15 is kept at 0 level, and the gains of the amplifier circuits 11 and 12 are kept at 0 [dB]. Therefore, the color difference signals are not chroma suppressed.

When the brightness signal becomes very strong and exceeds a predetermined level, the AGC detection output exceeds the clip level (goes below the clip level), and a chroma suppress signal is generated which becomes low in approximately correspondence with the strength of the brightness signal. Then, the gains of the amplifier circuits 11 and 12 are controlled by the chroma suppress signal.
FIG. 2 shows the relationship between chroma suppression and the gain of the amplifier circuits 11 and 12. When the chroma suppression signal is small, the gain is 0 [dB], but when the chroma suppression signal becomes large (i.e.,
When the brightness increases) the gain becomes negative [dB]
The color difference signals R-Y and B-Y are attenuated. When the luminance signal is very large, the color difference signals RY and BY may be completely cut off.

FIG. 3 is a time chart showing that a chroma suppress signal is generated corresponding to a portion where the luminance signal Y is strong.

In this way, the signal processing circuit of the imaging device shown in FIG. 1 detects when the luminance signal Y is too strong.
The AGC detection circuit 4 of the AGC circuit 2 detects the color difference signals R-Y, B by the chroma suppressor circuit 10.
-Y can be suppressed, thereby lowering the saturation of the color signal and bringing it closer to an achromatic color. Therefore,
Color reproduction errors become less noticeable, eliminating unnaturalness on the playback screen. Since chroma suppression is used, it is possible to reduce color reproduction errors even when the aperture is opened or the shutter speed is slowed down, and there is no need to carefully adjust the aperture to prevent the image from becoming saturated, unlike in general electronic cameras. There isn't.

Since chroma suppression is performed based on the output of the AGC detection circuit 4 of the AGC circuit that plays the role of automatically adjusting exposure, there is no need to provide a special circuit for brightness detection for chroma suppression. Therefore, chroma suppression can be performed without unnecessarily complicating the circuit configuration.

Then, a chroma suppressor circuit 10 is applied to a color difference signal that is not FM modulated and therefore has a low frequency.
Since chroma suppression processing is performed by , phase shifts are less likely to occur. Therefore, the chroma suppressor circuit 10
There is no fear that a phase shift will occur and the image quality will deteriorate due to this phase shift. Therefore, there is no need to provide a phase compensation circuit to prevent image quality deterioration due to phase shift.

Note that the color encoder 5 is not necessary if the luminance signal and color difference signal do not need to be converted into NTSC color video signals.

The signal processing circuit of the imaging device of the present invention can be applied not only to video cameras but also to electronic still cameras.

(H Effect of the invention) As is clear from the above description, the signal processing circuit of the imaging device of the invention consists of an amplifier circuit and an AGC detection circuit that controls the gain of the amplifier circuit. It has an AGC circuit that automatically controls the output of the AGC detection circuit, and a clip circuit that clips the output of the AGC detection circuit, and when the level of the luminance signal exceeds a predetermined value, the image is and a chroma suppressor circuit that controls the amplitude of two color difference signals from a color difference signal.

Therefore, according to the signal processing circuit of the imaging device of the present invention, the brightness is detected using the AGC detection circuit of the AGC circuit, and the chroma suppressor circuit is controlled by the detection signal, so that the brightness is specially controlled just for chroma suppress processing. There is no need to provide a means for detecting , and the circuit configuration of the signal processing circuit of the imaging device can be simplified. Further, since the chroma suppressing circuit performs chroma suppressing processing on the color difference signal in an unmodulated state, there is no fear that a phase shift will occur due to the chroma suppressing circuit.

[Brief explanation of the drawing]

The drawings show an example of the implementation of the signal processing circuit of the imaging device of the present invention. Fig. 1 is a circuit diagram showing the circuit configuration, and Fig. 2 shows the relationship between the chroma suppression signal and the gain of the color difference signal amplification amplifier circuit. Characteristic diagram shown, 3rd
The figure is a time chart showing the operation. Explanation of codes, 1...Image, 2...AGC
Circuit, 4...AGC detection circuit, 10...Chroma suppress circuit, 14... Clip circuit.

Claims (1)

[Scope of Claim for Utility Model Registration] An AGC circuit that automatically controls the level of a luminance signal from an imager, which is composed of an amplifier circuit and an AGC detection circuit that controls the gain of the amplifier circuit, and that clips the output of the AGC detection circuit. a chroma suppressor having a clipping circuit and controlling the amplitude of the two color difference signals from the imager by a chroma suppressing signal outputted from the clipping circuit when the level of the luminance signal exceeds a predetermined value; A signal processing circuit for an imaging device, characterized in that: