An electronic image sensor with a pixel array of a plurality of active pixels is provided. Each of the active pixels includes: a photo detector, providing a sensing node for producing a signal based on an amount of light incident thereon; a storing node for storing a plurality of photo-generated charges according to the signal; a first controllable potential barrier between the sensing node and the storing node; an outputting node; and a second controllable potential barrier between the storing node and the outputting node, wherein each of the sensing node, the storing node and the sampling node is not overlapped.