un·der·ex·pose 
(ŭn′dər-ĭk-spōz)
(ŭn′dər-ĭk-spōz)tr.v. un·der·ex·posed, un·der·ex·pos·ing, un·der·ex·pos·es
To expose (film) to light for too short a time or to light or radiation that is insufficient to produce normal image contrast.
un′der·ex·posure (-ĭk-spōzhər) n.