Inverser un Bitmap

function InvertBmp(SourceBmp:Tbitmap): TBitMap;
var
i,j :longint;
tmp : TBitMap;
Red, Green, Blue: Byte;
PixelColor: Longint;
begin
tmp := TBitmap.Create;
tmp.width := SourceBmp.width;
tmp.height := SourceBmp.height;
for i := 0 to SourceBmp.width-1 do
begin
for j := 0 to SourceBmp.height-1 do
begin
PixelColor := ColorToRGB(SourceBmp.Canvas.Pixels[i,j]);
Red := PixelColor;
Green := PixelColor shr 8;
Blue := PixelColor shr 16;
red := 255-red;
green := 255-green;
blue := 255-blue;
tmp.canvas.pixels[i,j] := (red shl 8+green) shl 8+blue;
end;
end;
Result := tmp;
end;