1. An image sensor having a pixel array with a plurality of pixels in rows and columns, the image sensor comprising: a plurality of light-receiving units in the pixels in the pixel array, each light-receiving unit configured to generate a pixel signal; a signal processing unit configured to read and process the pixel signals from the light-receiving units and perform a signal process, the signal processing unit comprising a selection transistor that simultaneously selects pixels of different rows having a same color arrangement, a reset transistor that simultaneously initializes the pixels in a same column and different rows, and a transfer transistor that simultaneously transfers the pixel signals in the same column to a signal detection unit; and a timing control unit configured to turn on selection transistors of different rows to select different rows of pixels of the same color in the same column without storing previous information, simultaneously turn on the reset transistors of the different rows in the same column then simultaneously turn off the reset transistors of the different rows in the same column to initialize the corresponding pixels in the same column, then simultaneously turn on the transfer transistors in the same column then simultaneously turn off the transfer transistors in the same column to transfer the pixel signals in the same column to the signal detection unit so as to obtain an average of the pixel signals subjected to the signal process.