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.