https://temlib.org/AtariForumWiki2018/index.php?action=history&feed=atom&title=Spectrum_512_file_format 2026-10-19T01:58:35Z Revision history for this page on the wiki MediaWiki 1.30.0 https://temlib.org/AtariForumWiki2018/index.php?title=Spectrum_512_file_format&diff=9671&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_file_format&diff=9670&oldid=prev 2017-01-02T23:50:58Z

<p>New page</p> <p><b>New page</b></p><div>&lt;pre&gt;<br /> Spectrum 512 *.SPU<br /> <br /> 80 words first scan line of picture (unused) -- should be zeroes<br /> 15920 words picture data (screen memory) for scan lines 1 through 199<br /> 9552 words 3 palettes for each scan line (the top scan line is<br /> not included because Spectrum 512 can't display it)<br /> -----------<br /> 51104 bytes total<br /> <br /> Note that the Spectrum 512 mode's three palette changes per scan<br /> line allow more colors on the screen than normally possible, but a<br /> tremendous amount of CPU time is required to maintain the image.<br /> <br /> The Spectrum format specifies a palette of 48 colors for each scan line.<br /> To decode a Spectrum picture, one must be know which of these 48 colors<br /> are in effect for a given horizontal pixel position.<br /> <br /> Given an x-coordinate (from 0 to 319) and a color index (from 0 to 15),<br /> the following C function will return the proper index into the Spectrum<br /> palette (from 0 to 47):<br /> <br /> /*<br /> * Given an x-coordinate and a color index, returns the corresponding<br /> * Spectrum palette index.<br /> *<br /> * by Steve Belczyk; placed in the public domain December, 1990.<br /> */<br /> int <br /> FindIndex(x, c)<br /> int x, c;<br /> {<br /> int x1;<br /> <br /> x1 = 10 * c;<br /> <br /> if (1 &amp; c) /* If c is odd */<br /> x1 = x1 - 5;<br /> else /* If c is even */<br /> x1 = x1 + 1;<br /> <br /> if (x &gt;= x1 &amp;&amp; x &lt; x1 + 160) <br /> c = c + 16;<br /> else if (x &gt;= x1 + 160) <br /> c = c + 32;<br /> <br /> return c;<br /> }<br /> &lt;/pre&gt;<br /> Back to [[ST Picture Formats]]</div>

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