Image sensor including real-time automatic exposure control and swallowable pill including the same

An image sensor comprising:

• an array of imaging pixels arranged in a plurality of rows and columns;
• a circuit for determining the amount of light received by the array of imaging pixels during an exposure period, the determining circuit non-destructively reading pixel signals from a set of imager pixels of the array which is less than the total number of imaging pixels in the array;
• and
• a circuit for performing at least one of controlling the gain of pixel signals read from the array, and controlling the illumination period of a light source for illuminating a scene imaged by the array, in response to the determining circuit,
• wherein the determining circuit compares each of the non-destructively read pixel signals to a reference signal and provides an output indicating whether a read pixel signal has a value which exceeds the reference signal, and the performing circuit performing the at least one of controlling the gain of the read pixel signal and controlling the illumination period of light source when the number of the read pixel signals which exceed the reference signal is greater than a predetermined value and wherein the reference signal is adjusted by a reference voltage generator to compensate for supply voltage variations occurring during an exposure period and pixel readout.