ZR36050

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The ZR36050 is a high-speed JPEG Image Compression Processor that performs the algorithm specified by the JPEG Baseline and JPEG Lossless standards for high-quality image compression and expansion of continuous-tone color or monochrome images. The ZR36050 performs Discrete Cosine Transform (DCT), quantization and variable-length encoding for image compression (coding), and the corresponding inverse operations for expansion (decoding).

In the JPEG Baseline encoding operation, the ZR36050 performs the DCT operation on 8 x 8 blocks of image data, converting image data into its spatial frequency components, and quantizes them using a user defined "quantization table." Because the human visual system is less sensitive at the higher spatial frequencies, these higher frequency components can be uantized more coarsely than the lower-frequency components, with negligible effect on image quality.

The coarser quantization of high-frequency coefficients results in long strings of zero valued quantized coefficients, when the 8x8 blocks are scanned in zigzag order. The scanned coefficients are characterized in terms of their nonzero values and the zero run lengths. As a result, a long string of zeroes is coded as a single number. The ZR36050 then performs Huffman coding using user-defined Huffman tables, whereby bit patterns of different lengths code the nonzero values (values that occur frequently use the shortest codes; while those that infrequentlyoccur use the longest codes). These techniques greatly reduce the amount of memory needed to store an image.

In the decoding operation, the compressed data of ZR36050 is decoded (the inverse of the Huffman and the zigzag modified-run-length coding), and dequantized. A 2-D inverse Discrete Cosine Transform is performed on the DCT coefficients, resulting in an expanded image.