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 .