#pas
procedure Threshold(Bitmap: TBitmap; Value: Byte; Color1, Color2: TColor);
var x, y: Word;
    C1, C2: TRGB;
    Dest: pRGB;
begin
  Bitmap.PixelFormat := pf24Bit;
  C1 := ColorToRGB(Color1);
  C2 := ColorToRGB(Color2);
  for y := 0 to Bitmap.Height - 1 do
  begin
    Dest := Bitmap.ScanLine[y];
    for x := 0 to Bitmap.Width - 1 do
    begin
      if (Dest^.r + Dest^.g + Dest^.b) / 3 > Value then Dest^ := C1 else Dest^ := C2;
      Inc(Dest);
    end;
  end;
end;