Fig. 4
From: Modified Pearson correlation coefficient for two-color imaging in spherocylindrical cells
a Experimental 2D localization probability density maps of 8436 HU–PAmcherry molecules (Top) and 6570 RNAP–YFP molecules (Bottom). Composite of data from 11 cells of tip-to-tip length Lcell in the range 3.6 to 3.8 μm. The color scale indicates the number of molecules in each pixel. b Axial probability density distributions of the imaged molecules. c Scatter plot of individual normalized difference matrix elements for MPCC, \( {\widehat{\Delta }}_{\mathrm{ij}}^{\mathrm{HU}} \) vs. \( {\widehat{\Delta }}_{\mathrm{ij}}^{\mathrm{RNAP}} \). Plot shows significant visual evidence of positive correlation; the calculated MPCC is + 0.39. d Histogram of 200 MPCC values calculated for pairs of independent, random 3D distributions using the same number of HU and RNAP copies and the same pixelation as the experimental data. Best fit to a Gaussian curve has <MPCC> = − 0.0030 and σ = 0.061 (Black curve). The experimental MPCC (arrow) lies at + 6.4σ, making it highly improbable that two random distributions would produce such a large, positive result. e Convergence of MPCC values vs mean occupancy/pixel for simulated positive correlation (top; expected MPCC = + 1) and for experimental RNAP/HU images (bottom). Three different pixel sizes are shown: 50 nm (Np = 1178), 100 nm (Np = 279), and 200 nm (Np = 77). For the experimental data, occupancy/pixel at fixed pixel size was varied by randomly deleting red and green molecules. See Additional file 1: text, Figure S8 and Table S1 for additional information