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ISO/IEC 10918-1 : 1993(E)
5
Interchange format requirements
The interchange format is the coded representation of compressed image data for exchange between application
environments.
The interchange format requirements are that any compressed image data represented in interchange format shall comply
with the syntax and code assignments appropriate for the decoding process selected, as specified in Annex B.
Tests for whether compressed image data comply with these requirements are specified in Part 2 of this Specification.
6
Encoder requirements
An encoding process converts source image data to compressed image data. Each of Annexes F, G, H, and J specifies a
number of distinct encoding processes for its particular mode of operation.
An encoder is an embodiment of one (or more) of the encoding processes specified in Annexes F, G, H, or J. In order to
comply with this Specification, an encoder shall satisfy at least one of the following two requirements.
An encoder shall
a)
with appropriate accuracy, convert source image data to compressed image data which comply with the
interchange format syntax specified in Annex B for the encoding process(es) embodied by the encoder;
b)
with appropriate accuracy, convert source image data to compressed image data which comply with the
abbreviated format for compressed image data syntax specified in Annex B for the encoding process(es)
embodied by the encoder.
For each of the encoding processes specified in Annexes F, G, H, and J, the compliance tests for the above requirements
are specified in Part 2 of this Specification.
NOTE There is no requirement in this Specification that any encoder which embodies one of the encoding processes
specified in Annexes F, G, H, or J shall be able to operate for all ranges of the parameters which are allowed for that process. An
encoder is only required to meet the compliance tests specified in Part 2, and to generate the compressed data format according to
Annex B for those parameter values which it does use.
7
Decoder requirements
A decoding process converts compressed image data to reconstructed image data. Each of Annexes F, G, H, and J
specifies a number of distinct decoding processes for its particular mode of operation.
A decoder is an embodiment of one (or more) of the decoding processes specified in Annexes F, G, H, or J. In order to
comply with this Specification, a decoder shall satisfy all three of the following requirements.
A decoder shall
a)
with appropriate accuracy, convert to reconstructed image data any compressed image data with parameters
within the range supported by the application, and which comply with the interchange format syntax
specified in Annex B for the decoding process(es) embodied by the decoder;
b)
accept and properly store any table-specification data which comply with the abbreviated format for table-
specification data syntax specified in Annex B for the decoding process(es) embodied by the decoder;
c)
with appropriate accuracy, convert to reconstructed image data any compressed image data which comply
with the abbreviated format for compressed image data syntax specified in Annex B for the decoding
process(es) embodied by the decoder, provided that the table-specification data required for decoding the
compressed image data has previously been installed into the decoder.
Additionally, any DCT-based decoder, if it embodies any DCT-based decoding process other than baseline sequential,
shall also embody the baseline sequential decoding process.
For each of the decoding processes specified in Annexes F, G, H, and J, the compliance tests for the above requirements
are specified in Part 2 of this Specification.
CCITT Rec. T.81 (1992 E)
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