How do I transform LP/pixel to LP/PH in MTF plot?

Question

I'm working on computing MTF plots for smartphone camera. I've a working code in Python inspired by plenty of codes found online, MATLAB, Peter Burns and his sfrmat etc.. which computes the data from a chart I've created using the slanted edge algorithm, and is displayed as Line Pairs per Pixels.
However, to compare smartphones between them, I've found that displaying the MTF plot with Line Pairs per Picture Height should be better. How can i go from one to the other ?
Also, as I extract a ROI of the chart, is the Picture Height the original one, or only of the ROI ?
Finally, I've seen on Imatest that they discuss Line Pairs per Object Distance (https://www.imatest.com/docs/sharpness/#freq_units) but I honestly don't understand it. Can someone explain it a bit ? Could it be capable of giving information on the smallest possible details distinguishable ?
Thank you already

Steven Kersting · Accepted Answer

I believe your LP/Pixel is actually cycles/pixel, which nyquist limits to a maximum of .5 (or 1 L/P). So if your result is 1 line/pixel, then the conversion to per image height is simply the height of the sensor in pixels... and LP/image height would be .5x.
I have no idea what the ROI is you are referencing... but anything useful would be based on the original image (sensor area).
LP/object distance is extremely uncommon... basically, if you kept the test target at the same distance for every lens, then the distance and magnification (lens difference) has to be included into the calculation to get a lines/mm usable/comparable type of result. What is normally done is that the target is set at different distances based on the lens' magnification, so that the lines occupy the same per mm area.

How do I transform LP/pixel to LP/PH in MTF plot?

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