Whiteness

In colorimetry, whiteness is the degree to which a surface is white. An example of its use might be to quantitatively compare two pieces of paper which appear white viewed individually, but not when juxtaposed.

The International Commission on Illumination describes it in the following terms:

To promote uniformity of practice in the evaluation of whiteness of surface colors, it is recommended that the formulæ for whiteness, W2 or W10, and for tint, Tw,2 or Tw,10, given below, be used for comparisons of the whiteness of samples evaluated for CIE standard illuminant D65. The application of the formulae is restricted to samples that are called "white" commercially, that do not differ much in color and fluorescence, and that are measured on the same instrument at nearly the same time. Within these restrictions, the formulæ provide relative, but not absolute, evaluations of whiteness, that are adequate for commercial use, when employing measuring instruments having suitable modern and commercially available facilities.

— CIE Publication 15:2004

Calculation

${\displaystyle W_{10}=Y_{10}+800(x_{n,10}-x_{10})+1700(y_{n,10}-y_{10})}$

${\displaystyle T_{w,2}=1000(x_{n,2}-x_{2})-650(y_{n,2}-y_{2})}$

${\displaystyle T_{w,10}=900(x_{n,10}-x_{10})-650(y_{n,10}-y_{10})}$

where

Y is the Y tristimulus value (relative luminance),
(x,y) is the chromaticity coordinate in the CIE 1931 color space
(xn,yn) is the chromaticity coordinate of the perfect diffuser (reference white)
The numbers in the subscript indicate the observer: two for the CIE 1931 standard observer and ten for the CIE 1964 standard observer.

Notes
W increases with whiteness, reaching 100 for the perfect diffuser.
The tint is green for positive T and red for negative T.
Equal differences in W may not appear equally different.

methods
Since the degree of whiteness depends on various factors, such as the amount of light or the color of the illumination, the measurement conditions and the calculation methods must be precisely described. There is not the "whiteness per se", but only the "whiteness after ...". A common method in the paper industry is Berger's whiteness. This approach becomes understandable when one realizes that the variety of colors in the visual space is reduced to a measure. The whiteness loses value as soon as the color cast becomes too large. The whiteness of a red can no longer make sense.

Using different formulas, one obtains the whiteness from equipment data or color measurement, controversially noted as yellowness.

Whiteness to Berger
Whiteness to Hunter
Whiteness to Whole, Whiteness to Ganz / Griesser
Whiteness to Stensby
Whiteness to Stephanson
Whiteness to CIE
Yellow value according to DIN 6167
Whiteness according to ASTM E313, according to ASTM D9125
Brightness according to ISO 2470, here called brightness
Whiteness after Tappi 525 and R 457
Whiteness after pigeon
Yellowness to CIE
Yellowness according to ASTM (yellowness)
The L * value of the Lab color space is also suitable as a whiteness measure.
Preference should be given to using ISO whiteness, which is particularly useful for paper as a quality indicator. A good, white paper that has not lightened (copy paper) has a whiteness of about 160, according to Berger.

A conversion between the degrees of whiteness without knowledge of the spectrophotometric values is not always possible. The cause is that a color cast in some formulas goes unnoticed. However, metamerism prevents the numerical value of whiteness from unambiguously assigning it back to the spectral arrangement. It is not possible to "calculate out" the weighting of a shade when converting degrees of white.

application
The whiteness serves as a quality feature for the assessment of undyed (white) products in the paper industry. Of particular importance is the whiteness of coated papers. For white textiles it is usual as quality measure. To a lesser degree, the use of this measure in the plastics industry, here rather in the selection of fillers or binders.

The determination of the whiteness depends on the field of application and the intended objective by colorimetric, photometric or spectrophotometric measurement methods.

Objectives of the application
Whiteness is a standard test in paper production.
Sufficient whiteness for papers, which are used as substrate to achieve the sufficient contrast.
Recycled papers with gray tone, for instance because of an ineffective Deinkings, are printed worse readable than high-white papers after a chlorine bleach.
A high degree of whiteness is necessary in particular for conventional photo papers, so that the contrast between photosilver and background can be improved.
Coatings for art papers must be bright white, as the paper white is the eighth coloring component in addition to six bright colors and black.
The whiteness is used to measure the success of bleaching operations.
It is a means to characterize the effectiveness of detergents on textiles.
The degree of whiteness serves as a quality indicator for white interior paints, exterior paints, plasters and other colorants.
The whiteness is used to control the quality of fillers for the paper industry.
side effects
The whiteness is usually determined under standard light, which differs from natural daylight due to the lower proportion of short-wave UV radiation.

However, optically brightened textiles or paper absorb UV light due to fluorescence and emit visible light. Visually this (possibly) affects the whiteness of the whiteness, but with UV-free light this additional light would not be measurable. The whiteness gives only the uncoloured portion of a measured area in relation to an ideal white (density 0) or ideally black area (density 2). For optically brightened substrates so far two statements are necessary, which are to be measured on the one hand with and without UV excitation. This corresponds to the "perceived white" in sunny daylight and in UV-free artificial light.

An increase in whiteness in the washing of textiles can also be achieved by blueing.

A nuance in red or yellow is disturbed in white as a "metrologically" same blue cast, to a lesser extent as a green cast. Therefore, not only the dimensional number of the degree of whiteness and the method are to be reconciled with quality indicators, but also a color deviation. This permissible deviation can be determined as color temperature, verbal or colorimetric.

Source From Wikipedia