The folding process is one of the most commonly used print finishing operations in graphical production. Therefore, surface damages on coated papers and paperboards, which are frequently appearing during this process, can have significant negative economic and environmental impacts. To reduce the adverse effects, fold crack resistance has become an active field of research. In the last decades, there were several computer-aided visual assessment methods introduced for fold-crack evaluation. These techniques were based on similar concepts of digital image analysis to quantitatively characterise the surface damage, but they had differences in utilisation as well as in the used image feature. In this study, fold crack distribution has been introduced as a new digital image feature for quality assessment. Fold crack distribution can be determined as a measure of crack scattering over the folding line. In this paper descriptive statistics, mean value, standard deviation and coefficient of variance have been used for qualitative characterisation of surface damage. The obtained results for mean value demonstrated increasing tendency by increasing the basis weight and had slightly lower value for samples in machine than cross direction. These results confirm the basic assumptions that on thicker substrates (i.e. on samples with higher basis weight) the cracks are larger, longer or grouped and that the folding process generates higher surface destruction is cross than machine direction. In the case of standard deviation, results suggest that in a case of varying mean values, crack distribution should be defined via coefficient of variation. Based on this analysis, the proposed approach to the calculation of crack distribution can serve as a new image characteristic for the qualitative measurement of the fold-crack resistance of coated papers.
Quality control of digital photos is evolving rapidly every day. Procedures and methods of measurement are changing. Cameras on mobile phones are currently in focus because they are largely replacing the cameras used so far. Based on the standards for the control of photos on mobile phones, in this paper one of the essential quality attributes was chosen to be tested, which is the sharpness of the photos. For the purposes of the experiment, five commercially available mobile phones with different rear camera characteristics were selected. Two standard test cards with different contrast ratios were used. The tests were carried out under appropriate laboratory conditions. Sharpness is analaziry via MTF50 value as measured in Imatest software. Based on the results, it is concluded that the contrast of the test chart affects the measured value, therefore it is important to strictly define the conditions of measurement and the used test card when analyzing this attribute.
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