The present disclosure relates to a readout circuit of a pixel array comprising: a first analog to digital converter coupled to a first column line of the pixel array and configured to convert a reference voltage level and a captured voltage level of a first pixel based on a first conversion gain of the first pixel; and a second analog to digital converter coupled to the first column line of the pixel array and configured to convert a reference voltage level and a captured voltage level of the first pixel based on a second conversion gain of the first pixel, the first and second conversion gains being different from each other.