an amplifier, configured to amplify a first image signal by a first analog gain and to amplify a second image signal by a second analog gain, wherein the first image signal and the second image signal are generated by a pixel array of an image sensor, wherein each one of pixel circuits of the pixel array comprises a first capacitor for generating the first image signal and a second capacitor for generating the second image signal, wherein a charge storage capacity of the first capacitor is smaller than a charge storage capacity of the second capacitor; and

a gain control circuit, coupled to the amplifier, configured to selectively set the first analog gain to one of a first gain value and a second gain value, or to selectively set the second analog gain to one of a third gain value and a fourth gain value, wherein the first gain value is larger than the second gain value, and the third gain value is larger than the fourth gain value;

wherein each one of the pixel circuits has a first conversion gain corresponding to the first capacitor and a second conversion gain corresponding to the second capacitor.