Klaus edited Method.tex  over 8 years ago

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  %\subsection{Data processing}  The frames containing single photon events were processed with the ThunderSTORM \cite{Ovesny2014} superresolution imaging plug-in for ImageJ. Due to memory limitations, the USAF data was processed in 6$\times$5,000 and the cell data in 3$\times$2,000 image stacks. The software first detects the events from the noise background, and an approximate localization algorithm locates the center pixel of each event. The peaked pulseheight distribution of the photon events \cite{Hirvonen2014a} \cite{Hirvonen2014_rsi}  makes the setting of a threshold relatively straight-forward. A sub-pixel localization algorithm then calculates the center of the events with greater resolution. The software camera parameters were set to 80.0~nm pixel size and 36 photoelectrons per A/D count. The base level varied between image stacks due to fluctuations in the EBCCD temperature, and was set to the average minimum grey value for the image stack in the range of 100-140 A/D counts. A wavelet (b-spline) image filter was applied with order of 3 and scale of 2.0. For the approximate localization of the events, centroid of connected components method was used with a peak intensity threshold (PIT) of 2*std(Wave.F1) for the USAF data, and a PIT of 1.5*std(Wave.F1) for cell data, with watershed algorithm enabled for all data. 

Least squares (LS) fitting method was also tested with integrated Gaussian (IG) PSF with 3 pixel fitting radius and 1.6 pixel SD, and radial symmetry localisation method with 2 pixel estimation radius.