hello,

i hope you are doing well.

We are working with Pylinac on the Catphan test and we want to compare the “low contrast visibility” value with the one we obtained using ImageJ. The formula we use in our department is shown in the image below, and we would like to know the formula that Pylinac uses for the calculation. The problem is that the formula we found in the documentation is not clear enough( Contrast - pylinac 3.11.0 documentation ). Can you provide us with more details or adapt our formula to yours?

Best regards

Kaoutar

Kaoutar,

You are free to use whatever formula you wish for low contrast. Pylinac tries to use equations supported by literature or commonly accepted. If you have peer-reviewed paper with these formulas please link it and I’ll read up on it.

I’m afraid I don’t know how I could be clearer about the formulas pylinac uses. They are commonly used formulas. Your equation seems to mostly match the contrast-to-noise definition here: Contrast-to-noise ratio - Wikipedia

Pylinac does do contrast-to-noise, but assumes contrast is calculated with one of the described equations. There is currently no “difference” equation simply subtracting one signal from the other like the numerator of the CNR wikipedia definition, but I can add that as a contrast algorithm type.