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Image Quality Tolerance in Context

It is relatively straightforward to determine the point at which images of reduced quality become perceptibly different from the full-quality counterpart. The point varies between users, affected by physical factors, but the range is measurable. However, the same standards cannot be applied to the issue of users' tolerance.

Tolerance is a notional concept of image acceptability and, clearly, a number of variables complicate any measurement of this. It can be predicted that there would be differences in how individuals regard the issue based on personal taste and also what their relationship with the image might be at the time: do they need information from it? Do they like it? Do they even notice its presence?

In order to understand a little more of the interaction between these factors, we undertook an exploratory study. The study was not be expected to generate any definitive design criteria, rather to explore whether such criteria were appropriate or not.

Obviously, a thorough test of quality tolerance would have involved working with several different pictures drawn from different genres, presented in different contexts and evaluated in the pursuit of different tasks. Since at this point of development, the purpose in involving users was to gather indicative data, a much simpler method was sufficient. It involved presenting users with one picture in several conditions. Semi-structured questioning optimised the amount of information that could be gleaned. There were four groups of questions: user-related, image-related, time-related and product-related.

Malcolm McIlhagga
Thursday June 11 16:17:19 BST 1998