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Old June 24th, 2004, 07:49 AM   #1
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Frame Rate Q

Newbie question here:

How is it that the human eye (at lease mine) can't see the frames flipping at 24fps when watching a "Hollywood" movie? I know that if I play a game on my G5 and I only get 24fps it will be obvious! Is it because DV does better at putting the frames together?
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Old June 24th, 2004, 10:25 AM   #2
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The simple answer is film is shot at 24fps, but projected at 48fps (frames are doubled) so you don't see jitter etc. The video game is showing 24fps and you see the lack of smoothness.
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Old June 24th, 2004, 10:30 AM   #3
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Jeff,
True enough, and in fact, depending on the projector, 24 frames per second is projected at 72 images per second. With a three bladed shutter, each frame is "flashed" three times.
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Old June 24th, 2004, 06:43 PM   #4
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Really?

I thought when I saw a movie in the theater I saw it at 24fps...I didn't know that a 'shutter' flashes the frame three times on-screen. When did they start doing that?

You are still only seeing 24 fps...not 48. It is the same frame, just flashed a couple times. Just like TV is 30fps (29.97 if you want to get technical about it), and not 60 fps.

I think that you are used to the smoothness of the game...it flows more like real life...where the film work seems dreamy when presented 24fps.
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Old June 24th, 2004, 07:58 PM   #5
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Film is usually shot so that there is lots of motion blur. This helps your brain perceive motion. Games do not have motion blur.

2- Your brain sees more "frames per second" when the image is changing quickly. In a CRT, there is an electron beam that scans across the monitor line by line many times a second. This is quickly changing motion that your brain perceives differently.

I'm not very good at explaining this, but try setting your CRT to a refresh rate of 60hz. You will probably notice a little eye strain looking at your monitor.

3- "Is it because DV does better at putting the frames together?" DV stands for Digital Video, which refers to the video format on mini-DV tape. I assume you mean the video you see on your computer monitor.

4- "Just like TV is 30fps (29.97 if you want to get technical about it), and not 60 fps."
TV is 60 (59.94) fields a second. That makes a difference to the way motion looks on a television compared to 30fps progressive.
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Old June 24th, 2004, 08:17 PM   #6
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<<<-- Originally posted by Glenn Chan : DV stands for Digital Video, which refers to the video format on mini-DV tape. I assume you mean the video you see on your computer monitor. -->>>

Whoops. I meant digital video or film as opposed to a playing game on a computer monitor. I thought I read somewhere that certain video camera's "guess" what is happening to make the frames smoother...

So if DV is only MiniDV what would you call the latest Star Wars episodes? Aren't they completely digital?
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Old June 25th, 2004, 03:22 PM   #7
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Bluring and frame rates

<<<-- Originally posted by Glenn Chan : Film is usually shot so that there is lots of motion blur. This helps your brain perceive motion. Games do not have motion blur.


Ouch!

I keep everything I or the director want in focus, in focus, and everything I/he wants out, out, period.

The motion blur is induced by the "normal" motion picture camera speed of 1/50 sec shutter at 24 fps, not (we hope) intentionally :)

24 fps was originally chosen as the slowest frame rate (for film economy) that could be used without the human eye registering a frame change (an improvement over the early 18 fps films).

Unless it's a special effect -- film shot at 24 fps through the CAMERA gate travels through the PROJECTOR gate at the same 24 fps, otherwise the original action and the projected action would differ.

Depending on the number of blades a projector shutter has (at least two, most now have three, but there are four bladed projectors as well), each frame is viewed by the audience two, three, or four times (at 1/48, 1/72, 1/96 sec. intervals) which is above the human eye's theoretical "persistence of vision" of 1/17 sec.

TV sets and computer monitors (this is the DV tie in part ;) use the same principal (the projection "shutter" is the refresh or scan rate). The higher the scan rate (or number of times it is scanned) the smoother and more fluid the action or movement.

This is just a simple nuts and bolts explanation to a very complex subject that could probably have a message board all its own.

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Old June 26th, 2004, 01:45 AM   #8
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Quote:
Whoops. I meant digital video or film as opposed to a playing game on a computer monitor. [...]

So if DV is only MiniDV what would you call the latest Star Wars episodes? Aren't they completely digital?
DV stands for Digital Video and is one of the many digital video formats. Does that make sense?

Star Wars was shot on HD or some better format- I forget which. HD is also a digital video format (in the sense that HD is a subset of digital and video).

Quote:
I thought I read somewhere that certain video camera's "guess" what is happening to make the frames smoother...
I am not aware of any cameras that do this. There are some plug-ins that are designed to slow down video footage. They guess at what the in-between frames look like.

There's also mini-DV cameras that shoot 24fps progressive. They don't guess anything though.
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