PubMed · 8715016
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A Smith. 1995. Seeing the light.. https://pubmed.ncbi.nlm.nih.gov/8715016/
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Veiling glare and ambient light reflection can significantly degrade the quality of an image on a display device. Veiling glare is primarily associated with the diffuse spread of image signal caused by multiple light scattering in the emissive structure of the device. The glare ratio associated with a test image with a 1-cm-diameter black spot is reported as 555 for film, 89 for a monochrome monitor, and 25 for a color monitor. Diffuse light reflection results from ambient light entering the display surface and returning at random emission angles. The diffuse reflection coefficient (luminance/illuminance, 1/sr) is reported as 0.026 for film, 0.058 for a monochrome monitor, and 0.025 for a color monitor with an antireflective surface coating. Both processes increase the luminance in black regions and cause contrast reduction. Specular reflections interfere with detail in the displayed scene. The specular reflection coefficient (luminance/luminance) is reported as 0.011 for film, 0.041 for a monochrome monitor, and 0.021 for a color monitor with an antireflective coating.
The authors previously reported a general technique based on contrast-detail methods to provide an overall quantitative evaluation of electronic image display quality. The figure-of-merit reflecting overall display quality is called maximum threshold contrast or MTC. In this work we have optimized the MTC technique through improvements in both the test images and the figure-of-merit computation. The test images were altered to match the average luminance with that observed for clinical computed radiographic images. The figure-of-merit calculation was altered to allow for contrast-detail data with slopes not equal to -1. Preliminary experiments also were conducted to demonstrate the response of the MTC measurements to increased noise in the displayed image. MTC measurements were obtained from five observers using the improved test images displayed with maximum monitor luminance settings of 30-, 50-, and 70-ft-Lamberts. Similar measurements were obtained from two observers using test images altered by the addition of a low level of image noise. The noise-free MTC and MTC difference measurements exhibited standard deviations of 0.77 and 1.55, respectively. This indicates good measurement precision, comparable or superior to that observed using the earlier MTC technique. No statistically significant image quality differences versus maximum monitor luminance were seen. The noise-added MTC measurements were greater than the noise-free values by an average of 4.08 pixel values, and this difference was statistically significant. This response is qualitatively correct, and is judged to indicate good sensitivity of the MTC measurement to increased noise levels.
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