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Frame load speed of digital video?
I now understand _most_ of the details about frame rates, interlaced and progressive etc.
However, I was watching a video describing the technique of getting to 24fps “to look like film”. Ironically the demo video itself looked quite flickery: more than I would like, and it was using 24fps progressive. I do not remember true film flickering as badly.
So I am wondering how fast the frame is filled from start to finish, in a progressive frame load. I would imagine that film shuts the shutter, moves the film, opens the shutter and so on. I reckon that could be done far faster than 1/24 second, so you get less flicker. If video actually takes 1/24 second to fill the frame, then of course you will get more flicker.
I have something of a bee in my bonnet regarding video flicker, as some of you may know 😉
So any input would be gratefully received.
EDIT: I looked for a more suitable forum area, but could not see one.
Nick
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7 Replies
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Yes you are correct:
Shutter speed on standard film is around 72hz.
24p and a shutter speed of 1/24 looks like crap! I too loath shutter flicker…
Personally I like 24p and 1/96… That make me happy.
As you play with shutter speed you will notice the slower the shutter the more light is allowed in, so many people slow it down to help reduce grain in dark environments… Just watch out for fast moving object and especially fast pans / whips…
President: http://www.VertexMedia.com
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Thanks for the reply. I take your points and it’s always a fight between ISO and noise and slow shutter.
But I was more wondering about the actual playback, and what causes flicker there. My camera can do 50p and it looks like silk. But if I convert to 25p, there is a noticeable flicker. That is in spite of all the help I have had here to optimise it and including turning off Vegas’s daft “smart resample”.
I still prefer interlaced for any action shots for its smoothness, although I realise it is not quite as good even at its best with still scenes, compared to progressive for detail.
Nick
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Ask 100 videographers to define “Film Look” and you’ll get 101 different replies. If you want a “film look”, shoot on film.
Steve Mann
MannMade Digital Video
http://www.mmdv.com -
Hey! Never got a heads-up from the forum about your reply. Sorry.
OK. Thanks. That pretty much confirms what I thought.The whole paradigm is just so different.It was just that people who at least _sounded_ good were going on about it. 🙂
Nick
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OK. I will just float this idea.
The reason I see objectionable flicker is that the previous frame is being gradually (in frame rate terms) replaced by the new one. So what the eye is watching is both frames gradually melding from one to the other. When I watch 25/30p with lots of action, it really does look as if the frame flickers back and forth, and not just as if it’s the flicker of the new frame (if you take my meaning). Film on the other hand would shutter the old frame, move it one and then open the new frame. the only flicker is shutter time: one single action.
Thoughts appreciated.
Nick
Nick
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Progressive frame display on a PC screen (or flatscreen TV) is basically instantaneous, and even faster than a film projector shutter opening. Frames are displayed complete, and there is normally no transition time between frames, no shutter blanking, nothing. Just one complete frame instantly replaced by the next complete frame 25 or 30 times per second.
You might be seeing the results of frame blending as part of a frame-rate change/mismatch or deinterlacing. That can create intermediate frames where you see the “ghost” of the previous frame blended with the current frame (or fields in the case of deinterlacing).
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Thanks very much for the reply.
That was the info I was looking for. I was not sure if the frame was built over the 1/25 second period, or was instant. hmmmm.. No this is not ghosting…… I think. I have seen ghosting , mostly when I do not switch off Vegas’s “resample”. Nearly all action or panning in Progressive stuff shows it at sub 50 fps frame rates, on TV, DVDs and on my own footage (and everybody else’s). I assume it’s there at 50fps as well, but just too fast to see. Well de-interlaced i clips do not show it.
Nick
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