[Elphel-support] raw file from elphel

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---- On Sun, 14 Oct 2012 00:02:50 -0700 Venkat Subbiah<venkat at magnasinc.com> wrote ---- 

 > Andrey,
 > 
 > 
 > Thanks for you reply.
 > 
 > 
 > I would like to get the pixels before any color processing. 

Venkat, that is exactly the purpose of the JP4 format

> Other than compression are the raw pixels processed before putting the data into the JP4 file?
> If so what is the kind of processing is done?

Each of the color channels is non-linearly converted to match the pixel representation with the noise caused by the quantum nature of the detection of light. I tried to explain it in http://www3.elphel.com/linuxdevices/articles/AT9913651997.html . We measured that the Aptina sensors we use have the full well capacity (number of electrons each pixel can accomodate before saturation) about 8,500e- , so the shot noise in the bright areas is ~90e- or 45 counts of the 12-bit ADC. The sensor has very low readount noise, so throwing away least significant bits would have no effect on ligh areas, but would jeopardize performance in the dark areas. Non-linear encoding allows to store 12-bit ADC data in 8 bits, keeping error below the sensor noise (predominantly shot noise) for all the range. 

Andrey