Converts any indexed format to any grayscale format.

procedure IndexToGray(NumPixels: LongInt; 
                      Src: PByte; 
                      Dst: PByte; 
                      SrcInfo: PImageFormatInfo; 
                      DstInfo: PImageFormatInfo; 
                      SrcPal: PPalette32);

ImagingFormats (at line 297)