Psychophysical tests for visual-numerical correlation of whiteness formulas, TAPPI JOURNAL May 2016

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ABSTRACT: Measures of whiteness are important to the paper industry. Such measures must have good correlations with visual observations. In this study, psychophysical tests were conducted to determine if a visual correlation could be found between the International Commission on Illumination (CIE) whiteness formula and a formula previously derived by our group. The lightness value of the substrate has a significant effect on the perception of whiteness, so observer trials were carried out at approximately the same lightness levels. Perceptions of whiteness and their changes with different light sources were studied. Psychophysical tests were conducted using D₅₀ and D₆₅ light sources for visual correlations, under controlled viewing conditions at a 2° field angle. The psychophysical results were then compared with the two formulas. Considering available light sources for observer experiments and the standards used by the graphic arts industry, along with the effect of optical brightening agents on whiteness perception, recommendations for use of a different light source by the paper industry are provided.

Application: The Fleming-Aksoy whiteness formula overcomes limitations of the current CIE whiteness formula by showing better visual-numerical correlation and helps in determining optimum whiteness on bluer tone.