5.1 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.

5.2 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.

5.3 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. The user is cautioned to avoid the substitution of validated vision tests with replicas of any kind, either printed, photographed or digitally displayed.

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 D1535 and Practice E1360; on color difference, Practice D1729 and Test Method D2616; on gloss, Test Method D4449; on metamerism, Practice D4086; and on setting tolerances, Practice D3134.

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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.