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Unformatted text preview: QM-CoderThe arithmetic coders used in JPEG, JPEG 2000 and JBIG are called QM-coder. It handles only binary strings or input and it is designed for simplicity and speed. It uses approximation for multiplication operation, fixed-precision integer arithmetic with renormalization of the probability interval from time to time. The main idea of the QM-coder is to classify the input bit as More Probable Symbol (MPS) and Less Probable Symbol (LPS). Before the next bit is input, the QM-coder uses a statistical model (using a context, typically a two-dimensional context of black and white pixel in an image) to predict which one of the bits (0 or 1) will be the MPS. If the predicted MPSbit does not match with the actual bit, then the QM-coder will classify this as LPS; otherwise, it will continue to be classified as MPS. The output of the coder is simply a stream of MPSor LPS, which are assigned probability values dynamically to be used by the simplified arithmetic coder. The decoder has only the knowledge of whether the next predicted bit is MPSor LPS. It uses the same statistical model as that of the encoder to obtain the actual values...
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This note was uploaded on 06/09/2011 for the course CAP 5015 taught by Professor Mukherjee during the Spring '11 term at University of Central Florida.
- Spring '11