The purpose of a display device is to convey information to an observer with minimal alteration of its content. All display devices present the information as a modulated luminance map that is associated with the data in the input signal according to a display presentation function. The amount of information detail (i.e., diagnostic information) to be displayed typically determines the quality with which the device must transfer digital values into luminance output. For instance, an alphanumeric device with only seven pixels can display numbers and letters reasonably well on
a billboard. When the amount of information to be displayed increases in spatial detail and intensity variations, some degradation in the image quality conveyed to the observer is unavoidable. This is particularly true for some digital medical imaging modalities where large pixel arrays are acquired with a very large image value luminance range.
When electronic displays are used to present large amounts of information (for instance, in digital medical imaging systems for mammography and chest radiography), the image quality requirements are no longer defined by the information content, but instead by the capabilities of the observer to successfully accomplish the visual task. It is therefore essential for those interested in studying the display of high-information content images in electronic devices to understand the observer’s limitations. In this chapter, we review aspects of the human visual system relevant to the high-fidelity display requirements of contrast, luminance range, and resolution.
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