A single photon counting image sensor and method is provided. In one aspect, the method of an image sensor includes counting through a counter circuit a number of photons detected through a photodiode when a light is incident on the photodiode. The method also includes storing in a memory circuit a time a count of the number of photons take to match a reference count of the number of photons. In another aspect, an image sensor device includes a pixel circuit. The image sensor device also includes a photodiode circuit of the pixel circuit to detect photons when a light is incident on the photodiode circuit. The image sensor device further includes a counter circuit of the pixel circuit coupled to the photodiode circuit to count a number of photons detected when a light is incident on the avalanche photo diode.