7. Contrast
7.1 Definition
When we observe an object, either visually or with an optical instrument, we perceive it by its apparent luminance. However, this object is never present against a black background, so it stands out against this background, which also has a perceptible apparent luminance.
Given two sources of luminances L
1
and L
2
, we can define two quantities characterizing the contrast of source 1 with respect to source 2 :
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