A lot of different things had to come together over the years, accumulated experiences of a general and personal nature, before the idea and the decision were developed and then carried out.

Everything has a reason, including the selection of the photos, which was not arbitrary but appropriate to the period, its highs and lows and my sense of them.

I believe I am looking for rightness. My work has so much to do with reality that I wanted to have a corresponding rightness. That excludes painting in imitation. In nature everything is always right: the structure is right, the proportions are good, the colours fit the forms. If you imitate that in painting, it becomes false.

Suddenly, I saw it in a new way, as a picture that offered me a new view, free of all the conventional criteria I had always associated with art. It had no style, no composition, no judgment. It freed me from personal experience. For the first time, there was nothing to it: it was pure picture. That's why I wanted to have it, to show it - not use it as a means to painting but use painting as a means to photography.

Grey. It makes no statement whatever; it evokes neither feelings nor associations: it is really neither visible nor invisible. Its inconspicuousness gives it the capacity to mediate, to make visible, in a positively illusionistic way, like a photograph. It has the capacity that no other colour has, to make 'nothing' visible.

But my motivation was more a matter of wanting to create order - to keep track of things. All those boxes full of photographs and sketches weigh you down, because they have something unfinished, incomplete, about them. So it's better to present the usable material in an orderly fashion and throw the other stuff away. That's how the Atlas came to be, and I exhibited it a few times.

Turning to the colour-classification methodology: The starting point are the four pure colours red, yellow, green and blue; their in-between shades and scales of brightness result in colour schemes containing 16, 64, 256 and 1,024 shades. More colours would be pointless because it wouldn't be possible to distinguish between them clearly.