A proportional counting circuit generates count values for use in variably adjusting
gain and exposure time of an image sensor array. The count values are adjusted
in proportion to the current count value. This technique allows for fast and accurate
adjustment of gain and exposure time without sacrificing the visual performance
defined by the contrast difference. At least one break-in signal disables counting
in some lower bits when a particular higher bit is asserted and allows the count
values to be adjusted by a different increment when the count value reaches a predetermined
value by asserting the particular higher bit. Break-out signals are used in less
significant bits to disable counting in all lower bits than the bit being disabled
by the break-in signal from the more significant bit.