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Measurement of a small black area on a white electronic display screen is often accompanied by serious contamination from veiling glare in the detector. The black measurement can be thousands of percent in error. Character-stroke-contrast or small-area-contrast measurements are greatly improved by using a replica mask of known luminance even in uniform ambient conditions.
Kelley, E.
(2009),
Character contrast, Information Display Magazine, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=901128
(Accessed June 8, 2023)