An evaluation method for print mottle using wavelet denoising and image grey level intensity gradient

Guodong Liu*, Meiyun Zhang, Qian Wang, Yongchang Chen, Xiaolin Lin, Patrick Gane

*Corresponding author for this work

    Research output: Contribution to journalArticleScientificpeer-review


    Print mottle is observed as an unevenness of printed tone across an image area. There are many causes of mottle on typical print media, i.e. printing and writing papers, packaging and board, as well as foils and polymer surfaces amongst others, in both applications of traditional printing techniques, such as offset and flexography as well as digital methods, including inkjet and electrophotography. Causes range from inhomo-geneous surface chemistry and absorption characteristics to instability factors on the printing press. Since the phenomenon is both physical and aesthetical, providing an evaluation for comparison purposes is challenging, frequently requiring panels of observers to provide a visual ranking. A new evaluation method is proposed using wavelet denoising and grey level gradient analysis of the print image. The index of print mottle is built on the bases of the average of grey level gradient and its distribution standard deviation. The method was tested for print mottle evaluation on paper in specific situations under different image basis functions and decomposition level. The results show that the method is in good agreement with visual assessment, and is also less time consuming both in the process and in statistical analysis, with correlation coefficient (r2) of at least 0.79 and as high as 0.88 with every function basis (level 2 or 3).

    Original languageEnglish
    Pages (from-to)280-285
    Number of pages6
    JournalNordic Pulp and Paper Research Journal
    Issue number2
    Publication statusPublished - 2014
    MoE publication typeA1 Journal article-refereed


    • Base function
    • Decomposition level
    • Discrete wavelet transform
    • Grey level gradient
    • Print mottle

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