https://www.temlib.org/AtariForumWiki/index.php?action=history&feed=atom&title=PhotoChrome_file_format 2026-05-13T18:38:09Z Revision history for this page on the wiki MediaWiki 1.39.2 https://www.temlib.org/AtariForumWiki/index.php?title=PhotoChrome_file_format&diff=16071&oldid=prev 2017-01-03T00:03:55Z

<p>Created page with &quot;&lt;pre&gt; PhotoChrome *.PCS (low resolution only) 1 word 0x0140 (hex) x-resolution (always 320) 1 word 0x00C8 (hex) y-resolution (always 200) 1 byte 0...&quot;</p> <p><b>New page</b></p><div>&lt;pre&gt;<br /> PhotoChrome *.PCS (low resolution only)<br /> <br /> 1 word 0x0140 (hex) x-resolution (always 320)<br /> 1 word 0x00C8 (hex) y-resolution (always 200)<br /> 1 byte 00 = single screen mode<br /> nonzero value's = alternating screen mode,<br /> bit 0 (0x01) not set: second screen data is xor'ed with first screen<br /> bit 1 (0x02) not set: second color palette is xor'ed with first<br /> 1 byte bit 0 (0x01) set: 50 Hz mode, when not set 60 Hz mode<br /> ?? bytes compressed screen data<br /> ?? bytes compressed palette<br /> ?? bytes compressed second screen data (in case of alternating screens)<br /> ?? bytes compressed second palette<br /> -------------<br /> &gt; 18 bytes total<br /> <br /> Screen compression scheme:<br /> 1 word total number of control bytes that follow<br /> 1 control byte x<br /> x &lt; 0 : copy -x literal bytes (1 - 128)<br /> x = 0 : next word specifies the number of times the following byte <br /> has to be copied (0-65535)<br /> x = 1 : next word specifies the number of bytes to be copied (0-65535)<br /> x &gt; 1 : repeat the next byte x times (2-127)<br /> <br /> The 4 bitplanes are separated, first 8000 bytes of the first bitplane, then 8000 bytes <br /> for the second, 8000 bytes for the third and 8000 bytes for the fourth; a total of 32000 bytes.<br /> <br /> Palette compression scheme:<br /> the palette compression scheme is the same as the screen compression but it works with <br /> 16 bit words<br /> 1 word total number of control bytes that follow<br /> 1 control byte x<br /> x &lt; 0 : copy -x literal words (1 - 128)<br /> x = 0 : next word specifies the number of times the following word <br /> has to be copied (0-65535)<br /> x = 1 : next word specifies the number of words to be copied (0-65535)<br /> x &gt; 1 : repeat the next word x times (2-127)<br /> <br /> In total 9616 palette entries are stored. 200 scanlines with 3 palettes<br /> (48 colors) each, plus one final palette (16 colors). PhotoChrome files<br /> with a few extra entries have been found. The first scanline usually<br /> contains no data.<br /> <br /> /*<br /> * Given an x-coordinate and a color index, returns the corresponding<br /> * Photochrome palette index.<br /> *<br /> * by Hans Wessels; placed in the public domain January, 2008.<br /> */<br /> int find_pcs_index(int x, int c)<br /> {<br /> int x1=4*c;<br /> int index = c;<br /> if(x&gt;=x1)<br /> {<br /> index+=16;<br /> }<br /> if((x&gt;=(x1+64+12)) &amp;&amp; (c&lt;14))<br /> {<br /> index+=16;<br /> }<br /> if((x&gt;=(132+16)) &amp;&amp; (c==14))<br /> {<br /> index+=16;<br /> }<br /> if((x&gt;=(132+20)) &amp;&amp; (c==15))<br /> {<br /> index+=16;<br /> }<br /> x1=10*c;<br /> if((c&amp;1)==1)<br /> {<br /> x1-=6;<br /> }<br /> if((x&gt;=(176+x1)) &amp;&amp; (c&lt;14))<br /> {<br /> index+=16;<br /> }<br /> return index;<br /> }<br /> &lt;/pre&gt;<br /> Back to [[ST Picture Formats]]</div>

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