US 7,443,455 B2 · Automatic gain control based on multiple input references in a video decoder

Abstract

A video decoder (10) for receiving an input video signal and producing output signals for a digital display (12), and involving automatic gain control (AGC) functions (20, 28), is disclosed. For each of the front-end and back-end AGC functions (20, 28), the AGC gain value applied is modified according to measurements of several attributes of the video signal, such as sync height, color burst amplitude, composite signal peak amplitude, and luma signal peak amplitude. The measurements are made, and the AGC gains are modified, on a frame-by-frame basis. Preferably, the AGC is modified using the one of the signal attributes that indicates the lowest gain. The back-end AGC function (28) modifies its gain to unity if the front-end AGC function (20) selected the luma signal peak amplitude for modifying its gain. A method for adjusting the rate of change of the AGC gain is also disclosed, in which gain increases are delayed and slowed following an AGC gain decrease because of an image-dependent signal attribute.

Claims19

Dependent claims

A video decoder, comprising:

input interface circuitry for receiving an input video signal;
separation circuitry, for separating the received input video signal into signal components;
output format circuitry for presenting an output signal to a video display;
a first automatic gain control circuit, having an output coupled to an input of the separation circuitry, and comprising:
a gain stage for amplifying a signal corresponding to the input video signal by a first gain value;
and gain update circuitry, for modifying the gain value responsive to a selected one of a plurality of signal attributes of the input video signal;
and
a second automatic gain control circuit, having at least one input coupled to a corresponding output of the separation circuitry, and comprising:
at least one gain stage for amplifying a signal corresponding to the output of the separation circuitry by a second gain value;
and gain update circuitry, for modifying the second gain value responsive to a selected one of a plurality of signal attributes of the input video signal.

7 more elements

Dependencies are inferred from the claim text.

Automatic gain control based on multiple input references in a video decoder

Life of this patent

Automatic gain control based on multiple input references in a video decoder

Life of this patent

Abstract

Claims19