How to change the colours of a bitmap that is loaded into a TImage

Problem/Question/Abstract:

How do I change the colors of a bitmap that is loaded into a TImage object? I have bitmaps that are displayed with a white background. I want to change all of the white pixels to black and all of the black pixels to white.

Answer:

Go over the picture with scanlines or whatever:

{ ... }
for x := 0 to width - 1 do
  for y := 0 to height - 1 do
  begin
    tc := img.canvas.pixels[x, y];
    if tc = clBlack then
      img.canvas.pixels[x, y] := clWhite;
    if tc = clWhite then
      img.canvas.pixels[x, y] := clBlack;
  end;