Abstract: A method of bit rate control and block allocation for discrete cosine transform (DCT) image signal compression includes the steps of (a) partitioning the image signals in blocks representing portions of the total image, (b) calculating DCT coefficients for image data in all blocks, (c) obtaining a measure of block activity (BACT) for each block based on DCT coefficients and for the total image activity (ACT) as a sum of the measures of all block activity, and (d) determining a code allocation factor (AF) for each block based on the ratio of block activity (BACT) to target code volume (TCV data) for the coded image data. Thereafter, step (e) includes allocating bits for each block using the allocation factor (AF) for each block and the target code volume (DCV data).

Abstract: Disclosed is an image compression coding device in which time domain image data is transformed to frequency domain data and then compressed by multiplying the frequency domain data by quantization coefficients scaled by a scale factor based on a non-linear relationship of log(ACVdata) versus log(SF). One or more statistical passes are made through the frequency domain data using initial scale factors in which ACV data is obtained based on the newly defined relationship. The New Scale Factor (NSF) is then calculated based on the initial scale factors (ISF1, ISF2), the accumulated code volumes for the two scale factors (ACVdata1, ACVdata2), and the target code volume (TCV) of the compressed file.

Abstract: Encoding and decoding speed in using DCT and IDCT algorithms is enhanced by parallel operation of coding and decoding devices. A frame of image data can be vertically sliced with each slice operated on by a dedicated encoding device and with the encoded slice data concatenated to form the encoded frame of data. Decoding speed is increased by using a plurality of decoding devices in parallel with each decoder having a Huffman decoder and a coefficient dequantizer through which all coded data flows. Only assigned blocks of data are operated on by the IDCT unit in each decoder. Each decoder device can have a plurality of IDCT units for operating on assigned blocks of data.