Exercise 3 solution

Output (run): gains about [1.53, 1.15, 0.68]
(90, 120, 200)  -> (138, 138, 135)
(60, 80, 140)   -> (92, 92, 95)

Red is boosted (gain 1.53), green slightly boosted (1.15), blue reduced (0.68). The scene had a blue cast, as under a cool light source such as an overcast sky or shade (Chapter 4: overcast about 6,500 K; the camera article's shade preset about 8,000 K). The results are almost grey but not exactly, because the made-up pixels do not have identical casts; rounding also matters.