TABLE OF CONTENTS The accurate measurement of color is a difficult task. While cameras and image scanners record color information, they are not suitable for the most accurate color measurements. For the accurate measurement of color, the instrument must have carefully controlled sensors (filters and detectors) and optical geometry. If the color of reflective material is to be measured, the illumination must be precisely known and matched with the sensors. There are physical problems with the color media that further complicate the task. Properties such as specular reflectance and translucence should be taken into account. These properties will be discussed in the follow sections.
If only the tristimulus values or some derivative of them, such as L* a* b* values, are desired, a colorimeter can be used. This device uses filters to match the vector space defined by the eye. Thus, a measurement is limited to one set of viewing conditions. The colorimeter need measure only the quantities that can be transformed into tristimulus values. The minimal system consists of three filters and three detectors or changeable filters and a single detector. These devices are much less expensive than the devices designed to measure the entire spectrum.
The most complete information is obtained by measuring the entire visible spectrum. A spectroradiometer measures radiant spectra; a spectrophotometer measures reflective spectra. Having the spectrum allows the user to compute tristimulus values under any viewing condition. To measure the spectrum requires that the spectrum...
