Consider a display with following specifications: γ = 2.2, Lpeak = 500 cd/m2 , Lblack = 0.5 cd/m2 and k = 0.01. Then, determine the dynamic range of this display: (a) In a dark room (Eambient ≈ 0) (b) In outdoor settings (Eambient = 10000) Does a comparison of the computed dynamic ranges help to provide insights as to why a fairly low ambient light setting during screening of the movies?
Question
Consider a display with following specifications: γ = 2.2, Lpeak = 500 cd/m2
, Lblack = 0.5 cd/m2 and
k = 0.01. Then, determine the dynamic range of this display: (a) In a dark room (Eambient ≈ 0) (b) In outdoor settings (Eambient = 10000) Does a comparison of the computed dynamic ranges help to provide insights as to why a fairly low ambient light setting during screening of the movies?
Solution
The dynamic range of a display is the ratio of the maximum (Lpeak) to the minimum (Lblack) luminance values that the display can produce. It is often expressed in decibels (dB), where dynamic range (dB) = 20 log10 (Lpeak / Lblack).
(a) In a dark room (Eambient ≈ 0)
The dynamic range is simply the ratio of Lpeak to Lblack.
Dynamic Range = Lpeak / Lblack = 500 cd/m2 / 0.5 cd/m2 = 1000
To express this in decibels, we use the formula:
Dynamic Range (dB) = 20 log10 (Dynamic Range) = 20 log10 (1000) = 60 dB
(b) In outdoor settings (Eambient = 10000)
The dynamic range is affected by the ambient light, which adds to the black level. The effective black level Leff is given by Leff = Lblack + k * Eambient.
Leff = Lblack + k * Eambient = 0.5 cd/m2 + 0.01 * 10000 = 100.5 cd/m2
The dynamic range is then:
Dynamic Range = Lpeak / Leff = 500 cd/m2 / 100.5 cd/m2 = 4.98
In decibels, this is:
Dynamic Range (dB) = 20 log10 (Dynamic Range) = 20 log10 (4.98) = 13.97 dB
The comparison of the computed dynamic ranges shows that the dynamic range is much higher in a dark room than in outdoor settings. This is because the ambient light increases the effective black level, reducing the contrast between the black and peak levels. This is why a fairly low ambient light setting is preferred during the screening of movies, as it allows for a higher dynamic range and better contrast.
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