Digital Color Management: Encoding Solutions, 2nd Edition

19

A Unified Paradigm: Encoding Transformations

The preceding chapter introduced the basic principles of an appearance-based color-encoding method that is consistent with the objectives of the unified color-management paradigm. In this chapter, the colorimetric transformations required for implementation of that encoding method will be described. As was discussed previously, these colorimetric transformations are necessary to account for any differences of the original-scene, input-image, and output-image viewing conditions from the encoding reference viewing conditions.

It is important to emphasize that the colorimetric transformations do not determine how the appearance of a color stimulus, specified in terms of its colorimetry, would change if it were moved from one set of viewing conditions to another. The transformations do just the opposite; they determine how the colorimetry of the stimulus itself must be modified such that its color appearance is maintained in each different set of viewing conditions.

Although other factors also might be considered, our experience is that excellent appearance-based color encoding can be achieved if the colorimetric transformations account for each of the following factors:

• Viewing-flare contribution to observed stimuli
• Stimuli absolute luminances
• Observer chromatic adaptation
• Observer lateral-brightness adaptation
• Observer general-brightness adaptation.

In order to appropriately account for these factors, each set of image-capture, ...