  A novel method of contrast enhancement is proposed for underexposed images,
in which heavy noise is hidden. Under low light conditions, images taken by
digital cameras have low contrast in dark or bright regions. This is due to a
limited dynamic range that imaging sensors have. For these reasons, various
contrast enhancement methods have been proposed so far. These methods, however,
have two problems: (1) The loss of details in bright regions due to
over-enhancement of contrast. (2) The noise is amplified in dark regions
because conventional enhancement methods do not consider noise included in
images. The proposed method aims to overcome these problems. In the proposed
method, a shadow-up function is applied to adaptive gamma correction with
weighting distribution, and a denoising filter is also used to avoid noise
being amplified in dark regions. As a result, the proposed method allows us not
only to enhance contrast of dark regions, but also to avoid amplifying noise,
even under strong noise environments.
