Thanks for a good tip Olihar! I have tried the HD View export, but it crashed due to not enough ram. I'll try the zoomify export another time.
Klaus, the picture was to large for tiff format. But I used Giga Tiler to split the image in smaller .tiff images and used kmakemultires to stich the pictures back together. This procedure worked very well (Giga Tiler accepts .psb files as input)