﻿ Whiteness - EN

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# Whiteness

Whiteness is a property important in many industries. Producers of white products decided that it would be easier to deal with whiteness as a single number index rather than three color scale parameters. As a result, various whiteness indices were developed. In order for a whiteness index to be valid, it must be used on the type of materials for which it was intended. When items are being compared using a whiteness index, they must be similar in gloss, texture, translucency, and other physical attributes. They must also be very near white. Whiteness values assigned to colored items are meaningless.

A perfect white is a Perfect Reflecting Diffuser (PRD), which has a value of 100. Pressed magnesium oxide (MgO) and pressed barium sulfate (BaSO4) are high-reflectance materials that closely approximate a PRD. Various whiteness indices exist and are used for numerous applications.

The whiteness index of the CIE is described in CIE Publication 15.2 (1986), pages 36-38.

## Whiteness index calculation

The whiteness index WI is calculated from the following equations:

WI = Y + 800 (xn - x) + 1700 (yn - y)

This equation is used for 2 degree standard observer and 10 degree standard observer.

where

WI is the whiteness index, Y the tristimulus value and xn, yn the chromaticity coordinates.

WI increases the more white an object appears to be. It takes the value 100 for a perfect reflecting diffuser (PRD). The WI value also depends on tint as well as lightness, e.g. if WI increases with increasing blueness of the object. For details, please refer to the tinting index calculation.

## Tinting index calculation

The whiteness of an object does not only depend on the whiteness index, but also on the tint and lightness. The whiteness must be interpreted as relative distance from a defined white point. Thus a sample cannot be called white, if tint increases excessively. The combination of all parameters let a sample appear white with a certain white temperature. To set a quantitative limit on it, the CIE tinting index TI is used.

The tinting index is calculated from the following equations:

TI = 1000.0 * (xn - x) - 650.0 * (yn - y)

TI = 900.0 * (xn - x) - 650.0 * (yn - y)

where

The greenness increases as TI increases in positive value.

The redness increases as TI increases in negative value.

TI = 0 means achromatic color.