Essential characteristics of noise  Sunday, May 10, 2009  Camera
Article  At higher light levels, another phenomenon appears.
Each pixel has its own analog gain factor, which is directly
related to the physical size of certain capacitors. This
phenomenon is called Pixel Response Non-Uniformity (PRNU).  The
resulting noise can be modeled as additive, with a standard
deviation proportional to the signal, i.e., . The SNR in the
highlight is approximately  where is a constant which is
characteristic of pixel non-uniformity.  This implies that the
SNR does not increase further when PRNU becomes the main source
of noise (which could always happen because PRNU increases
faster than photonic noise). However, sensors always have a
saturation value and PRNU is usually not the dominant source of
noise at this value. Moreover, PRNU is a fix bias and can be
compensated for with a calibration.  Color sensitivity is an
integral value over the whole curve characteristic. In
particular it depends on the noise in highlights. H