Disclosed is an image sensor comprising: an image sensing unit array, for sensing an object and comprising a plurality of image sensing units arranged in a sensing matrix with M rows and N columns; an image data reading circuit, for reading and outputting image data caught by at least part of the image sensing units; and a control unit for controlling the image data reading circuit to read image data for a reading region in the sensing matrix. The image sensor further comprises a buffer for storing the image data. A number for the buffer rows of the buffer can be smaller than a number for the buffer columns of the buffer to reduce the buffer size.