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Perceptual Fidelity for Digital Image Display

Kate Devlin, Perceptual Fidelity for Digital Image Display. PhD thesis. Univeristy of Bristol. April 2004. PDF, 2966 Kbytes.

Abstract

Many applications (such as medical imaging or digital heritage) require that the original version of an image will appear the same regardless of where or how it is displayed. However, the conditions in which an image is displayed can adversely affect its appearance. Computer monitor screens not only emit light, but can also reflect extraneous light present in the viewing environment. This can cause images displayed on a monitor to appear faded by reducing their perceived contrast. Current approaches to this problem involve measuring this ambient illumination with specialised hardware, then altering the display device or changing the viewing conditions. This is not only impractical, but also costly and time consuming. For a user who does not have the equipment, expertise or budget to control these facets of image display, a practical alternative is sought. This thesis presents a method whereby the display device itself can be used to determine the effect of ambient light on perceived contrast, thus enabling the viewers themselves to perform visually-based calibration. This method is grounded in established psychophysical experimentation, and we present both an extensive procedure and an equivalent rapid procedure. Our work is extended by providing a novel method of contrast correction so that the contrast of an image viewed in bright conditions can be corrected to appear the same as an image viewed in a darkened room. This is verified through formal psychophysical validation studies. These methods and algorithms are easy to apply in practical settings, while accurate enough to be useful.

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