FIGURE 1.

Computation of the thinness ratio. (A) Confocal maximum intensity projection image of a mito-DsRed2-expressing cortical neuron; original image (G(x,y)) and the absolute value of its discrete Fourier transform The maximal spatial frequency of the Fourier transform was 1/(2 × 0.075μm) = 6.67cycles/μm, where 0.075 μm is the pixel size in the space domain. For better visualization, ω is cropped at 4 c/μm. (B and C) HBP (B) and LBP (C) filter and transfer functions, f_filter(ω) and correspond to Eqs. 4 and 2, respectively. The theoretical MTF(ω) for confocal microscopy is shown by the red trace (NA = 1.3, λ = 590 nm, n_medium = 1.33, d_pinhole = 1.2 Airy units or resels (1 resel = 0.61λ/NA); see Eqs. S1–S6 and Figs. S1 and S2 in Data S1). (D and E) Fluorescence images after filtering (). Intensities can be directly measured by averaging pixel values in regions of interest, as indicated by the red dashed line. Scale bar, 5 μm. Fluorescence intensity is given in photoelectrons (the used gain settings resulted in 1.9 gray value units/photoelectron). Images are printed at γ = 1.6. See example for filtering in Data S2.