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Humboldt-Universität zu Berlin - Faculty of Mathematics and Natural Sciences - Strukturforschung / Elektronenmikroskopie

MTF Estimate

The MATLAB programs MTFEstimate and MTFEstimate_lite estimate the modulation transfer function (MTF) of the CCD camera. They do so from a simple shadow image of the beam blocker, and completely automatic. The MTF is retrieved beyond the Nyquist frequency. How far beyond the Nyquist frequency depends on the beam blocker’s quality: for a smooth beam blocker, like the GIF entrance aperture, the MTF can be estimated up to 2 times the Nyquist frequency, see below.

The inner workings of the programs are described in Microscopy and Microanalysis 18 (2012) 336–342, and the programs are available for free upon request per email. Contact info.

On the right, three different beam blockers on three different microscopes are depicted. Note the wide variety in shape and size. The upper two beam blockers are relatively unsmooth, resulting in an inaccurate MTF estimate at frequencies above 1.6 times the Nyquist frequency. The lower beam blocker is very smooth, resulting in an accurate MTF estimate for frequencies all the way up to 2 times the Nyquist frequency.

Below, the three MTF estimates are displayed. No manual tuning was required, the program only needs the shadow images as input. The x-axes are in units of sample frequency, which is half of the Nyquist frequency.