Ultmately dumb question: What is 24f for?

[Evan Donn]

Originally Posted by Mats Frendahl

Jack, trying to sum it up:

Interlaced: More detail but "jerky"
24p/25p: More dreamier look

Is there any disadv. then of 25p regarding rapid movements of the "actor", i.e. will 25p have more difficulty of recording rapid movements?

With "jerky" - do you mean movement, i.e. that Interlaced are inferior of recording rapid movements?

Somehow things have become switched around in this discussion - 60i produces smoother motion, not jerkier, and (depending on the cameras in question) may have less detail than true progressive footage. With 60i you are trading off some vertical resolution (I believe it's approximately 30%) for greater temporal resolution - 60 samples per second versus 24.

Next time you're watching a movie (24p) in a theater and there's a shot panning along with a character or vehicle, try focusing on something other than the main subject - maybe the sides or corner of the screen. If you've never done this before you'll be blown away by how badly the image is stuttering there. Now try the same thing while watching a football game on a CRT television (60i) - no stutter, just smooth motion.

The higher temporal resolution of 60i more closely approximates what the human eye sees, and thus may appear more 'realistic', while the subtle stutter of 24p may tend to distance the viewer from the material a bit. I think the biggest difference though is one of conditioning - most viewers have a lifetime of associating the smooth motion of 60i with newscasts, sports, soap operas, reality shows and home videos. Likewise, the stutter of 24p is associated with movies and high production value dramatic television. This isn't necessarily a conscious awareness - most people wouldn't look at something and say 'that looks like 60i', but most can say 'that looks more like a movie' or 'that looks more like a home video'. 24p isn't a magic bullet in terms of making your video look a 'real movie' - but it's certainly an important piece in a puzzle that also includes lighting, staging, acting, sound, etc.

Originally Posted by Jack Walker

With progressive video the mind is simply blending the frames into continuous action. However, with interlaced video, the mind is getting frames where every other line is offset a little, and the mind has to first lineup the offset lines, then blend the frames into video.

Actually, this is not what's happening with interlaced video. Interlaced video isn't meant to be played back with the two fields displayed simultaneously with an offset from each other. On an interlaced display (a crt television) each field is displayed one after the other so the mind is basically seeing 60 discrete half resolution frames. If you're seeing offset lines and noise in 60i footage it's because you're watching interlaced video on a progressive display (i.e. an LCD or CRT computer monitor) and the playback software/hardware is incorrectly displaying the pairs of fields simultaneously - instead of either dropping one field, blending the fields together, or scaling each field to full frame and playing it as 60p.

[Jack Walker]

This is what I meant when I said the words mean different things to people.

The "jerkiness" I'm talking is not the strobing or studder of slower frame progressive display. I'm talking about what's happening within the picture. It's more noticeable to some than others. As one half resolultion frame is displayed after the other, with moving objects, perhaps an arm waving, each half resolution frame is offset from the previous.

Meanwhile, the mind is trying to put together a complete picture. In some people there is a "jerkiness" or "shimmer" (again a misleading term) or other distraction. Some people see it and some don't.

On a progressive display, the offset is easily seen since both half resolution frames are displayed at exactly the same time. However, it is still there even if the frames are displayed (normally) one after the next, but not as obvious. On a CRT, since the images remain a moment after they are put on the screen, in effect, both fields are appearing simultaneously, as well as non-matching fields are appearing together, as the second field of one frame and the first frame of the next are seen.

There is a difference in how different people see this. I'll refer once more to interlaced computer monitors. Some people aren't bothered, and others can barely used them.

I like Chris Hurd's answer the best,
sports: 60i
wedding: 30p
narrative: 24p

The 60i will give the most detail and smoother action because of the higher frame rate, though interlaced. 60p would probably be even better.

For the wedding, the 30p would take the edge off the reality show look of the wedding but still leave a little leeway to do video style camera work.

For the narrative the 24p would give the look people are used to and probably adds a bit of timelessness. However, rules for camera work are a bit stricter in some regard.

It all doesn't make much difference unless it is applied to actual video, so I will quit and go back to work.

[Greg Boston]

Originally Posted by Jack Walker

On a CRT, since the images remain a moment after they are put on the screen, in effect, both fields are appearing simultaneously, as well as non-matching fields are appearing together, as the second field of one frame and the first frame of the next are seen.

That's correct, the persistence of the phosphor on the CRT face helps create a full frame from two fields even though they aren't displayed simultaneously.

