Controllable pseudo random noise pattern generator for use in video

Abstract

A pseudo-random pattern generator has modifiable feedback so that a variety of pseudo-random video patterns can be generated and used either directly, or after further manipulation, to control the mixing of two video sources. Control of a multiplexer allows a variety of pattern lengths to be selected by altering which stages of a shift register are supplied to a feedback exclusive-OR gate. Patterns with controllable granularity can be achieved by stretching each part of the noise pattern a selectable number of times along either or both axes. Horizontal stretching is achieved by clocking the shift register more slowly than the rate at which it is being read out. Vertical stretching is achieved by repeating the same pattern on each of a selectable number of consecutive lines. Varying the ratio of the stretching along the horizontal axis to the stretching along the vertical axis allows the aspect ratio of the grains of the pattern to be controlled. The values that are used to initialize the shift register can also be altered to achieve additional variation in the patterns generated. Two (or more) modifiable pseudo-random pattern generators can be used in combination with an array of selectable filters to provide a controllable noise pattern generator with coarse and fine pattern controls and selectable filtering of the output patterns produced.