Previous version of this page can now be found here: [wiki:DetectorLinearityArchive]

== Detector Linearity ==

The final linearity correction is actually more of a flux dependent bias level.  The method used to generate the correction data was:
 1. Run ppImage on input flat images with nothing but the OVERSCAN correction enabled.
 1. Measure cell and edge row/column median values.
 1. Foreach chip/cell/region/observation date, find the best fit trend `f_region = gain * t_exp + bias_0` over a range of exposure times `3 < t_exp < 12`.
 1. Define the expected model value as `MODEL = gain * t_exp` and correction `CORR = f_region - (gain * t_exp)`. This ensures that the bias offset bias_0 is included in the correction.
 1. Foreach exptime/chip/cell/region, take the median of all correction values and fluxes, and write the table of `(flux,correction)` pairs.
 1. Apply the correction by linear interpolation of the pairs for the appropriate chip/cell/region.

I have attached two images that show the original overscan corrected image and the linearity corrected version of this image.  These two images are from 2009-12-30 and 2010-11-23, showing that the correction is stable.

[[Image(o5195g0377o_XY24.png, 800px)]]

[[Image(o5523g0616o_XY24.png, 800px)]]