JPH0454073A - Back light correction circuit for color video camera - Google Patents

Abstract

PURPOSE:To attain back light correction while suppressing the color S/N by reducing the correction quantity of a color signal more than that of a luminance signal when a circuit gain is increased at back light correction. CONSTITUTION:A back light correction control signal from a back light correction switch 14 is fed to a comparator 8 for operation of an iris 2 and an AGC circuit 5 to increase the entire system gain. Since the gain of the entire system is increased, the S/N of the signal is deteriorated and the color S/N deterioration especially causes unpleasant observation. In this case, a back light correction control signal is fed to a color separation signal circuit section and an attenuator 7 attenuates the color signal only by a degree in matching with the amplified ratio at a pre-stage, then the color S/N is improved and the entire S/N is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a backlight correction circuit for a color video camera.

[Prior Art] Figure 2 is a block diagram showing the configuration of a backlight correction circuit for a conventional color video camera. In the figure, (1) is a lens, (2) is an aperture, and (3) is an image sensor. , which forms an image of the light emitted from the subject and converts it into an electrical signal.

(4) is an amplifier circuit that amplifies the output of the image sensor (3). (5) is an automatic gain control circuit (hereinafter referred to as "automatic gain control circuit").

(referred to as AGC circuit), (8) is color separation circuit, (8)
and (11) are comparators, and (lO) and (13) are integrators.

(9) and (12) are adders, (10 is a backlight correction switch, (15) is a reference voltage, and (16) and (17) are output terminals for luminance signals and color signals.

Next, the operation of the above configuration will be explained.

Light emitted from a subject is focused on an image sensor (3) by a lens (1) and converted into an electrical signal. This image sensor (3
) is amplified by the amplifier circuit (0) and then input to the color separation circuit (6) where it is separated into a luminance signal and a color signal.

At this time, the signal detected by the integrator (10) is transmitted to the comparator (
8), and the aperture (2) performs feedback control so that the output of the image sensor (3) is maintained at a predetermined value. Also 5, A
The output of the G C circuit (8) is detected by the integrator (13) and
, a feedback control is performed to maintain the gain of the AGC circuit (6) at a predetermined value through the comparator (11).

Here, the comparison signals input to the comparators (8) and (11) are obtained by adding the reference voltage (15) and the voltage of the backlight correction switch (14) by the adders (9) and (12). be.

Such control determines the brightness of the screen.

[Problems to be Solved by the Invention] Since the backlight correction circuit of a conventional color video camera is configured as described above, the circuit gain of the variable gain amplifier circuit becomes large during backlight correction, and noise becomes noticeable.
In the case of a single-chip complementary color camera with originally poor S/N, color S
There was a problem that the deterioration of /N was large.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a backlight correction circuit for a color video camera that can suppress deterioration of color S/N during backlight correction.

[Means for Solving the Problems] A backlight correction circuit for a color video camera according to the present invention has the following features:
The present invention is characterized in that the amount of correction of the color signal during backlight correction is configured to also reduce the amount of correction of the luminance signal.

[Function] According to the present invention, by reducing the correction amount of the color signal with respect to the luminance signal during backlight correction, deterioration of the color S/N is suppressed even when the circuit gain becomes large, and noise becomes less noticeable. It is possible to perform backlight compensation without using the camera.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described based on the drawings.

FIG. 1 is a block diagram showing the configuration of a backlight correction circuit for a color video camera according to an embodiment of the present invention. Since this is the same as the conventional example shown in FIG.

In Fig. 1, (7) is an attenuator, and when a backlight correction signal is input by the backlight correction switch (14),
The color signal output from the color separation circuit (8) is attenuated to reduce the amount of color signal correction relative to the luminance signal.

Next, the operation of the above configuration will be explained.

Light emitted from a subject is focused on an image sensor (3) by a lens (1) and converted into an electrical signal. This image sensor (3
) is amplified by an amplifier circuit (4) and then input to a color separation circuit (6) where it is separated into a luminance signal and a color signal. At this time, the signal detected by the integrator (10) passes through the comparator (8) and is feedback-controlled by the aperture (2) so that the output of the image sensor (3) is maintained at a predetermined value. There is. In addition, the output of the AGC circuit (6) is detected by the integrator (13),
Feedback control is performed through the comparator (11) to maintain the gain of the AGC circuit (6) at a predetermined value. here,
The comparison signals input to the comparators (8) and (11) are obtained by adding the reference voltage (15) and the voltage of the backlight correction switch (14) by the adders (8) and (12).

Next, the operation during backlight correction will be explained.

A backlight correction control signal from the backlight correction switch (14) is sent to the operating comparator (8) of the aperture (2) and the AGC circuit (8), increasing the gain of the entire system. In particular, the gain in dark areas is increased to clearly express the gradation of dark areas of objects in backlit areas.

Since the gain of the entire system is increased, the signal-to-noise ratio of the signal is degraded, and the color signal-to-noise ratio is particularly noticeable. At this time, at the same time, a backlight correction control signal is supplied to the color-separated color signal circuit section, and the attenuator (7) attenuates only the color signal to an extent commensurate with the rate amplified in the previous stage, thereby improving the color S/N. However, the S/N quality of the signal as a whole is improved.

In the above embodiment, a one-stage switch is used as the backlight correction switch (10), but a multi-stage switch may be used to perform correction in finer stages.

Furthermore, the same effect as in the above embodiment can be obtained even if a variable resistor is used instead of the switch so that the correction amount can be continuously varied.

[Effects of the Invention] As described above, according to the present invention, when the circuit gain increases during backlight correction, the color S/N can be improved by reducing the number of color signal corrections for the luminance signal. Backlight correction can be performed with less deterioration.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a backlight correction circuit for a color video camera according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of a backlight correction circuit for a conventional color video camera. (1)...Lens, (2)...Aperture, (3)...
Image sensor, (5)...AGC circuit, (7)...Attenuator, (14)...Backlight correction switch. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] (1) In the backlight correction circuit of a color video camera equipped with a variable gain amplification circuit that corrects the gain of both the luminance signal and the color signal during backlighting, the amount of correction for the color signal during backlight correction is set to be higher than the amount of correction for the luminance signal. A backlight correction circuit for a color video camera, characterized in that it is configured to reduce the amount of light.