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What is the difference between monitoring a progressive project as interlaced, compared to monitoring the same progressive project as PsF?
It confuses me both because of the actual different effects that sometimes occur when switching from one to the other, and in addition to that, the fact that there even exists the two options rather than just one.
The way I understand it:
Progressive material shot at 25 progressive frames per second that is displayed using monitoring equipment generating an interlaced signal of 50 interlaced fields per second, should look indistinguishable from progressive material because each field is from the same moment in time making it an effective image update rate of 25 frames per second.
That theory seems to hold, except, where it starts to fall down is
A: There exists a separate option and a standard called Progressive Segmented Frame, for which every definition I’ve been able to find describes something almost exactly as I’ve written above, with the exception that it has a name ‘PsF’ rather than simply described in a sentence as ‘Progressive material viewed on interlaced equipment’
B: On certain monitors, image artifacts such as moire and hard stepping on diagonal lines are readily apparent and a potential tech-check failure level problem when monitoring a progressive project is set to 50i, yet that same footage when viewed at progressive or at PsF looks fine.
I can kinda-sorta get why progressive viewed as interlaced might differ from progressive viewed as progressive, because even though the image update rate is the same, there is still at least half the lines not visible at any given 50th of a second and perhaps for certain finely detailed material (usually drone footage scaled down from 4K to HD) the persistence of vision effect doesn’t work as smoothly as a progressive scan and causes some kind of issue (I don’t really know I’m reaching), but I can’t figure out why on earth there’d be a visible difference between progressive material viewed at PsF and that same material viewed at interlaced.
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1 Reply
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You just about covered it. Content flagged as PSF can be treated by a display device capable of progressive display as progressive. Its carried in fields for compatability with interlaced systems. Which is why PSF exists.
Progressive content as interlaced not flagged as PSF won’t be handled as progressive by displays that can handle progressive display and indeed you will suffer interference between field updates.Pat Horridge
Broadcast & Post Consultant, Trainer, Avid Certified Instructor
Free online Tutorials at VET digital media academy online https://vimeo.com/channels/752951
pat@vet.co.uk
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