Scanline lahm??

[turboPASCAL]

Delphi-Quellcode:

procedure MakeDarker(Bitmap: TBitmap; const dp: Byte = 10);
var
  PixelLine: PByteArray;
  x, y: integer;
begin
  if Bitmap.PixelFormat <> pf24Bit then
    Bitmap.PixelFormat := pf24Bit;

  for y := 0 to Bitmap.height - 1 do
  begin
    PixelLine := Bitmap.ScanLine[y];
    for x := 0 to (Bitmap.width * 3) - 1 do
       PixelLine^[x] := PixelLine^[x] - round(PixelLine^[x] / dp);
  end;
end;

Die tut's bei mir recht schnell.