Objective spectrophotometric color

Objective spectrophotometric color measurement, as described in AOCS Official Method Cc 13 50 (Firestone, 1998), gives results that are in general highly correlated with Lovibond color, although wide discrepancies occur with some oils (O Brien, 2003). Method Cc 13-50 is stated to be applicable to cottonseed, soybean and peanut oils, and requires revision to accommodate the use of double beam spectrophotometers. Its applicability to milk fat is not known. 

Spectrophotometric color data are generated to fulfill the colorist s desire to have a nonbiased, common scale by which to compare different observations, that is, numbers interpreted as objective facts. 

The indirect methods discussed thus far have dealt with measurement of color only as it can be correlated with physical characteristics of materials and the effect of these materials on radiant energy. As has been pointed out, the reflectance spectro-photometric curve describes a property of the material. A change in the reflectance spectrophotometric properties may not always result in a change in visual color. The reason is that color of the object is not an unchangeable characteristic of the object itself, dependent only upon these reflectance properties, but is also dependent upon the quality of the illuminating light and the sensitivity of the observer s eye. Thus the measurement and description of visual color are psychophysical problems... 

Objective Evaluation of Color. In recent years a method has been devised and internationally adopted (International Commission on Illumination, I.C.I.) that makes possible objective specification of color in terms of equivalent stimuli. It provides a common language for description of the color of an object illuminated by a standard illuminant and viewed by a standard observer (H). Reflectance spectro-photometric curves, such as those described above, provide the necessary data. The results are expressed in one of two systems the tristimulus system in which the equivalent stimulus is a mixture of three standard primaries, or the heterogeneous-homogeneous system in which the equivalent stimulus is a mixture of light from a standard heterogeneous illuminant and a pure spectrum color (dominant wave-length-purity system). These systems provide a means of expressing the objective time-constant spectrophotometric results in numerical form, more suitable for tabulation and correlation studies. In the application to food work, the necessary experimental data have been obtained with spectrophotometers or certain photoelectric colorimeters. 

Figure 6-1 Spectrophotometric Curves of Colored Objects. Source From Hunter Associates Lab., Inc.

ASTM, E1164 Standard Practice for Obtaining Spectrophotometric Data for Object-Color... 

---