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What is meant when it is said a CCD's response is nonlinear? Does it mean the value of a pixel of the camera is not proportional to the number of received photons? Does it involve saturation? What factor expresses this?

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Yes, non-linear simply means the signal out isn't proportional to the light received.

CCDs are inherently very linear (until they saturate) but the readout electronics might not be, especially if the camera system isn't designed for precise scientific measurements.

Systems for TV are deliberately non-linear (see gamma correction) to allow them to show a bigger range of scenes in the limited dynamic range of a TV signal

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  • $\begingroup$ Thanks, do you know any reference where the non-linearity of the electronics is explained? $\endgroup$ – N.S. Apr 29 '17 at 18:56
  • $\begingroup$ I think you mean A/D converter by the electronics. I read in Howell's "handbook of CCD astronomy" that there are two types of non-linearity introduced by A/D converter. Did you mean that? $\endgroup$ – N.S. May 5 '17 at 10:33
  • $\begingroup$ I mean the general imperfections of all the amplifiers, ADC, signal processing etc. In a system designed to be accurate there will be small effects but in a regular TV system there will be large non-linear $\endgroup$ – Martin Beckett May 5 '17 at 12:44

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