Application of wavelet de-noising in measurements of the printed line properties

In order to realize measurement for digitally printed line's attributes in accordance with the international standard ISO13660, wavelet de-noising technique is used in pre-processing the CCD digital image with high resolution of hardcopy line prints. First, the line attributes and their measurement indexes are presented. Then, Symltes (SymN) and Coiflets (CoifN) wavelets with hard threshold method are chosen based on theories and experiments. Further, dividing the image signals into two sections, signals of the line itself and the background, and analyzing their de-noising effects with different indexes, the proper wavelet parameters, which are order N in the wavelet functions and decomposition levels, are determined for a high resolution image of a line printed on a ink-jet printer. Experimental results indicate that the most properly parameter N and decomposition levels are 5 and 3 or 4 respectively for SymN, and for CoifN the results are 3 and 3 or 4 respectively. They can satisfy the de-noising requirements of a line CCD image with objectively keeping the line information and the same time smoothing the background information at the most extent.