An fast implemented,cheap way with many options would be the usage of TGIFImage
uses
gifimg;
Procedure ReduceTo8Bit(var bmp:TBitmap; ColorReduction: TColorReduction; DitherMode: TDitherMode);
var
GI:TGifImage;
begin
GI:=TGifImage.Create;
try
GI.DitherMode := DitherMode;
GI.ColorReduction := ColorReduction;
GI.Assign(bmp);
bmp.Assign(GI.Bitmap);
finally
GI.Free;
end;
end;
TEST
procedure TForm3.Button2Click(Sender: TObject);
var
bmp:TBitmap;
begin
bmp:=TBitmap.Create;
try
bmp.LoadFromFile('C:\bilder\bummi.bmp');
ReduceTo8Bit(bmp,rmQuantizeWindows,dmSierra);
bmp.SaveToFile('C:\bilder\bummi_8bit.bmp');
finally
bmp.Free;
end;
end;
a easier way will be using ReduceColors with rmQuantize from gifimg, if bits per pixel have to be set
// BytesPerPixel integer with range of Range 3 - 8
DestBMP := ReduceColors(SourceBMP,rmQuantize,dmNearest,BytesPerPixel,0);