set_color_conversion - Man Page

#include <allegro.h>

void set_color_conversion(int mode);

Specifies how to convert images between the various color depths when  reading graphics from external bitmap files or datafiles. The mode is a  bitmask specifying which types of conversion are allowed. If the  appropriate bit is set, data will be converted into the current pixel  format (selected by calling the set_color_depth() function), otherwise it  will be left in the same format as the disk file, leaving you to convert  it manually before the graphic can be displayed. The default mode is  total conversion, so that all images will be loaded in the appropriate format for the current video mode. Valid bit flags are:

   COLORCONV_NONE                // disable all format
                                 // conversions
   COLORCONV_8_TO_15             // expand 8-bit to 15-bit
   COLORCONV_8_TO_16             // expand 8-bit to 16-bit
   COLORCONV_8_TO_24             // expand 8-bit to 24-bit
   COLORCONV_8_TO_32             // expand 8-bit to 32-bit
   COLORCONV_15_TO_8             // reduce 15-bit to 8-bit
   COLORCONV_15_TO_16            // expand 15-bit to 16-bit
   COLORCONV_15_TO_24            // expand 15-bit to 24-bit
   COLORCONV_15_TO_32            // expand 15-bit to 32-bit
   COLORCONV_16_TO_8             // reduce 16-bit to 8-bit
   COLORCONV_16_TO_15            // reduce 16-bit to 15-bit
   COLORCONV_16_TO_24            // expand 16-bit to 24-bit
   COLORCONV_16_TO_32            // expand 16-bit to 32-bit
   COLORCONV_24_TO_8             // reduce 24-bit to 8-bit
   COLORCONV_24_TO_15            // reduce 24-bit to 15-bit
   COLORCONV_24_TO_16            // reduce 24-bit to 16-bit
   COLORCONV_24_TO_32            // expand 24-bit to 32-bit
   COLORCONV_32_TO_8             // reduce 32-bit RGB to 8-bit
   COLORCONV_32_TO_15            // reduce 32-bit RGB to 15-bit
   COLORCONV_32_TO_16            // reduce 32-bit RGB to 16-bit
   COLORCONV_32_TO_24            // reduce 32-bit RGB to 24-bit
   COLORCONV_32A_TO_8            // reduce 32-bit RGBA to 8-bit
   COLORCONV_32A_TO_15           // reduce 32-bit RGBA to 15-bit
   COLORCONV_32A_TO_16           // reduce 32-bit RGBA to 16-bit
   COLORCONV_32A_TO_24           // reduce 32-bit RGBA to 24-bit
   COLORCONV_DITHER_PAL          // dither when reducing to 8-bit
   COLORCONV_DITHER_HI           // dither when reducing to
                                 // hicolor
   COLORCONV_KEEP_TRANS          // keep original transparency

For convenience, the following macros can be used to select common  combinations of these flags:

   COLORCONV_EXPAND_256          // expand 256-color to hi/truecolor
   COLORCONV_REDUCE_TO_256       // reduce hi/truecolor to 256-color
   COLORCONV_EXPAND_15_TO_16     // expand 15-bit hicolor to 16-bit
   COLORCONV_REDUCE_16_TO_15     // reduce 16-bit hicolor to 15-bit
   COLORCONV_EXPAND_HI_TO_TRUE   // expand 15/16-bit to 24/32-bit
   COLORCONV_REDUCE_TRUE_TO_HI   // reduce 24/32-bit to 15/16-bit
   COLORCONV_24_EQUALS_32        // convert between 24- and 32-bit
   COLORCONV_TOTAL               // everything to current format
   COLORCONV_PARTIAL             // convert 15 <-> 16-bit and
                                 // 24 <-> 32-bit
   COLORCONV_MOST                // all but hi/truecolor <-> 256
   COLORCONV_DITHER              // dither during all color reductions
   COLORCONV_KEEP_ALPHA          // convert everything to current format
                                 // unless it would lose alpha information

If you enable the COLORCONV_DITHER flag, dithering will be performed  whenever truecolor graphics are converted into a hicolor or paletted  format, including by the blit() function, and any automatic conversions  that take place while reading graphics from disk. This can produce much  better looking results, but is obviously slower than a direct conversion.

If you intend using converted bitmaps with functions like masked_blit()  or draw_sprite(), you should specify the COLORCONV_KEEP_TRANS flag. It  will ensure that the masked areas in the bitmap before and after the  conversion stay exactly the same, by mapping transparent colors to each  other and adjusting colors which would be converted to the transparent  color otherwise. It affects every blit() operation between distinct pixel  formats and every automatic conversion.

set_color_depth(3), load_bitmap(3), load_datafile(3), fixup_datafile(3), makecol15_dither(3), get_color_conversion(3), exalpha(3), exblend(3), exdata(3), exexedat(3), exlights(3), exrotscl(3), exxfade(3)

blit(3), exalpha(3), exblend(3), exdata(3), exexedat(3), exlights(3), exrotscl(3), exxfade(3), fixup_datafile(3), get_color_conversion(3), load_bitmap(3), load_datafile(3), load_datafile_callback(3), load_datafile_object(3), makecol15_dither(3), set_color_depth(3).