The intensity of the background visual effect of crispening depending on background lightness

U radu su prezentirani rezultati istraživanja pozadinskog vizualnog efekta nabiranja u ovisnosti o svjetlini pozadine. Provedeno je istraživanje na grafičkim reprodukcijama sa specifično konstruiranim rješenjima u kojima se javlja spomenuti efekt. Reprodukcije su dizajnirane putem varijacija 4 različite pozadine svjetlina 25%, 50%, 75% i 100% RTV (sekundarni stimulus), na kojima se nalaze unutrašnji pravokutnici svjetlina 45%, 50% i 55% RTV (primarni stimulusi). Vizualni eksperiment proveden je upotrebom tehnike simultanog binokularnog usuglašavanja sa 10 ispitanika. ANOVOM s ponovljenim mjerenjima utvrđene su statističke razlike među aritmetičkim sredinama odstupanja u svjetlinama za 4 varijacije pozadine i to kod sva 3 primarna stimulusa. Daljnjom post-hoc analizom po Fisheru identificirane su grupe koje se međusobno razlikuju. Dobiveni rezultati ukazuju na pravilnosti kojima se podvrgava efekt nabiranja u izabranom grafičkom mediju. Istraživanje je provedeno s ciljem standardizacije tiskarskog procesa prilikom pojavnosti efekta nabiranja u realnim uvjetima grafičke proizvodnje.The paper presents the results of a research of the background visual effect of crispening depending on background lightness. A research on graphic reproductions with specifically designed solutions that involve the mentioned effect was conducted. Reproductions were designed through the variations of four different types of background lightness of 25%, 50%, 75% and 100% RTV (secondary stimuli), on which there are internal rectangles of lightness of 45%, 50% and 55% RTV (primary stimuli). The visual experiment was carried out through the use of the technique of simultaneous binocular harmonization with 10 respondents. The ANOVA with repeated measures revealed statistical differences between the arithmetic means of variations in lightness for four variations of the background in all three primary stimuli. Further post-hoc analysis by Fisher identified the groups that mutually differ. The results indicate the regularities to which the effect of crispening is subjected in the selected graphic medium. The research was conducted with the aim of standardizing the printing process during the appearance of crispening effect in real conditions of graphic production

Grey scale, the 'crispening effect', and perceptual linearization

One way of optimizing a display is to maximize the number of distinguishable grey levels, which in turn is equivalent to perceptually linearizing the display. Perceptual linearization implies that equal steps in grey value evoke equal steps in brightness sensation. The key to perceptual linearization is hence to understand the relationship between screen luminance (differences) and perceived brightness (differences). We start with an overview of psychophysical laws on the brightness-luminance relationship. We present alternative models from the literature for describing this relationship. Existing models are compared with our human-performance data that were discussed in an earlier paper. We show that Whittle’s model provides a good fit to our experimental data, provided that some of the model parameters are allowed to depend on the surround luminance. An alternative model by Kingdom and Moulden, however, needs to be modified in order to accomplish agreement with experimental data