Saturation Contrast and Brightness Shift: Photoshop Paradoxes

Abstract

The essence, structure and components of full graphic contrast are considered within the informational paradigm. Basic tenets of graphic contrast information theory are stated. Concepts of visual and physical contrasts; of homogeneous and heterogeneous physical contrasts visibility functions are introduced. Lemma on the partial contrasts control is proved. As a result the system requirements to control visual perceptual contrasts are established. From this point of view, the work of the Photoshop software package contrasting toolkit has been investigated. It is shown that its <Saturation> tool in RGB Mode does not meet system requirements. The algorithm of saturation contrast conversion by similar tools is formulated. When comparing the evolution of such transformation results with those, predicted within the framework of color saturation classical phenomenology, an algorithm defect is detected – the destructive brightness shift. Its evaluation is completed, causes and conditions of its appearance are identified. Artifacts generated by the brightness defect are demonstrated and analyzed. A way to correct errors of the disclosed algorithm is proposed. The information transferred with the saturation contrast and with the contrast caused by brightness defect is compared. Practical recommendations on the contrast image analysis in the expert field are offered. The utility of Photoshop for image synthesis and image analysis problems is estimated and the direction of further efforts is outlined.