The photograph is the only picture that can truly convey information, even if it is technically faulty and the object can barely be identified. A painting of a murder is of no interest whatever; but a photograph of a murder fascinates everyone.

To talk about paintings is not only difficult but perhaps pointless too. You can only express in words what words are capable of expressing-- what language can communicate. Painting has nothing to do with that.

A work of art is itself an object, first of all, and so manipulation is unavoidable: it's a prerequisite. But I needed the greater objectivity of the photograph in order to correct my own way of seeing: for instance, if I draw an object from nature, I start to stylize and to change it in accordance with my personal vision and my training. But if I paint from a photograph, I can forget all the criteria that I get from these sources. I can paint against my will, as it were. And that, to me, felt like an enrichment.

It can be a work by Mondrian, a piece of music by Schönberg or Mozart, a painting by Leonardo, Barnett Newman or also Jackson Pollock. That's beautiful to me. But also nature. A person can be beautiful as well. And beauty is also defined as 'untouched'. Indeed, that's an ideal: that we humans are untouched and therefore beautiful.

Well, the beginning is actually quite easy, because I can still be quite free about the way I handle things - colours, shapes. And so a picture emerges that may look quite good for a while, so airy and colourful and new. But that will only last for a day at most, at which point it starts to look cheap and fake. And then the real work begins - changing, eradicating, starting again, and so on, until it's done.

Photography has almost no reality; it is almost a hundred per cent picture. And painting always has reality: you can touch the paint; it has presence; but it always yields a picture - no matter whether good or bad. That's all the theory. It's no good. I once took some small photographs and then smeared them with paint. That partly resolved the problem, and it's really good - better than anything I could ever say on the subject.

The first colour charts were unsystematic. They were based directly on commercial colour samples. They were still related to Pop Art. In the canvases that followed, the colours were chosen arbitrarily and drawn by chance. Then, 180 tones were mixed according to a given system and drawn by chance to make four variations of 180 tones. But after that the number 180 seemed too arbitrary to me, so I developed a system based on a number of rigorously defined tones and proportions.