Cineframe 24/Cineform 24p cadence
 

I was thinking about the cadence of Cineframe 24 footage and how it is not exactly 24 evenly spaced frames per second. Then I realized that 24p with a 3:2 pulldown isn't exactly 24 evenly spaced frames per second either, and nobody has ever complained about that. Then I was thinking that 24P which originated from CF24 might actually be a closer match to the timing of interlaced playback of 24p footage and maybe the timing discrepancies I think I'm seeing aren't really that big a deal after all. The timing on the regular TVs that most of us still use might even be better than true 24p. Is this the case or am missing something?

That the two temporal discrepencies might actually cancel out?? Looking at 24CF, that doesn't happen, but I should put pen to paper and try and figure out how it could be done.... (if possible)

Graeme

Well I may be missing something, but it seems like on interlaced pulldown playback about 50/50 odds that it would either cancel or double itself.

Well, with 3:2 pulldown, it's three fields and two fields. If either of those three or two fields line up with a corresponding field from the 60i, then that's the best you'll get, given 3:2. However you can generate those 24p frames from info from more than 1 field, and that's what CF24 doesn't do!

Graeme

It all depends on how your display deals with the pull-down.

Some video systems can decode the 2:3 pull-down in real time. True interlaced displays simply display it directly from the disc. Some progressive displays convert the 24 frames per second into 60 progressive frames, and display 2 and 3 and then 2 and 3 again to fill up the 60 Hz refresh rate. Some other displays refresh at 72 Hz, resulting in the 24 frames each being played 3 times.

Early tests indicated that it's very hard to differentiate CF24 and true 24P played side be side... Once this was accomplished viewers noted it was difficult to determine which was actually better.

Much of the "strobing" people report with respect to CF24 is just typical 24 Hz strobing and poor shooting for the low refresh rate (pans too fast, poor cinematography etc.). This is excacerbated by the fact that you can't lower the shutter speed past 1/60 s. If the shutter could go to 1/48 or 1/24, it would be much less noticable.

That isn't to say the CF24 cadence is ideal, or that the variable resolution of CF24 depnding on which field was sampled is good... but in real world terms, CF24 isn't that bad.

-Steve