Line pairs per millimeter lp/mm
widths/picture height LW/PH
Modulation Transfer Function (MTF) Spatial Frequency Response (SFR)
Green is for geeks.
Experience has shown that the best indicators of image sharpness are the spatial frequencies where MTF is 50% of its low frequency value (MTF50) or 50% of its peak value (MTF50P).
line pairs per millimeter (lp/mm) x Line widths per picture height (LW/PH) 2 * lp/mm * (picture height in mm) cycles per pixel C/P
Imatest (Upper-left) A narrow image that illustrates the tones of the averaged edge. It is aligned with the average edge profile (spatial domain) plot,immediately below. Average Edge (Spatial domain):
MTF (Frequency domain): MTF50
MTF at Nyquist
Imatest 3.6+ Lens MTF response
system MTF response often exceeds it
MTF50(Line Widths ⁄ inch on the print) =
MTF50(LW ⁄ PH) Print height in inches
The ideal response would have high MTF below the Nyquist frequency and low MTF at and above it.
Slanted edge algorithm (calculation details) ISO standard SFR