an image sensor is proposed , which can output different amount of data according to different resolution modes . the image sensor employs a plurality of photo diodes to convert received optical signals into charges and uses a plurality of sets of transfer gates to move out the charges on the photo diodes . the image sensor uses a plurality of shift registers to receive the charges moved out from the transfer gates and to remove the charges according to two sets of control signals . a floating diffusion node is used to receive the charges on the shift registers for generating electrical signals . the image sensor uses a charge control unit to control whether the output charges from the shift registers are passed onto the floating diffusion node . because the image sensor uses the charge control unit to control all , ½ or ¼ parts of charges into the floating diffusion node , a scanner with the image sensor can obtain a high quality image when scanning in high resolution modes and run at a high speed when scanning in low resolution modes .