Think differently: There is no other way by which we see the picture than to look at it as a whole in our first view. We do not see each column of the B separately. They may be separated but only after our first glance as a whole and a following reflective thought. The imagination of the "fact" that each column in B is indeed brighter than as seen is possible only after we have kept in mind the picture as a whole. That is, it is NOT true that each column of B composes the whole picture.
We easily say, however, this as "illusion", something IS wrong. We want to see the atoms of the whole in order to understand the whole, and that is why we understand our reality through the other way round. However, we cannot know whether the atoms have ever existed in the world as fundamentally distinguished from its surroundings. We only grab the world as a whole FIRST. The trait of focusing on each atom is due to human's humble function of sensing the world, that its consciousness can embody at a time only a bit of its environment. "Human is atomist," philosopher Ian Hacking notes.