Conversion between sharpness frequency units

Imatest provides outputs in a default spatial frequency unit of cycles per pixel.

In the “More Settings” windows of our sharpness analysis modules, there is a dropdown menu where different frequency units can be selected. These will impact what units appear on the MTF plots. If you need to convert fr

Converting to Cycles/mm (lp/mm)

To convert from cycles/pixel to cycles/mm

Cycles/mm = (Cycles/pixel) * (1 pixel / pixel pitch in µm ) * (1000 µm / 1 mm)

for example, 0.125 cycles per pixel on a 0.7µm pixel pitch:

(0.125 cy/px) * ( 1px / 0.7 µm) * (1000 µm) =178.57 cycles/mm

Converting to Cycles/object mm

Multiply cycles/mm by the magnification. Usually this is a number much smaller than one. You can obtain magnification from a module like SFRplus, Checkerboard or eSFR ISO, or from some lens' metadata.