Evaluating the contrast of planar periodic patterns on paper

Certain paper products contain functional or' decorative periodic patterns. Such patterns can be e.g. the 3 D structure variations in tissue paper or the decorative sfructure 'n tobacco paper. At present, the contrast of such patterns is not measured online and thus the uniformity of the end-products may vary.Trus paper Introduces two contrast estimation methods based on Fourier and histogram analysis. The performance of the estimation methods was evaluated with the reference results made by the human panel. It was noticed that both methods estimate the contrast rather reliably. However, if the wavelength of the pattern was close to the size of the image, the Fourier method was not working appropriately. The image data available in this work was collected online at the tobacco and tissue paper machines. The tobacco paper was measured with light transmittance imaging system and the tissue paper was measured with photometric stereo imaging system that estimates the 3 D surface of the paper. It was noticed that the present imaging systems can be utilized as sUch in the estimation of contrast.