Fixed-pattern noise: Difference between revisions

Revision as of 23:56, 25 February 2010

Revision as of 23:57, 25 February 2010

Line 5:

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.

In practice, a long exposure (integration time) emphasizes the inherent differences in pixel response so they may become a visible defect, degrading the image. Although FPN does not change appreciably across a series of captures, it may vary with integration time, imager temperature, imager gain and incident illumination, it is not expressed in a random (uncorrelated or changing) spatial distribution, occurring only at certain, fixed pixel locations.