In an image processing system, the imager gain and the exposure time are
adjusted based on a predefined stepping sequence using a stepping table
designed to maximize the signal-to-noise ratio in the image. This is
achieved by providing a stepping sequence with each step having the
largest suitable integration time (exposure) and an appropriate amplifier
and digital gain setting, while achieving an equal relative percentage
change in image brightness between adjacent sequence steps. The size of
the executed AE steps is proportional to the distance between a current
image luminance and the target luminance. This is achieved by the
capability to skip one or more steps in the stepping sequence, if
appropriate, for each relevant executed step, with the number of skipped
steps, if any, being proportional to the magnitude of the deviation from
the target brightness.