A compression device which uses both run length encoding and statistical encoding. The run length encoding scheme uses a flag byte symbol which is disposed between a character signal and a run length symbol. The statistical encoding process uses multiple statistical encoding tables which are selected based upon previously occurring data.

Data compression using run length encoding and statistical encoding

The present invention relates to methods and apparatus for processing signals to remove redundant information thereby making the signals more suitable for transfer through a limited-bandwidth medium. The present invention specifically relates to methods and apparatus useful in video compression systems. Typically, the system determines differences between the current input signals and the previous input signals using mean-square difference signals. These mean-square signals are processed and compared with one or more thresholds for determining one of several modes of operation. After processing in some mode, the processed signals are in the form of digital numbers and these digital numbers are coded, using ordered redundancy coding, and transmitted to a receiver.

Coding system for reducing redundancy

A lossless image compression encoder/decoder system having a context determination circuit and a code table generator. The image compressor uses the context of a pixel to be encoded to predict the value of the pixel and determines a prediction error. The image compressor contains a context quantizer that quantizes the context of pixels. The image compressor counts the error values for each quantized context and uses these counts to generate context-specific coding tables for each quantized context. As it encodes a particular pixel, the encoder looks up the prediction error in the context-specific coding table for the context of the pixel and encodes that value. To decompress an image, the decompressor determines and quantizes the context of each pixel being decoded. The decompressor uses the same pixels as the compressor to determine the context. The decompressor retrieves from the context-specific coding table the error value corresponding to the coded pixel. The decompressor uses a predictor to predict the value of the pixel based on the context and adds the error value to determine the actual value of the pixel. In one embodiment the image compressor uses an alphabet extension, embedded in its context model, in specific low gradient contexts to reduce the redundancy of the encoding. Other systems and methods are disclosed.

System and method for lossless image compression

A data compression system for use in processing diagnostic image data which uses a predictor to predict future data. The actual data is subtracted from the predicted value to obtain data related difference values. The difference values are coded by coding the most prevalent difference by a code other than the least bit code but further coding the most prevalent number by string length coding, with the most common being the coded with a least bit code, and also coding the next most common difference with a least bit code and the subsequent most prevalent differences with sequential least bit codes to provide compression ratios of over 3:1. A procedure for finding the best predictor in noisy data is provided.

Data compression system

A ROM (200) includes a single dictionary of variable length codewords wherein Huffman codewords are assigned all members of the dictionary set, including one key codeword (246, 248) being assigned as a prefix codeword segment for a relatively large subgroup of the set, based on the combined probability (Pp) of occurrence of the subgroup as compared to the individual probabilities (P3, P4) of occurrences of the remaining members of the dictionary set. The key codeword (246, 248) is an indication of a departure from straightforward Huffman coding, to prepare an alternative coding scheme for developing a longer codeword which uses the key codeword as a prefix portion of that longer codeword. A unique suffix codeword segment follows the key codeword prefix for particularly identifying each member of the subgroup. The combined probability (Pp) of occurrence of a member of the subgroup is higher than the probability of occurrence of codewords (P3, P4) of shorter length, but the individual probabilities are significantly lower. The subgroup members can be assigned codeword lengths significantly shorter than codewords that would be assigned in straightforward Huffman coding.

Modified statistical coding of digital signals

A series of words each representing one of at least M (M≧3) different values is encoded by grouping the words into alternate runs of (1) a first, frequently occurring value, and (2) all other values. A coded representation of each run length as well as a representation of the non-frequent values which make up every other run are then combined in a predetermined sequence. Different code tables may be used to generate code words for each type of information.

Technique for encoding multi-level signals

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Technique for encoding multi-level signals