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 × 0.075

*μ*m) = 6.67cycles/

*μ*m, where 0.075

*μ*m is the pixel size in the space domain. For better visualization,

*ω* is cropped at 4 c/

*μ*m. (

*B* and

*C*) HBP (

*B*) and LBP (

*C*) filter and transfer functions,

*f*_{filter}(

*ω*) and

correspond to and , 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 = 0.61

*λ*/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

*μ*m. 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.

## PubMed Commons