Figure 13.9 Although it has the same endpoints shown in the linearly-scaled image in Figure 13.8, gamma scaling (with gamma = 2) brightens the middle tones that contain the image of the nebula. Gamma scaling is effective for relatively gentle enhancement of deep-sky objects.
/'black <P < Avh„e ^f(p) = (P ~P^V^' ^ ^ 13'6>
7? ^Pwhite->/(/>) =JPmax where /?hlatk is the black endpoint, /;whl[e is the white endpoint, and pmax is the top of the range of pixel values. To evaluate a linear look-up table between endpoints, the computer carries out the following procedure:
PROCEDURE LINEAR (pvblack, pvwhite, LUT()) slope = (pvwhite - pvblack) / pvraax FOR pv = 0 TO pvmax SELECT CASE pv
CASE pv <= pvblack
LUT(i) = ((pv - pvblack) / slope) CASE pv >= pvwhite LUT(i) = pvmax
END SELECT NEXT pv
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