This section of ISO/IEC 23002 specifies the requirements for conformance in establishing an accurate integer-output IDCT implementation. It outlines the necessity for decoders to implement an 8×8 IDCT with integer output for generating sample differences with a specified range, specifically from -2B to (2B)-1 for a certain number of bits B, where B is greater than or equal to 8. This part aims to establish sufficient accuracy in such an integer-output IDCT implementation and serves as a reference for partial or complete requirements for IDCT accuracy in compliance with other standards that require IDCT use.
The accuracy requirements outlined in this section are essentially identical to those previously specified in [7], Annex A of [1], and Annex A of [5]. These specifications have been included herein to resolve references to [7] in MPEG standards following its withdrawal and to enhance clarity for specifying IDCT accuracy requirements.
Additionally, this part of ISO/IEC 23002 previously specified an additional requirement on intra refresh frequency for encoded-bitstreams. It established a requirement that each macroblock be intra-coded at least once within each series of 132 times it is coded in a predicted picture without an intervening intra picture. This additional requirement was not included in this section of ISO/IEC 23002, aiming to limit its scope to the domain of decoder conformance specification.
Some flexibility regarding modification of the specified accuracy requirements is allowed within this part of ISO/IEC 23002. The additional accuracy requirements that may be triggered by referencing specifications are detailed in Annexes A and B.