You keep mentioning interlaced computer monitors but virtually all computer monitors I'm aware of in this day and age are progressive.

To Mats: 24P came about as an acceptable trade-off between the illusion of continuous motion (more so in a darkened theater because the iris of our eyes opens up and creates 'persistence of vision'), and the higher cost of running film through the camera faster. To help with the 24P illusion, they have a mechanical shutter on the film camera that rotates and exposes each single frame twice, effectively doubling the frame rate. So each exposed frame has two instances of the image at 1/48th of a second differential. When projected back in a theater, the mechanical shutter on the projector flashes each frame twice on the screen so you effectively see 48 images per second, not 24.

With video cameras, the ability to shoot at 24 frames per second with a shutter of 1/48th helps create the same cadence and motion blur of film. But as has been stated by others, this is just one piece of the puzzle in making video look less like video and more like film. Adding gamma curves to video cameras that behave like film stock is another part of it.

Hope this helps,

-gb-

[Mats Frendahl]

Greg, OK - It's time for me to put theory into practise. Will be interesting to test 50i and 25p/25F for the next concert.

[Jack Walker]

Originally Posted by Greg Boston

You keep mentioning interlaced computer monitors but virtually all computer monitors I'm aware of in this day and age are progressive.

The only point was that they bother some people and not others... though the interlaced monitor doesn't really exist anymore.

Just as some find flourescent lights very uncomfortable and others don't.

I think there is a significant variation in the way people perceive some types of motion.

[Bo Sundvall]

Hi

Maybe a little off topic, but here is a link to a document describing the different modes, interlaced, frame and progressive. I'm not shure that the fram mode in XH-A1 is done as the document describes as Canon doesn't specify how their frame mode is done, but as there is a drop in resolution one can jump to conclusion that the frame mode in the A1 is done that way.

ftp://ftp.panasonic.com/pub/Panasoni...ressive-WP.pdf

A little note concerning film to PAL transfer. As there is so small difference between film, 24fps, and PAL, 25fps, the conversation is done by just speeding upp the film to 25fps. That's why films allways are 4% shorter in length in PAL countries. The small difference in audio pitch is not noticeable.


Regards,

/Bo

[Blake Calhoun]

One thing I haven't seen mentioned in this thread is the advantage that shooting in progressive mode (24, 25, 30, etc.) means for VFX work. Much easier to work with progressive footage for most VFX jobs.

[Ken Wozniak]

I just shot my latest wedding in 24F, and I think it looks spectacular. I wanted to go with 30F, but the lighting in the church was so bad that I needed 24F to keep gain down to 6db while still getting a usable picture.

I'm one of those people who is bothered by interlaced monitors (especially when people leave them set to 60 Hz) and fluorescent lights, so the frame rate of video is readily noticeable to me.

My B roll for the wedding was shot in 60i and had to be converted to "almost" match up with the 24F footage. Color aside, the 60i footage has that "live, you-are-there" look to it, while the 24F footage emulates the feel of film and gives the client something that "Uncle Bob's" camcorder can't give them. Plus, stills grabbed from 24F are MUCH better. 24F provides a more intimate look, which is ideal for a wedding video.

I suppose SFX work in frame mode would be easier as well, but I haven't had time to "play" with the A1 yet. I thought I'd get the chance with the DV Challenge, but I'm a bonehead and missed the posting of the theme.

[Mats Frendahl]

I made some tests (connecting the A1 to a plasma via component) on 25F compared to 50i. Paning in 25F cause a "studdering" or "strobing" effect on the background. 50i is smooth as you would see it with your own eyes. Is this smooth movement what some refer to "video-ish" and the more jagged as "film-ish". With this small test I must say that 50i is superior, but it is *not* a complete test so I might reconsider when tested more.

[Jack Walker]

Originally Posted by Mats Frendahl

I made some tests (connecting the A1 to a plasma via component) on 25F compared to 50i. Paning in 25F cause a "studdering" or "strobing" effect on the background. 50i is smooth as you would see it with your own eyes. Is this smooth movement what some refer to "video-ish" and the more jagged as "film-ish". With this small test I must say that 50i is superior, but it is *not* a complete test so I might reconsider when tested more.

I suggest you set the camera up, don't move it, then sit in front of it, walk around in front of it, jump up and down, skip rope and run by it. You will see more the differences this way.

