make the comparison using lines rather than pixels. Scan lines are the way video images are compared, so it makes sense from this viewpoint, as well.
HD Resolution
As discussed previously, standard definition and high definition refer to the amount of scan lines in the video image. Standard definition is 525 horizontal lines for NTSC and 625 lines for PAL.
Technically, anything that breaks the PAL barrier of 625 lines could be called high definition. The most common HD resolutions are 720p and 1080i lines.
35mm Resolution
There is an international study on this issue, called Image Resolution of 35mm Film in Theatrical Presentation. It was conducted by Hank Mahler (CBS, United States), Vittorio Baroncini (Fondazione Ugo Bordoni, Italy), and Mattieu Sintas (CST, France).
In the study, MTF measurements