PRNU (Photoresponse non-uniformity)

Each of the photodiodes arrayed in an image sensor is carefully fabricated to provide uniform performance, but each also exhibits some small nonuniformity in terms of sensitivity. This may be due to crystal flaws in the silicon substrate, variations in the wafer process and diffusion in the manufacturing process. This non-uniformity is often called the Photoresponse non-uniformity.


An electron emitted from a substance by the photoelectric effect. In the field of scientific camera, a photoelectron is an electron converted from an incident photon in a pixel of an image sensor.


Light is not a continuous flow of energy. It is a stream of particles with energy called photons.

Optical measurement with a scientific camera involves capturing photons and converting photons into electron (this electron is called “photoelectron”) in an image sensor.

Photon number resolving mode

Photon number resolving (PNR) is a technique that output the precise number of photoelectrons converted from photons coming into the photodetector.

The qCMOS camera has a photon number resolving mode which can output the photoelectron number in each pixel by adapting the photon number resolving method inside the camera.

Please refer to this link, if you would like to investigate the photon number resolving mode further. 

Photon shot noise

The actual photons fly randomly in time and space due to a statistical nature of a light source.

When we collect a photon stream in multiple frames, the histogram of photon number in the frames has Poisson distribution, not delta function. This noise due to the statistical nature of the light source is called “photon shot noise”. The standard deviation of the photon shot noise σshot noise is equal to the square root of the average photon number N.

\[ \sigma_{shot\ noise} = \sqrt{N} \]

Distribution of photons

Please refer to this link if you would like to investigate the noise further.