https://temlib.org/AtariForumWiki2018/index.php?action=history&feed=atom&title=Spectrum_512_Compressed_file_format 2026-10-19T01:30:53Z Revision history for this page on the wiki MediaWiki 1.30.0 https://temlib.org/AtariForumWiki2018/index.php?title=Spectrum_512_Compressed_file_format&diff=9657&oldid=prev 2018-06-03T23:13:49Z

<p>1 revision imported</p> <table class="diff diff-contentalign-left" data-mw="interface"> <tr style="vertical-align: top;" lang="en"> <td colspan="1" style="background-color: white; color:black; text-align: center;">← Older revision</td> <td colspan="1" style="background-color: white; color:black; text-align: center;">Revision as of 23:13, 3 June 2018</td> </tr><tr><td colspan="2" style="text-align: center;" lang="en"><div class="mw-diff-empty">(No difference)</div> </td></tr></table>

AtariWikiSysop https://temlib.org/AtariForumWiki2018/index.php?title=Spectrum_512_Compressed_file_format&diff=9656&oldid=prev 2017-01-02T23:54:10Z

<p>New page</p> <p><b>New page</b></p><div>&lt;pre&gt;<br /> Spectrum 512 (Compressed) *.SPC<br /> <br /> 1 word flag word [$5350 or &quot;SP&quot;]<br /> 1 word reserved for future use [always 0]<br /> 1 long length of data bit map<br /> 1 long length of color bit map<br /> &lt;= 32092 bytes compressed data bit map<br /> &lt;= 17910 bytes compressed color bit map<br /> --------------<br /> &lt;= 50014 bytes total<br /> <br /> Data compression:<br /> <br /> Compression is via a modified run length encoding (RLE) scheme,<br /> similar to DEGAS compressed and Tiny. The data map is stored as a<br /> sequence of records. Each record consists of a header byte followed by<br /> one or more data bytes. The meaning of the header byte is as follows:<br /> <br /> For a given header byte, x:<br /> <br /> 0 &lt;= x &lt;= 127 Use the next x + 1 bytes literally (no repetition)<br /> -128 &lt;= x &lt;= -1 Use the next byte -x + 2 times<br /> <br /> The data appears in the following order:<br /> <br /> 1. Picture data, bit plane 0, scan lines 1 - 199<br /> 2. Picture data, bit plane 1, scan lines 1 - 199<br /> 3. Picture data, bit plane 2, scan lines 1 - 199<br /> 4. Picture data, bit plane 3, scan lines 1 - 199<br /> <br /> Decompression of data ends when 31840 data bytes have been used.<br /> <br /> Color map compression:<br /> <br /> Each 16-word palette is compressed separately. There are three<br /> palettes for each scan line (597 total). The color map is stored as a<br /> sequence of records. Each record starts with a 1-word bit vector which<br /> specifies which of the 16 palette entries are included in the data<br /> following the bit vector (1 = included, 0 = not included). If a palette<br /> entry is not included, it is assumed to be zero (black). The least<br /> significant bit of the bit vector refers to palette entry zero, while the<br /> most significant bit refers to palette entry 15. Bit 15 must be zero,<br /> since Spectrum 512 does not use palette entry 15. Bit 0 should also be<br /> zero, since Spectrum 512 always makes the background color black.<br /> The words specifying the values for the palette entries indicated in<br /> the bit vector follow the bit vector itself, in order (0 - 15).<br /> <br /> NOTE: Regarding Spectrum pictures, Shamus McBride reports the following:<br /> <br /> &quot;... [The Picture Formats List] says bit 15 of the color map vector<br /> must be zero. I've encountered quite a few files where [bit 15] is <br /> set (with no associated palette entry)...&quot;<br /> &lt;/pre&gt;<br /> See also [[Spectrum 512 file format]]<br /> <br /> Back to [[ST Picture Formats]]</div>

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