From Photon to Pixel

6Image Quality

The quality of the images produced by a camera is a key concern for photographers, but the subject is a particularly complex one. Quality assessment needs to take account of a variety of measurable technical aspects, associated with the performance of the technologies involved (see Chapters 2 and 3). It also involves perceptual considerations, which are more or less clearly understood; these are often standardized, using the notion of a standard observer (Chapters 4 and 5). However, the notion of quality is based predominantly on highly subjective esthetic criteria, which are generally cultural, linked to both the scene and the conditions in which it is viewed, and highly dependent on observers themselves. These subjective and cultural criteria have led photography to be considered as an art, with academies, museums, exhibitions, etc.; quality should, therefore, be judged using the criteria of this art. In the context of this work, however, we will simply examine the technical aspects of quality, along with their psychovisual effects via the properties of human perception, as we understand it.

In section 6.1, we will begin by considering the criteria used by engineers in order to measure image quality: the signal-to-noise ratio, resolution, transfer function, sharpness and acutance. These quantities are those used in works on photographic materials; our intention here is to provide readers with the vocabulary necessary to interpret test results using these analytical ...