Objective colour evaluation and the visual threshold

Anica Hunjet

Abstract


The science of colour is concerned with developing theories and establishing facts about colour which help us understand the perception of colour and provide the means for objective colour specification. Scientific research in this FIELD must consider different factors that affect colour perception such as the observer’s experience and behaviour. Spectrophotometric colour measurement methods are based on the tristimulus values (X, Y and Z) and describe colour by three psychological attributes: chroma (C), hue (H) and lightness (L). These values are objective and are not affected by observer characteristics and their environment.

By using an instrumental, i.e. spectrophotometric method, a threshold is identified in order to predict the area in which the visual perception of colour, i.e. the psychological (subjective) experience matches the C* to L* ratio. The experiment is carried out using complementary colours - red and green, based on the opponent colour theory.

182 subjects aged 20-50 participated in the experiment in which objective spectrophotometric method is compared against the psychophysical, i.e. subjective perception of colour. Psychophysical methods, i.e. the method of constant stimuli and Stevens' magnitude estimation are used to measure the subjective perception of colour influenced by different backgrounds (white, grey and black).

Among the subjects aged 30 and over, higher inaccuracy is observed in rating the position of the sample for the parameter lightness (L). For the parameter chroma (C), all subjects, irrespective of their age, displayed uncertainty in rating the position of the sample.

Descriptive statistics and appropriate nonparametric tests (the Mann-Whitney U test, the Kruskal-Wallis test and the Median test) show significant differences in inaccurate visual perception of colour depending on the surround colour, in particular for the parameter lightness (L) and for the red hue.

 


Keywords*


spectrophotometric measurements, red and green hues, visual perception, descriptive statistics, psychological colour attributes

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