a pixel array uses two sets of pixels to provide accurate exposure control . one set of pixels provide continuous output signals for automatic light control as the other set integrates and captures an image . alc pixels allow monitoring of multiple pixels of an array to obtain sample data indicating the amount of light reaching the array , while allowing the other pixels to provide proper image data . a small percentage of the pixels in an array is replaced with alc pixels and the array has two reset lines for each row ; one line controls the reset for the image capture pixels while the other line controls the reset for the alc pixels . in the columns , at least one extra control signal is used for the sampling of the reset level for the alc pixels , which happens later than the sampling of the reset level for the image capture pixels .