Each of the four images has geometrical distortions similar to those you see
when you look through a magnifying glass. To combine the images of the four
different cameras into a single, accurate picture of the nebula, we need to map
and remove those distortions. Once we've done so, the four images fit together
nicely, giving us this single mosaic image of How It Sees, showing
light coming through the oxygen filter.
Now the picture is beginning to resemble its final self. But who wants those
ugly seams? Let's erase them.