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 : $C=\frac{L_1-L_2}{L_2}\text{et}{C}^{\prime }=\frac{L_1-L_2}{L_1+L_2}$

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