"The Spatial Frequency Response (MTF), shown to twice the Nyquise frequency. The key result is MTF50, the 50% MTF frequency, which corresponds to perceived image sharpness. It is given in cycles per pixel (c/p) and line widths per picture height (LW/PH). ……" How to understand the “picture height” in these sentences. Can you help me? thanks
The picture height in this context is the height of the image. It is an output-size independent way of specifying the amount of detail contained in an image.
For example saying an image contains 2300 lines per picture height means an image has 2300 lines that fit within the height of the image (in landscape format). Regardless of whether you are looking at that image on your phone, or on a 30" display.
The other way of specifying resolution is lines per millimetre, which will obviously depend on how large you display your image.