Some New Experiments on the Colorimetric Evaluation of Whiteness

Abstract

In order to confirm and extend earlier work on the colorimetric evaluation of whiteness, different series of white textiles, each of constant reflectance, varying from Y = 96 to Y = 70, are studied. A study of the Ciba-Geigy white scale is also included.Earlier predictions about the shape of the equi-whiteness surfaces in the x, y, Y colour space are confirmed and refined. As a result it is established that our original method used as such (using a diagram in the x, y chromaticity chart) or as adapted jbr numerical computation by Ganz, is applicable to nearly all white textiles, with or without FWAs. Only if shading dyes are used can the colour point trnnsgress the optimum whiteness point corresponding to the reflectance of the material. In such cases it is necessary to use equi-whiteness ellipses around the optimum point, whose position in the chromaticity diagram varies nearly linearly with reflectance. it is also found that catastrophe theory applies to whiteness perception in the vicinity of the optimum whiteness axis in colour space. This means that the whiteness of a given colour in this domain can have a high and a low value, according to circumstances.

Two Neutral White Illumination Loci Based on Unique White Rating and Degree of Chromatic Adaptation

“…Note that although observers also judged the color appearance of objects in the chromatic adaptation experiments, the derivation of the degree of adaptation effectively singled out (although there possibly was some impact of simultaneous contrast; Smet and others [2017b]) the illumination contribution to the whiteness perception of the stimuli. These two different modes of stimulus appearance can result in two different whiteness or neutrality perceptions through, for example, the enhanced whiteness perception associated with a slight purple or blue shift of object chromaticity [David and others 2013; Fairchild 2010; Katayama and others 2007;Vaeck 1979] or, as Grum and Patek [1965;p. 357] stated, It is evident that the apparent whiteness of a sample is dependent upon its chromaticness, i.e., a function of dominant wavelength and purity, and upon its luminous reflectance.…”

Whiteness evaluation: A review and new proposals

“…Saturation had already been taken into account namely by Friele for a long time, 5 but often evaluated by the excitation purity, 6,7 which is not easily computed.…”

“…This is what has been continuously applied for most of the old whiteness formulas and for that of the CIE, a principle established as a theorem by Ganz 15 and translated by the relation. (6)…”

Visual and instrumental evaluation of whiteness and yellowness

“…The decision would then have to be taken whether to prefer a white with a somewhat higher luminance factor, or one with lower chroma, or a third one with a different tint. According to Vaeck (1979): 'At any given level of illuminance and for all normal observers, the chromaticity corresponding to the highest whiteness perception is never identical with the achromatic colour. It is always to the blue or purple side of the achromatic point (achromatic being taken here in the colorimetric sense).…”