An image display system comprises a pixel driving circuit. A storage capacitor is coupled between the first and second nodes. The first switch is turned on in the first and second periods. The second switch, coupled to the first node, is turned on in the first and second periods. The third switch, coupled between the second node and the first switch, is turned on in the first, third and fourth periods. The fourth switch, coupled between the second switch and the first voltage, is turned on in the first, third and fourth periods. The fifth switch, coupled between the second node and the first voltage, is turned on in the first, second and third periods. The sixth switch, coupled between the first node and the reference voltage, is turned on in the fourth period. The first transistor is coupled between the first and second switches and is turned on in the fourth period. During the second period, the voltage between source and gate of the first transistor is a threshold voltage. The electroluminescent element emits light in the fourth period.