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Explain the purpose of the wc3_pal_lookup and the formula that was used to

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calculate it.

Originally committed as revision 18445 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Reimar Döffinger 2009-04-11 20:08:16 +00:00
parent f6a708f092
commit cdbe3798d2
1 changed files with 12 additions and 1 deletions
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13
libavformat/wc3movie.c
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@ -72,7 +72,18 @@ typedef struct Wc3DemuxContext {
} Wc3DemuxContext;
/* bizarre palette lookup table */
/**
* palette lookup table that does gamma correction
*
* can be calculated by this formula:
* for i between 0 and 252 inclusive:
* wc3_pal_lookup[i] = pow(i / 256.0, 0.8) * 256;
* values 253, 254 and 255 are all 0xFD
* calculating this at runtime should not cause any
* rounding issues, the maximum difference between
* the table values and the calculated doubles is
* about 0.497527
*/
static const unsigned char wc3_pal_lookup[] = {
0x00, 0x03, 0x05, 0x07, 0x09, 0x0B, 0x0D, 0x0E,
0x10, 0x12, 0x13, 0x15, 0x16, 0x18, 0x19, 0x1A,