An evaluation method for print mottle using two-dimensional discrete wavelet analysis

Studying one of the most detrimental problems of print quality, print mottle, an evaluation method is proposed using two-dimensional discrete wavelet analysis, in which the index of print mottle is based on the sum of the detail energy of the digital image. The two important factors in the approach are the base function and decomposition level in the analysis process. The method was tested on papers with different structures, including offset paper, ink-jet paper, newsprint and coated paper and the evaluated indices compared with visual perception results. The result shows that the method proposed is reasonably effective in assessing print mottle; correlation with visual evaluation is at least 0.78 and in some cases as high as 0.84. The approach was best for offset paper and worst for coated paper.