There is a confusion about spatial resolution in different standards. Sometimes it is the spatial resolution of the system and in other conditions it is the spatial resolution of the detector. And then there is the Basic Spatial Resolution SRb. To get a more consistent terminology, the SR is added with footnotes.
Example:
is the basic spatial resolution of the image.If the spatial resolution of the detector is used, replace "image" with "detector"; if the system resolution is meant, replace "image" with "system".
And - if this wouldn't be enough to increase confusion, there is another version:
This is the "interpolated Basic Spatial Resolution of a Detector", the version with the more precise method using an interpolation approximation between the resolved dips in the line profile.
"The iSRb detector is calculated as the second order polynomial approximation of the modulation depth (dip) versus the wire pair spacing of neighbored wire pairs with at least two wire pairs with more than 20 % dip between the wires in the profile, and at least two wire pairs with less than 20 % dip between the wires in the profile, if their values are larger than zero. If no values are available with dip less than 20%, one the next wire pair value with the dip of zero shall be used."
Most of the SR versions are explained in ASTM E1316 - Terminology - pages 14 and 16
In Europe the expression "Unsharpness" is more polular compared to the spatial resolution in North America. It can be converted very easily:
Unsharpness = 2* Spatial Resolution
Unsharpness is given with the contrast of dark - bright - dark (similar to line pairs/mm).
Spatial Resolution is given with the contrast of a line bright - dark (similar to lines pairs/mm).
The other conversion is from linepair values to unsharpness or spatial resolution. Let us take an example:
A resolved 100µm wire pair of a duplex wire gauge has
- 200µm Image Unsharpness
- 100µm Spatial Resolution == 0.5*Image Unsharpness
- 5 LinePairs/mm == 1000 / Image Unsharpness in [µm] (or 1 / Image Unsharpness in [mm])
A detailed list of conversions can be taken out of ASTM E2002 Table 1.