[FFmpeg-cvslog] r18445 - trunk/libavformat/wc3movie.c

[reimar]

Author: reimar
Date: Sat Apr 11 22:08:16 2009
New Revision: 18445

Log:
Explain the purpose of the wc3_pal_lookup and the formula that was used to
calculate it.

Modified:
   trunk/libavformat/wc3movie.c

Modified: trunk/libavformat/wc3movie.c
==============================================================================
--- trunk/libavformat/wc3movie.c	Sat Apr 11 20:58:55 2009	(r18444)
+++ trunk/libavformat/wc3movie.c	Sat Apr 11 22:08:16 2009	(r18445)
@@ -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,