Converts any ARGB format to any indexed format.

procedure ChannelToIndex(NumPixels: LongInt; 
                         Src: PByte; 
                         Dst: PByte; 
                         SrcInfo: PImageFormatInfo; 
                         DstInfo: PImageFormatInfo; 
                         DstPal: PPalette32);

ImagingFormats (at line 261)