An image sensor has a plurality of pixels, each pixel having a photodiode (12), a voltage amplifier (16) having gain magnitude greater than 1 and a sampling capacitor (18) charged by the voltage amplifier. In this arrangement, each pixel provides gain through voltage amplification. This enables the sampling capacitor to be kept to a low size, so that the pixel circuitry occupies the smallest possible space, thereby enabling large aperture pixels to be formed. A source-follower buffer transistor (49) is provided at the input to the voltage amplifier. This overcomes the effect of charge sharing resulting from the parasitic capacitances of the output transistor of the voltage amplifier.