| Popis: |
For many decades, professional digital imaging has faced a dilemma. On one hand, imaging scientists and engineers – and, within the last two decades, programmers – have been taught that the goal of imaging technology is the accurate “reproduction” of colour values (most commonly quantified by luminance, tristimuli, and/or chromaticity) on a display device. On the other hand, digital imaging craftspeople and artists have learned to manipulate image data as required to yield the intended visual result, objective inaccuracy notwithstanding. These approaches have been at odds owing to a fundamental aspect of colour vision: Colour appearance depends upon the visual conditions of a scene or a display (particularly, its absolute illuminance or luminance), the region surrounding the acquired portion of the scene or the displayed image, and whether the display is emissive or reflective. The dependence of perceived colour upon absolute luminance and surround conditions is well known in colour science. In the last 20 years, these visual effects have been quantified in colour appearance models, and have been standardized (in CIECAM02). However, these effects, and colour appearance theory, remain largely unknown to imaging engineers. Despite the reluctance of scientists and engineers to abandon their goal of physical accuracy, appearance effects have, in fact, been accommodated in commercially important imaging systems. However, appearance effects have been compensated largely at the level of craft, not science or engineering. Compensation of appearance effects has been subject to such confusing nomenclature and such poor documentation that it has remained mostly invisible or mysterious to the scientists and engineers. This thesis seeks to develop a systematic analysis that bridges visual psychophysics, colour appearance theory, and the practice of image signal processing in modern digital imaging systems. I analyze and document the colour appearance compensation methods that have evolved in modern digital imaging, and I link to these methods to modern psychovisual principles and to colour appearance theory. |
