Effects of threshold selection on molecule density distribution in the Z-ring.

<p>(A) Histogram (gray bars) of molecules per pixel (15 nm ×15 nm) inside the Z-ring of a simulated image that was not processed with a clustering algorithm. (B) Histogram (gray bars) of molecules per pixel of the corresponding reference image, where each molecule is represented only once. Poisson distributions simulated with the sample means, 3.9 (A) and 1.2 (B) molecules per pixel, are shown in red. The ratio of mean values reflects the localization of each molecule approximately three times due to the simulated photoblinking kinetics (blink> = 2, <τ_off> = 1 frame, <τ_on> = 1 frame). Poisson goodness-of-fit tests resulted in p_GOF = 0 for distribution in (A), suggesting that blinking results in deviations from a Poisson density distribution (p_GOF = 0.74 for the reference distribution in (B)). Insets show the cropped Z-ring regions used to generate the histograms. (C) p-values from the KS-test when the molecule density distribution of the Z-ring generated by the reference image (B) is compared with distributions in images generated with different threshold pairs. Distributions that resulted in p_KS >0.05 are not significantly different from the distribution in the reference image. Dataset analyzed is the same simulated dataset shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0051725#pone-0051725-g002" target="_blank">Figure 2</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0051725#pone-0051725-g003" target="_blank">3</a>.