Figure 1

Figure 1   Example of a dark current histogram as determined by the variance method.  Here the dark current histogram is shifted to reflect the calculated results from the variance method.  The small distribution in the negative dark current region is the histogram of the inactive pixels.  The negative dark current is result of the shift and does not represent a real dark current.  The fitted curve is a Gaussian to give an idea of the "mean" dark current. Note that the reference (inactive) pixels could be used in this graph to determine dark current.