JPS5981978A - Video signal correcting circuit - Google Patents

Abstract

PURPOSE:To obtain a signal output with nearly the same quantity of light even when there is a large difference in the quantity of light between an object and other parts, by sampling low-level parts in a video signal and combining them after level correction. CONSTITUTION:The video signal applied to a terminal 1 is amplified by amplifying circuits 2 and 3 and applied to a conversion part 4. The conversion part 4 compares its level with a set level (b) to obtain a pulsed output (c). The output (c) is inverted into an output (d) by an inverter 6. The output of the circuit 2, on the other hand, is amplified 8 and then a high-level part in the signal is removed by a process circuit 10. The low-level signal (e) passed through this circuit 10 is applied to a mixer 14 through a buffer amplifying circuit 12. A processing circuit 11 removes a low level part in the output of an amplifying circuit on the basis of the output (d). The output (f) of the circuit 11 is applied to the mixer 14 through a buffer amplifying circuit 13. Consequently, the mixer 14 mixes the output (e) and (f) to generate a composite output (g).

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a television camera or a correction circuit for a video signal output from the camera.

The structure of the conventional example and its problems The contrast ratio of the output signal of the conventional television camera or the video signal that is its output is different in the same period of time for any subject, and the entire area in terms of level is subject to the feedback signal. .

Therefore, even if you change the depth of the feedback amount, when shooting in a place where extremely bright and dark areas occur (for example, when shooting a subject with a bright window), the contrast ratio between bright and dark areas can still be output. However, particularly dark areas end up feeling like they are painted black.

OBJECTS OF THE INVENTION The present invention eliminates these drawbacks and makes it possible to easily obtain almost the same information on the monitor screen as on other parts even if the subject is backlit.

Structure of the Invention The present invention detects backlight (low level) information in a signal, and corrects the signal information of the backlight portion using that information.

DESCRIPTION OF THE EMBODIMENTS The following will explain an embodiment of the drawings. 1 is a terminal to which a video signal is applied; 2, 12; 13 are buffer amplifier circuits; 3,
8. 9 is an amplifier circuit, 4 is a conversion unit that converts the output a of the amplifier circuit 3 into a pulse, which is also used for the setting level b applied to the terminal 5;
6 is the inverter, and the end is the low level output terminal, 10.11
is a process circuit, 14 is a mixer, 15 is an output terminal, 16
17 and 18 are terminals to which a gain control signal is applied, and terminals 17 and 18 are applied to a DC level control signal.

In this configuration, the video signal applied to terminal 1 is amplified by 1J in amplifier circuits 2 and 3 and applied to converter 4. At this time, in converter 4, the set level b applied to terminal 5
It outputs a pulsed output like C. Further, this output is converted to an output like d by the inverter 6.

On the other hand, the output of the converter 4 is added to the process circuit 10,
The circuit 10 is set to cut high-level signals applied to it, and the amplifier circuit 8.12 and the process circuit 10 are designed to correct low-level signals. That is, after the output of the amplifier circuit 2 is further amplified by the amplifier circuit 8, the output of the amplifier circuit 2 is amplified by the process circuit 10.
The high level areas in the signal are removed. The low level signal that has passed through the processing circuit 10 is applied to the mixer 14 through the buffer amplifier circuit 12.

In the process circuit 11, the output of the inverter 6 is also used.
The output of the amplifier circuit 9 is set to completely remove the low level range, and the output is applied to the mixer 14 through the buffer amplifier circuit 13.
The output of 4 is the output of q, which is the sum of the outputs of e and f.

In other words, extracting the low level part of the video signal,
By compositing with level correction, even if there is a large difference in light intensity between the subject and other parts, the signal output is almost the same amount of light. Note that the process circuit 11 is not required, and the amplifier circuit 9.13
Therefore, the signal may be amplified over the entire range, and the low level portion thereof may be sent to the mixer 14 and combined with the output of the amplifier circuit 12 for correction.

Effects of the Invention As explained above with reference to embodiments, the present invention detects backlight (low level) information in the video signal and corrects it using this information. Images with uniform contrast can be easily obtained regardless of the

[Brief explanation of drawings]

The figure is a block diagram of a video signal correction circuit in one embodiment of the present invention. 1... Video signal input terminal, 4... Conversion section,
1 o. 11...Process circuit, 14...Mixer.

Claims (4)

[Claims] (1) A video signal correction circuit comprising means for converting a video signal into a contrast ratio and separating it into two levels, high and low, and means for combining both levels after correcting at least the low level among the levels. (2) The video signal correction circuit according to claim 1, wherein the high level is corrected when the high level and the corrected level are combined. (3) The video signal correction circuit according to claim 1, which does not correct the high level when combining the high level and the corrected level. (4) The separation of the high and low levels of the video signal is performed by a circuit that separates the video signal into high and low pulses based on the contrast ratio, and a circuit that separates the video signal into high and low levels based on the pulse. Video signal correction circuit.