18 or 24fps?

[mcflytrap]

What are the benefits of shooting at 24fps as opposed to 18fps? Is there a big difference?

Thanks a lot...
-mcfly-

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[MovieStuff]

Well, if you want to transfer to video on anything other than a Goko unit, then 24fps is going to give you smoother motion characteristics. The rotating prism of the Goko makes transferring at any speed possible but the sacrifice is sharpness. In addition, the Goko units seem to work best with older tube style cameras, which don't offer the best picture quality compared to modern chip cameras.

If you shoot at 24fps, your project will be following the standard for motion picture production the world over and will allow you to do other things like blow up to 16mm. In all, I'd say that it depends on what you want to do with your final footage. If you are going to just look at it on your projector at home, then 18fps is economical and looks just fine. It also lets you shoot with 25% less light! However, if you want to do anything else like transfer to video or blow up to 16mm, then shooting at 24fps is best.

Roger

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Roger Evans
MovieStuff
http://www.afterimagephoto.tv/moviestuff.html

[Nigel]

Shoot 24fps! I would like to expand but it seems to be covered. Simply put it is the best way to go.

Good Luck

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[Mr Blackstock]

As i understood from an earlier posting, transfering 18fps footage to video would be fine if one used "pal"?

The person suggested that in australasia this was common. Would it be an economical alternative to those in the northern hemisphere?

Or am i so way off that i need the world of transfer explained.....again.

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[MovieStuff]

<BLOCKQUOTE><font size="1" face="Courier, Arial">quote:</font><HR>Originally posted by Mr Blackstock:
As i understood from an earlier posting, transfering 18fps footage to video would be fine if one used "pal"?
Or am i so way off that i need the world of transfer explained.....again.
<HR></BLOCKQUOTE>

Hi, Mr. Blackstock!

Well, in a nut shell, trasfers of 18fps footage to PAL do work better than transfers of 18fs footage to NTSC. Here is why:

To start with, don't think of PAL as 25fps. Think of it as 24fps for the sake of this discussion. The reason is that the speed difference it so minimal that no one can tell. Also, realize that any camera that shoots at 18fps is just as likely to shoot at 19fps or 17fps. There are no crystal synched 18fps cameras that I am aware of. Therefore, playback speed is relative ONLY to what looks good to the eye and not a mathmatical absolute.

Now, when 24fps film is transferred professionaly to NTSC video , every fourth frame is doubled to artificially create 6 additional frames per second. That stretches one second of film (24 frames) out to one second of video (30 frames). This works because 24+6=30 and also because the 6 additional frames are evenly spread across the 24. Unfortunately, there is no mathmatical way to do that evenly with footage shot at 18fps for transfer to NTSC video.

For PAL, things are more convenient. If you simply double every third frame, then 18fps footage can be stretched out to 24fps easily. Again, because the extra frames are distributed equaly across the entire 24 frames, it smoothes out the motion. Now, because PAL actually plays back at 25 and not 24, the motion will be a hair faster but not enough to notice.

Shooting at 24fps is still going to be the best, since each frame of film can simply be transferred to a frame of PAL video with no frame doubling of any kind. But 18fps footage will work on PAL in the same way that 24fps footage works on NTSC, though not as smooth.

Roger

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Roger Evans
MovieStuff
http://www.afterimagephoto.tv/moviestuff.html

[mattias]

yeah, a three bladed shutter (standard) and 16.67 fps gives you a perfectly flicker free pal transfer without any noticable speed change. i think it strobes too much when there is fast motion though. i never use it if i'm transferring to video, but i always shoot 18 fps if i'm "only" going to project it...

/matt

[Mr Blackstock]

Now i get it,

For now i will stick to 18fps, and very fresh batteries! very clear explaination, thanks.



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[#Pedro]

In the past, I always used 18fps as a standard, for economy reasons. Then I made a 24fps test and I thought is astonishing better: All is much smoother (camera movements, object movements, picture stableness) and looks more powerful and professional. Less shutter effect. The sharpness gets increased notable, as it depends on the framerate. Magnetic sound quality is better, too, meet HIFI requirements.
Pedro

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[rewolff]

[QUOTE] Unfortunately, there is no mathmatical way to do that evenly with footage shot at 18fps for transfer to NTSC video.[QUOTE]

I've grabbed video at 25 FPS, and played it down to about a third of that speed. To my surprise: this plays really smooth.

What I did was to just play the frame closest to the time that my reduced-speed timeline was progressing.

In fact, that's just what you're doing if you're duplicating every 3rd or 4th frame for upscaling 24 or 18 to 30 or 24.

My guess is that someone has tried this, but it didn't look good? If that's the case, then you might need a bit more trickery, which may not be easy if you're not doing things digitally.

fn_18 = 18 * t .

Is the formula for the frame number at 18 fps (fn_18).

To convert this footage to 24 fps, you'd have:

frame_24 (fn_24) = frame_18 (fn_24 / 24*18)

(for simplicity, lets just round down).
to check that this is equivalent to "duplicate every third frame", frame 0 and 1 both are duplicates of frame_18(0), just like frame 4 and 5 map to frame_18(3) of the original.

OK. Now for 18->30 conversion we'd get:

frame_30 (fn_30) = frame_18 (fn_30 / 30*18)

This will space the frames as evenly as they go.

You could also interpolate between adjacent frames:

frame_30 (fn_30) = (1-q) * frame_18 (fn_30 / 30*18)
+ q * frame_18 (fn_30 / 30*18 + 1)

where q = p is the fractional part of: fn_30 / 30*18 .

but as you almost never have an original frame, you'll blur the original, leading to fuzzy result.

I expect the best results to be achieved with the interpolation only kicking in when we're right in the middle between two frames.

So:

q = 0 for p < 0.4
q = p for 0.4 < p < 0.6
q = 1 for p > 0.6

Has anybody tried this? Should I patent it?

Roger.



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[mattias]

> Has anybody tried this?

sorry to rain on your parade, but what do you think?

/matt