1. A sheet-surface analyser including: illuminating means for casting shadows on the sheet-surface; capturing means for capturing an image of the shadows; analysing means for analysing the captured shadow-image to thereby analyse the sheet-surface; and curving means for curving the sheet, wherein the illuminating means and the curving means are configured to enable the illuminating means to illuminate a curved part of the sheet-surface so that features of the sheet-surface cast shadows on the sheet-surface and the capturing means is configured to capture said shadow-image.