An adaptive contrast enhancement (ACE) method and apparatus provide a
natural enhancement in accordance with the time-varying characteristics
of a video sequence. Characteristics of a time varying video sequence are
specified and a nonlinear transform over the input video sequence is
performed to enhance mainly the contrast of the input. A probability
density function (PDF) of a time varying input video sequence is computed
and then some predetermined video parameters relating to contrast is
extracted from the PDF. Based upon the extracted video parameters, a
nonlinear transform function is then constructed and updated as a look up
table (LUT), which is synchronized with the associated video picture or
field SYNC signal. The transform LUT is then applied to the input video
to provide an enhanced video output signal.