Fast panning is not something done with 24p, and it will show the strobing effect. With 24p/25p you want to follow an object when panning to hide the background strobing. The short DOF in film also helps to hide this.

However, movements inside the frame look fine, but different with 24p than interlaced video.

Another comparison you could make would be the stage sequences in the Altman film The Company -- compare these with a broadcast stage presentation of a ballet or dance performance. The lighting is still different, but similar enough to compare the motion. The Company was shot with progressive video and transferred to film.

An excellent example of how video looks is the Korean soap operas. (Perhaps in Europe you have the Mexican soaps.)

[Mats Frendahl]

Jack, using 25F/50i how would you estimate the fast moving hands of a pianist to be? I assume - not tested yet - that the 50i might have the interlace artifact. In this (pianist) case the background does not move at all, but the hands in the center of the image move all the time, and alot, and quick.

[Greg Boston]

Mats, you are learning why using 24/25P demands special camera techniques. If you want to shoot this way, you have to approach it more like a film camera operator would. Learn those techniques, and you'll be well on your way to understanding what does and doesn't work.

Also, remember what I said about a darkened theater? Too many people these days try to watch 24P in a bright room and it looks more strobe like. Review your 25P in a darkened room after your eyes adjust and see if it looks better. And, when you shoot 25p, don't use 1/25 shutter speed... double it to 1/50 just as 24P uses 1/48th.

Have fun and keep learning!

-gb-

[Jack Walker]

Originally Posted by Mats Frendahl

Jack, using 25F/50i how would you estimate the fast moving hands of a pianist to be? I assume - not tested yet - that the 50i might have the interlace artifact. In this (pianist) case the background does not move at all, but the hands in the center of the image move all the time, and alot, and quick.

Interlaced video (50i) will look fine when viewed on a TV. Viewed on a progressive computer display, you will see the interlace lines.

Practically speaking, fast actions can be captured well with both 24p/25p progressive and 50i/60i. The difference for the operator is in the types of camera work that can be done.

For the viewer, if the camera operator does his job properly, the viewer will see what can only be described as somewhat vague and philosophical differences in the quality of the motion and the emotional experience (together with the lighting and other aspects of the video) the video evokes.

Taling too much about something quickly becomes an excuse for not doing something.

[Mikko Lopponen]

Originally Posted by Mats Frendahl

Going from 30 fps to 24 fps might be noticed, but I cannot pin-point the difference in 50i and 25F. Perhaps I simply don't look in the correct places..

You serious? The difference is huge!

[Piotr Wozniacki]

Originally Posted by Greg Boston

24P came about as an acceptable trade-off between the illusion of continuous motion (more so in a darkened theater because the iris of our eyes opens up and creates 'persistence of vision'), and the higher cost of running film through the camera faster. To help with the 24P illusion, they have a mechanical shutter on the film camera that rotates and exposes each single frame twice, effectively doubling the frame rate. So each exposed frame has two instances of the image at 1/48th of a second differential. When projected back in a theater, the mechanical shutter on the projector flashes each frame twice on the screen so you .

With video cameras, the ability to shoot at 24 frames per second with a shutter of 1/48th helps create the same cadence and motion blur of film. But as has been stated by others, this is just one piece of the puzzle in making video look less like video and more like film. Adding gamma curves to video cameras that behave like film stock is another part of it.

Hope this helps,

-gb-

Greg, while I agree in general with your points, I believe it's not necessary to use the 1/48th shutter speed in order to "effectively see 48 images per second, not 24". You can achieve the same when watching each frame more that once; the modern plasmas do it by displaying the 25p (PAL) material with refresh rate being a multiple of 25, e.e. 50 or 100 Hz. Also, some can sense the 24fps candence and swith the refresh rate to its multiple, like 72 Hz (the Kuro line by Pionner) or even as high as 120 Hz.

This lets you avoid flicker while staying synchronized with the actual fps.

The stiff rule of shooting only with 1/48th (1/50 for PAL) deprives the 24/25p mode user of a very nice bonus of the 1/24 (1/25th in PAL) shutter speed: a full stop more exposure, so important in those HDV camera in low light situations!

With my V1E, I almost exclusively use 25p with 1/25th for church events (not just weddings, but also music performances etc). This lets me stay safely below the 9dB gain needed in those notoriously dim surroundings (anything higher than 9dB is unacceptable for the V1e's progressive mode). I'm very satisfied with the picture I'm getting (of course, there is not much movement involved, which helps in keeping the 25fps stutter- and blur- free a lot).