The term appearance (see 3.2.1) implies the essential presence of human visual observations. The results of visual observation involve not only the step of observing, accomplished by the eye, but also the inseparable step of interpretation in the brain. Instrumental test methods currently cannot duplicate this second step, and therefore can now only approximate, but not fully measure, appearance. Such instrumental measures of appearance properties are useful only to the extent that they can be correlated to the results of visual observations by observers of the appearance phenomena being evaluated.

Almost invariably, too little attention has been paid to ensuring that the essential visual observations have been properly obtained to provide the basis for correlating visual and instrumental test results. (The only recent book devoted to visual measurements (1)³ has no index entry for observer.)

This guide provides the means for assessing observers, by outlining the requirements and tests for their selection, evaluation, and training. This guide should be useful to all experimenters designing or using visual test methods to provide either direct results in terms of the observation of appearance properties, or the experiments correlating such results with instrumental measures approximating the same appearance properties.

1.1 This guide describes criteria and tests for selecting, evaluating, and training human visual-sensory observers for tasks involving the perception and scaling of properties and phenomena relating to appearance.

1.2 Examples of tests requiring the use of trained observers include but are not limited to those described in the following ASTM standards: on color, Practice D 1535 and Practice E 1360; on color difference, Practice D 1729 and Test Method D 2616; on gloss, Test Method D 4449; on metamerism, Practice D 4086; and on setting tolerances, Practice D 3134.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.