var
 resultBmp : TBitmap;
 sourceBmp : TBitmap;
begin
 sourceBmp := TBitmap.Create;
 sourceBmp.LoadFromFile("c:\tmp.bmp");
 resultBmp := Create8bitFrom24bitBitmap(sourceBmp, 8);
 
 image1.Canvas.Draw(resultBmp, 0, 0);
end;