HISTOGRAM/VARIANCE MECHANISM FOR DETECTING PRESENCE OF AN EDGE WITHIN BLOCK OF IMAGE DATA

摘要

An edge detection mechanism for an imagery signal compression and transmission system processes histogram and variance data to identify the presence of a uniform area with a block of transform signals. The presence of an edge within an image block, for which corresponding transform coefficients are obtained, is identified by initially generating a histogram of the image block. If the maximum value of the histogram exceeds a first threshold value, a uniform area is inferred, and adaptive quantization that would otherwise be carried out prior to executing a minimum redundancy encoding scheme is bypassed. If the maximum value of the histogram does not exceed the first threshold value, a set of variance calculations is carried out for use with a further sequence of edge detection decisions. The total variance and low frequency variance of the block are determined in accordance with the transform coefficients associated with the image block. The results of these variance calculations are then processed with further thresholds and the histogram maximum value. If the absence of an edge is inferred, the transform coefficients associated with the image block are quantized using adaptive quantization.