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Defect Report Number: 8632-4/009
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Submitter: Henderson
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Addressed to: JTC1/SC 24/WG 6 Rapporteur Group on ISO/IEC 8632, CGM
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WG secretariat: NNI
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Date Circulated by WG secretariat: 1 July 1995
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Deadline on response from editor: 1 October 1995
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Defect Report concerning IS 8632:1992 Computer Graphics: Metafile for the storage and transfer of picture description information (CGM) Part 4, Clear text encoding.
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Qualifier (e.g. error, omission, clarification required): Clarification.
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References in document (e.g. page, clause, figure and/or table numbers):Part 1, clause 5.6.29, TILE, and the encodings sections for TILE (especially Part 4, Clear Text, clause 5.3.6).
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Nature of defect (complete, concise explanation of the perceived problem):
The content of the TILE element is inherently binary, regardless of the encoding. If the compression type is "bitmap" (uncompressed), then the BS parameter is the concatenation of cell colour specifiers whose size is specified by the Cell Colour Precision. In the Binary and Character encodings, this is measured in bits. In Clear Text, it is a maximum value. In the latter case, what is intended if the value is not a power of 2, e.g., supposed it was 12? What is intended? Should the next larger bit width be used for encoding the bit stream, e.g., 4 bits in this case? It does not appear possible to deterministically decode the BS parameter if such an interpretation is not taken.
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Solution proposed by the submitter (optional):
Clarify Part 4, clause 5.3.6, that the next-largest bit width is used to encode the BS parameter if Cell Colour Precision is not a power of 2.
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Editor's response (any material proposed for processing as a technical corrigendum to, an amendment to, or a commentary on the International Standard or DIS final text is attached separately to this completed report):
Add at end of 5.3.6: "If the cell colour precision indicated by the cell colour precision parameter is 2**N -1, for some integer N greater than 0, then N bits are used to encode the BS parameter. Otherwise the next-largest bit width, N+1, such that 2**N-1<cell colour precision<2**(N+1)-1, is used to encode the BS parameter."
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