Abstract: A method and a system for compressing a delta modulation coded bit string by logically adding together, in mod 2 fashion, adjacent string bits to generate a transformed bit string which is then runlength encoded to provide a compressed bit string. A second embodiment of the invention uses an alternate bit complementation transform which is based on complementing every alterate bit of the bit string to provide a transformed bit string which is then runlength encoded to provide a compressed bit string. Decoding is accomplished by inversing the encoding methods.

Abstract: In a differential pulse code modulation scheme incorporating a differential pulse code modulation encoder and decoder a reconstructed value constrainer is interposed in the signal path feeding the traditional predictor circuits. The reconstructed value constrainer selectively limits the values that a reconstructed signal may assume in order to provide the predictor circuits with values that are system realizable prior to processing.

Abstract: A system for compressing and transmitting a digital image signal over a limited bandwidth communication channel, transform codes the image values and quantizes the transform coefficients according to a two-dimensional model of the sensitivity of the human visual system. The model of the human visual system is characterized by being less sensitive to diagonally oriented spatial frequencies than to horizontally or vertically oriented spatial frequencies, thereby achieving increased compression of the image.

Abstract: In a method and apparatus for transmitting a digital image over a limited bandwidth communication channel, an image is block transformed to produce blocks of transform coefficients; the transform coefficients are quantized in accordance with a model of the visibility of quantization error in the presence of image detail; the quantized coefficients are encoded with a minimum redundancy code; and the coded, quantized transform coefficients are transmitted.

Abstract: A still image communication system performs a block cosine transformation on an image of bandwidth compression. A transmitter subsamples a full resolution image, to provide a preview image, and transforms and transmits the preview image prior to transforming and transmitting the full resolution image. A receiver and displays the preview image, and replaces the preview image on the display block-by-block as the full resolution is received.