An automatic exposure system is arranged to dynamically adjust the exposure time of a pixel array in an imaging system. A selected group of pixels from the pixel array are evaluated using a non-destructive readout procedure to determine the proper exposure time for the pixel array, while the pixel array is exposed to light that is reflected from a scene. Threshold detectors are employed to compare the signals from the selected group of pixels to a peak level that corresponds to a threshold limit for the pixels. The exposure of the pixel array is terminated when at least one pixel from the selected group of pixels exceeds the threshold limit. The threshold limit may be set to a level that is below total saturation for the pixels such that an overexposure margin is provided. Enhanced image contrast is achieved using automatic exposure time adjustment.