Output-compensating device for image sensor

Abstract

An output compensating device capable of optimally compensating output signals of an image sensor composed of a number of light-sensor circuits, each of which represents a unit pixel and is capable of producing in a photoelectric converting element a sensor current proportional to a quantity of light falling thereon, converting the current into a voltage signal by a MOS type transistor with a logarithmic output characteristic in a weak inverse state, initializing itself by removing a charge accumulated in a parasitic capacitor of the photoelectric converting element by changing a drain voltage of the transistor to a value lower than a normal value for a specified time and outputting a pixel signal having a logarithmic characteristic at a large quantity of the sensor current and a pixel signal having a non-logarithmic characteristic at a small quantity of the sensor current. This device has a means for compensating each pixel signal from the image sensor for an offset value and outputting a resulting signal if said signal has an output characteristic within a logarithmic response region or a non-logarithmic region depending on the output condition and, if not, further compensating the offset-compensated signal for its gain and outputting a resulting signal, thus ensuring the optimal compensation of each pixel signal of the image sensor in accordance with its output state.