Resolition is measured using edges, Siemens stars or other regular structures with íncreasing frequencies. Units like LW/PH, LP/PH, or Cycles per pixel are independent of the sensor size and the pixel pitch.

They just take the resulting image  and its frequency content into account not caring about the size of each pixel. Dimensions like LP/mm, L/mm, or Cycles/mm require the knowledge about the sensor size / pixel pitch.

The following table and explanation will be part of the upcoming revision of ISO 12233 and was created by Don Williams.

LW/PH = Line width per picture height
LP/mm = Line pairs per millimetre
L/mm = Lines per millimetre
Cycles/mm = Cycles per millimetre
Cycles/pixel = Cycles per pixel
LP/PH = Linepairs per picture height

To convert from left column units to top row units use operation at their row/column intersection.

Spatial Frequency Unit Conversion Chart

  LW/PH LP/mm L/mm Cycles/mm Cycles/pixel LP/PH
LW/PH x 1 / [2 x picture height] / picture height / [2 x picture height] / [2 x # vert. pixel] / 2.0
LP/mm x [2 x picture height] x 1 x 2.0 x 1 x pixel pitch x [picture height]
L/mm x picture height x 0.5 x 1 x 0.5 x [pixel pitch / 2] x [picture height / 2]
Cycles/mm x [2 x picture height] x 1 x 2.0 x 1 x pixel pitch x [picture height]
Cycles/pixel x [2 x # vert. pixel] / pixel pitch x [2 / pixel pitch] / pixel pitch x 1 x [# vert. pixel]
LP/PH x 2.0 / picture height 2 / picture height / picture height / # vert. pixel x1


The pixel pitch in the 45 degree diagonal direction is not the same as in the vertical and horizontal directions. Therefore, the diagonal pixel pitch is used when applying this table to measurements in the diagonal directions

There are three planes for determination of the resolution in e.g. LP/mm. It can be in the object space, on the sensor plane or in the image with a given output magnification. In most cases the resolution on the sensor plane is the important one. To get the right value for this situation the image file should be scaled to the Sensor dimension in which case the pixel pitch on the sensor is equal to the pitch of pixels in the image file.