On Saturday, March 22, 2014 11:40:21 PM UTC+8, Mikko OH2HVJ wrote:   
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   >   
   > > I repeat the test for various exposure durations under the same light   
   >   
   > > and do a linear regression on pixel values. The linearity of the   
   >   
   > > pixels are very good but they do not cross from zero, the regression   
   >   
   > > line has a DC offset.   
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   >   
   >   
   > There's a bias voltage in the sensor output signal by both the   
   >   
   > chip amplifiers and purposefully added so that AD converter   
   >   
   > does not have to start from zero, where it may be non-linear.   
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   >   
   >   
   > This is removed in astronomy by taking 'bias images' in dark with   
   >   
   > zero exposure time and substracting this from the image.   
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   >   
   >   
   > --   
   >   
   > Mikko OH2HVJ   
      
   Mikko, I do this. If you look at my description, I first measure FPN and take   
   it out. Despite this I see a DC offset later which makes me wonder.   
      
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