Converts any grayscale format to any indexed format.

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

ImagingFormats (at line 274)