DCT transform compression, transmission and recovery of digital color using virtual filtering mechanism

摘要

A color imagery compression/decompression mechanism employs a contrast sensitivity function model of the human visual system for color images, to derive normalization values for compressing chromatic components of the color imagery data. The CSF model is defined in terms of an ADT color space transform (15), the chromatic channels of which conform with the band-limited sensitivity of the visual system. The transform for obtaining the ADT components is executable by reduced complexity logic operators. Each of the ADT components is block transform coded using DCT transform coefficients (18) that are normalized (24) in accordance with a `weighted` (46, 45) CSF model (42) of the human visual system, which effectively performs a low pass filtering of the chromatic (DT) channels. This low pass filter-weighting of the normalization values in the compression, transmit end (10) of the system produces a set of normalized coefficients which effectively blur the image and reduce the entropy in the chromatic channels and may be implemented using a Gaussian function. In the decompression process at the receiver (14), a corresponding set of denormalization coefficients (32), which are generated in accordance with the same chromatic CSF model of the human visual system, are not weighted, so that the cascading of the normalization and denormalizing operators in the transmitter and receiver yields a product less than unity, simulating the entropy-reducing effect of subsampling.