ANSI AIIM TR33-1998 pdf download Selecting an Appropriate Image Compression Method to Match User Requirements
3.1.8 Transcoding: Conversion of an image from one specific compression method to another, different cornpression method.
3.2 Compression definitions The following terns provide compression definitions.
3.2.1 Quantization (uniform): The procedure by which a range of signal values is mapped to a single value.
3.2.2 Adaptive binary anthmetic encoder: An entropy encoding pmcedure that codes by means of a recunive subdivision of the probability of the sequence of symbols coded up to that point.
3.23 Component: Any of the two-dimensional arrays that comprise an image.
3.2.4 Compressed image data: A coded representation of an image that is intended to be smaller than the original representation of the image.
3.2.5 Controlled quality (lossy): A desuiptive temi for certain encoding and decoding processes that are not lossless. Controlled quai¡ compression allows for varying quality levels and thereby varying compression ratios. The compression ratio achieved is a fundion of the quality level chosen and the image complexity.
3.26 Decoding process: A process that takes as its input compressed image data and outputs a repmsentaiion of the original image.
3.2.7 Encoding process: A process that takes as its input an image and outputs compressed image data.
3.2.8 Entropy &coder. A lossless procedure that recovers the sequence of symbols from the sequence of bits produced by the entropy encoder.
3.2.9 Entropy encoding: A lossless procedure that conveils a sequence of input symbols into a sequence of bits such that the average number of bits per symbol approaches the entropy of the input symbols.
3.2.10 Hierarchical: A mode of operation for coding an image in which the first frame for a given component is followed by frames that code the differences between the source data and the wn stn i d ed data from the previous frame for that component. Resolution changes are allowed between frames.
3.2.11 Huffman table: The set of variables length codes required in a Huffman encoder and Huffman decoder.
3.2.12 Interchange format: The representation of compressed image data for exchange between application environments.
3.2.13 Interleaved: The dedptive tem applied to the repetitive multiplexing of small groups of data units from each component in a scan in a specific order.
3.2.14 JFIF (JPEG File Interchange Format): A minimal file format that enables JPEG bit-streams to be exchanged between a wide variety of platfoms and applications.
3.2.15 Modal: A term desaibing the value distribution charaderistics of components of an image. A modal image tends to have relatively large numbers of pixels grouped near the ?modes? or peaks in the distribution.
3.2.16 Progressive (coding): A DCT-based or hierarchical process defined in the JPEG or JBIG dandard in which each successive scan typically improves the quality of the reconstnicted image.
3.2.17 Quantization table: The set of 64 scalar quantization values used to quantize the DCT coefficients.
3.218 Run (length): Number of consecutive symbols of the same value.
3.2.19 Sample: One element in the two-dimensional array which comprises a component. 3.2.20 Scan: A single pass through the data for one or more of the components in an image.
3.2.21 Sequential (coding): One of the lossless or DCT-based coding processes defined in the JPEG standard in which each component of the image is encoded within a single scan.