LYCOS RETRIEVER 
Entropy Encoding
built 655 days ago
The Entropy Encoding process divides the quantized sub-bands into rectangular code blocks. The Bit-Plane Coder categorizes each bit in the code block coefficient into 3 coding passes, each bit belonging to only one coding pass. It then parses the code block bit plane from most significant bit (msb) to least significant bit (lsb) and arranges the bits in a zigzag order for each bit plane. The Entropy Encoding process ... computes the context information needed by the MQ Coder as well as the distortion metrics that will be used by the rate allocation unit of the Tier-2 Coding process. The bits and contexts output from the Bit-Plane Coder are then processed by the MQ Coder that generates the compressed bitstream.
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Entropy Encoding After the quantized numbers are read out of the 8x8 matrix in a linear fashion, Run-Length Encoding (RLE) crunches consecutive zeros together (e.g., 0000000000 = 0 times 10). After RLE, repetitive patterns in the data stream may be replaced with abbreviations (MPEG imposes a fixed Huffman table, JPEG provides other choices).
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Perform optimization of entropy encoding parameters. Without this, default encoding parameters are used. -optimize usually makes the JPEG file a little smaller, but cjpeg runs somewhat slower and needs much more memory. Image quality and speed of decompression are unaffected by -optimize.
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Entropy Encoding