C# faster way to compare pixels between two images and only write out the differences
===

Just doing a pixel-by-pixel comparison of two images that are very similar (one is an edited version of another) and writing out the differences to a new file.

    for (int y = 0; y < height; y++)
    {
        for (int x = 0; x < width; x++)
        {
            pix1 = src.GetPixel(x, y);
            pix2 = comp.GetPixel(x, y);
            if (pix1 != pix2)
            {
                dest.SetPixel(x, y, pix1);
            }
        }
    }

`src` and `comp` are the two images to compare and `dest` is just a new image.
It takes a fairly long time.

What's a faster way to do this?  
Maybe it's not necessary to actually get the pixel in order to compare it?