Under-exposed

ppl. a. (Stress var.) Photogr. [UNDER-¹ 10 a.] Of a sensitized plate or film: Having received too short an exposure to light.

1861.  in Wylde’s Circ. Sci. (1865), I. 162. This is an … advantage when the picture is under-exposed.

1878.  Abney, Photogr., 81. An under-exposed picture will develop very slowly.