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.

To me, grey is the welcome and only possible equivalent for indifference, noncommitment, absence of opinion, absence of shape. But grey, like formlessness and the rest, can be real only as an idea, and so all I can do is create a colour nuance that means grey but is not it. The painting is then a mixture of grey as a fiction and grey as a visible, designated area of colour.

The photograph is the most perfect picture. It does not change; it is absolute, and therefore autonomous, unconditional, devoid of style. Both in its way of informing, and in what it informs of, it is my source.

I first came up with the idea for the colour-chart pictures back in 1966, and my preoccupation with the topic culminated in 1974 with a painting that consisted of 4,096 colour fields. Initially I was attracted by the typical Pop Art aestheticism of using standard colour-sample cards; I preferred the unartistic, tasteful and secular illustration of the different tones to the paintings of Albers, Bill, Calderara, Lohse, etc.

It was not possible for us to produce the same optimism and the same kind of humour or irony. Actually, it was not irony. Lichtenstein is not ironic but he does have a special kind of humour. That's how I could describe it: humour and optimism. For Polke and me, everything was more fragmented. But how it was broken up is hard to describe.

If, while I'm painting, I distort or destroy a motif, it is not a planned or conscious act, but rather it has a different justification: I see the motif, the way I painted it, is somehow ugly or unbearable. Then I try to follow my feelings and make it attractive. And that means a process of painting, changing or destroying - for however long it takes - until I think it has improved. And I don't demand an explanation from myself as to why this is so.

I find the Romantic period extraordinarily interesting. My landscapes have connections with Romanticism: at times I feel a real desire for, an attraction to, this period, and some of my pictures are a homage to Caspar David Friedrich.