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==== Spatial Frequency Units ====
**Units and Applications of Spatial Frequency**\\
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**Conversion Formulas**\\
Different units can be converted using parameters such as image height and focal length. The conversion formulas are as follows:
^ Unit ^ Conversion Formula ^
| Cycles / Pixel (C/P) |  |
| Cycles / Distance (cycles / mm or cycles / inch) | $\frac{MTF(C/P)}{\text{pixel pitch}}$ |
| Line Widths / Picture Height (LW / PH) | $2 \times MTF\left(\frac{LP}{PH}\right)$  ; $2 \times MTF\left(\frac{C}{P}\right) \times PH$ |
| Line Pairs / Picture Height (LP / PH) | $MTF\left(\frac{LW}{PH}\right)/2$ ; $MTF\left(\frac{C}{P}\right) \times PH$ |
| Angular Frequency (Cycles / milliradian) | $0.001 \times MTF\left(\frac{\text{cycles}}{\text{mm}}\right) \times FL(\text{mm})$ |
| Cycles / Degree | $\frac{\pi}{180} \times MTF\left(\frac{\text{cycles}}{\text{mm}}\right) \times FL(\text{mm})$ |
| Cycles / Object mm | $MTF\left(\frac{\text{Cycles}}{\text{Distance}}\right) \times |\text{Magnification}|$ |
| Line Widths / Feature Height (Px) | $2 \times MTF\left(\frac{C}{P}\right) \times \text{Feature Height}$ |
| Line Pairs / Feature Height (Px) | $MTF\left(\frac{C}{P}\right) \times \text{Feature Height}$ |
where PH = picture height (in pixels); FL (mm) = lens focal length in mm; Pixel pitch = distance per pixel = 1 / (pixels per distance).\\

**How to Change the Result Units in RIQA Software?**\\
Open the RIQA software, click "Settings", select "Global Settings", and then modify the "Display Unit" according to your needs to change the units of the output results.
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