An image sensor includes a light-sensing element, a first transistor, and a second transistor. The light-sensing element has a first end and a second end electrically connected to a select line. The first transistor has a first end electrically connected to a first control line, a control end electrically connected to the first end, and a second end electrically connected to the first end of the light-sensing element. The second transistor has a first end electrically connected to a voltage source, a control end electrically connected to the first end of the light-sensing element, and a second end electrically connected to an output line. The light-sensing element uses the material of silicon rich oxide so that the light-sensing element can sense the luminance variance and have the characteristic of the capacitor for the level boost.