Wednesday, August 29, 2012

How to Measure PTC

Albert Theuwissen explains how to measure and interpret the Photon Transfer Curve (PTC) in his latest blog post.


  1. What are the reasons for a deviation from a slope of 0.5 in standard deviation versus mean log-log plot? PRNU, non-linearities, others?

  2. Hi, PRNU does not play a role, because the noise calculation takes only temporal noise into account. Non-linearity plays a role (you can see that also in the mean-variance plot), but more important is the limited dynamic range. In the mean-standard deviation plot you can observe that the curve is getting steeper and steeper if you move to larger effective output signals. So the curve has the tendency to reach a slope of 0.5 but right before coming to this point, the pixels saturate.
    Do you need more info about this effect ? I do have images and data available of devices with a larger dynamic range, and in that case getting a slope of 0.5 is no issue.


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