Automatic gain control method and device for CVBS (Composite Video Broadcast Signal)

Abstract

The invention discloses an automatic gain control method and device for a CVBS (Composite Video Broadcast Signal). The method comprises the steps of receiving a CVBS, and performing translation to obtain a translation signal of which the back porch is a 0-based signed number; multiplying the translation signal by an automatic gain value to obtain an amplified signal; solving the feature level of the amplified signal, acquiring a synchronous gain value and a peak gain value, performing filtration and amplitude limitation on the smaller value to obtain the automatic gain value, returning to the front step, and multiplying the translation signal by the automatic gain value. The acquired automatic gain value is more accurate by solving the feature level of the CVBS, and the method and the device is not only suitable for automatic gain control of normal CVBS but also suitable for automatic gain control of nonstandard signals, so that the overall watching effect of images is not influenced. In addition, automatic gain adjustment is quickly performed in view of the initial state during startup or plug-unplug of the system, so that images can reach the stable state more quickly, and long-time white or dark images do not appear.

Description

technical field [0001] The invention relates to the field of analog video signal processing, in particular to a CVBS signal automatic gain control method and device. Background technique [0002] CVBS (CompositeVideoBroadcastSignal, composite video signal), contains brightness information, color difference information (hue and saturation), and synchronizes them in the blanking pulse and transmits them with the same signal. CVBS is a relatively early display method, more precisely, it is the first generation (the second generation is S-VIDEO, the third generation is VGA, the fourth generation is DVI, and the fifth generation is HDMI) video display output method, However, since all video signals are included in one signal, only one transmission line is required, so compared with the interface signals that were developed rapidly later, CVBS is still the most important analog video input signal. [0003] CVBS is widely used in video doorbells, car rearview mirrors, car MP5, and...

AI Technical Summary

Problems solved by technology

[0004] During the CVBS transmission process, due to the characteristic impedance and attenuation index of the transmission medium itself, the transmitted signal will have a certain loss. The horizontal and vertical synchronous signals cannot be locked, and the decoding is wrong. This requires AGC (AutoGainControl, automatic gain control) to amplify the input CVBS signal to a normal amplitude before finally implementing subsequent video processing.

[0005] Due to the nonlinear characteristics of the transmission system, it may also cause the attenuation between the synchronous signal amplitude and the overall signal amplitude of the CVBS signal not in accordance with the standard ratio. It is possible that the synchronous head is too small, but the overall signal amplitude is unchanged or too large. This is also the most common non-standard signal in CVBS signals. According to the usual method, when the synchronization height becomes smaller, the signal will be amplified to the reference synchronization height by increasing the AGC gain, but this will lead to The signal white level overflows, and the image is white and distorted

Another method is to simply lower the white level of the signal when this non-standard situation is detected, but this will also reduce the black level accordingly, causing the black level to overflow

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