[Elphel-support] linescan & artefacts

[Andrey Filippov]

> the pattern changes depending on which line-pair is used. but the output is
> not necessarily any better...
>
> I see. So it looks like pixel fixed-pattern noise. There are two ways how
to fight it.

 One is to resurrect another part of unused FPGA code - the one that can
subtract/multiply the fixed values from the image pixels (that will also
need some calibration).
 Second - with post-processing. In that case you should rather use jp46
format where pixels are not interpolated. First step - eliminate additive
parameter - you can get it if you average multiple line pairs of the grey
card or (even better) - disable autoexposure and white balance (if you use
them) and close the lens. For such measurements you need to un-apply gamma
(you can do it in ImageJ plugin) so the background subtraction will take
place with linear pixel values (setting gamma=1 in the camera would kill the
dynamic range)

Andrey
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