Fixed-pattern noise: Difference between revisions

Revision as of 22:18, 9 February 2010

Revision as of 23:56, 25 February 2010

Line 4:

Fixed pattern noise (FPN) is a general term that identifies a temporally constant lateral non-uniformity (forming a constant pattern) in an imaging system with multiple detector or picture elements ([[pixels]]). It is characterised by the same pattern of 'hot' (brighter) and cold (darker) pixels occurring with images taken under the same illumination conditions in an imaging array. This problem arises from small differences in the individual responsitivity of the sensor array (including any local postamplification stages) that might be caused by variations in the pixel size, material or interference with the local circuitry. It might be affected by changes in the environment like different temperatures, exposure times etc.

The term "fixed pattern noise" usually refers to two parameters.<ref>Electronic Shuttering for High Speed CMOS Machine Vision Applications http://www.automaatioseura.fi/jaostot/mvn/mvn2007/parameter.html</ref>. One is the '''DSNU''' ([[dark signal non-uniformity]], which is the '''offset''' from the average across the imaging array at a particular setting (temperature, integration time) but no external illumination and the '''PRNU''' ([[photo response non-uniformity]]), which describes the '''gain''' or ratio between optical power on a pixel versus the electrical signal output. Latter can be described as the local, pixel dependent '''[[photo response non-linearity]]''' (PRNL) and is often simplified as a single value measured at almost saturation level to permit a linear approximation of the non-linear pixel response.

Sometimes pixel noise <ref>Commercial Sensor Survey Radiation Testing Progress Report http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/40825/1/08-22.pdf</ref> as the average deviation from the array average under different illumination and temperature conditions is specified. Pixel noise therefore gives a number (commonly expressed in [[rms]] that identifies FPN in all permitted imaging conditions, which might strongly deteriorate if additional electrical gain (and noise) is included.