Tell Me about Progressive

Progressive scanning does not cause motion judder, image repetition does.

Interlaced scanning produces 50 images per second, but each image has only half the lines and thus only half the vertical information. Progressive scanning produces all the information in each image, but, if the capture rate is 25 frames/second, then each image has to be repeated for showing to avoid unacceptable brightness flicker. Progressive scanning does not have to be at 25 fps, the Panasonic Varicam runs at up to 60 fps, so produces very smooth motion with no flicker and no judder. Most of the electronic film cameras will also run fast like this, but "film"-makers want the effect of the judder, they specifically want it, so we have to provide it.

I regularly set cameras for HD shoots, and at least 95% of them want a film-look shoot with jerky motion, so the cameras run at 25fps. I can't help it, that's what they want.

All films are shot at 24 fps, but shown with frame repetition to daise the flicker frequency to 48Hz. They use a shutter in the projector to do this when real film's projected. When shot electronically, the frames are repeated. Very many films have been shot this way, several thousand at the last count.

If you want to shoot film-style, you have to accept film rules, there are lots and it's not obvious what you have to do. But, I get significant money from training people in doing this. And I still get paid for producing the camera setups, the HDX400 retest for example.

If you go and read White Paper 53, you'll see lots about this, but number 8 might be useful as well.

Alan

I appreciate your technical overview. I know you haven't seen the footage but the shot of vehicles travelling at normal speed albeit in a skipping motion with considerable blur is not something I'm familiar with. Are we saying that a film and video camera in progresssive mode will produce identical judder artifacts if both sources end up on tape?

Did George Lucas have this problem or maybe he shot interlaced.-where are you George?

Pete

You sit in the cinema and you're shown 24 different still images per second, but you're shown each frame twice, to up the flicker rate to an acceptable (though barely minimal)48Hz as Alan says. (Super-8 frames are shown 3 times before pull-down and that was deemed acceptable as the flicker is then 54 Hz).

If you pay a fiver for the cinema ticket you're paying £2.50 to sit staring at an unlit screen, in almost total darkness with only the exit lights over the door to entertain you, but I digress.

Our video cameras shoot 50 different pictures per second (ok, there's fields and frames to go into here) and we've all got pretty used to the smoothness that this imparts. So video film makers have resorted to shooting progressive scan in an attempt to emulate film's staccato look. Their thinking is correct but often their projection isn't. A CRT will still show their footage as interlaced and they'll still have a 50 Hz flicker.

NTSC shooters seem to be a lot more hung up on the 'film look' than we PAL users are, and my guess is that their 30 fps 60 Hz video is further from the cinema's 24 fps than our 25 fps is.

So I'm with you Pete. The film look came about through cost reasons and persistance of vision reasons, nothing else. We've now managed to make our motion pictures a lot smoother and what happens? Nurds miss the cinema stutterand flicker and have tried to degrade their camcorders to hark back to the old days.

Spielberg BTW uses a lot of very high shutter speeds in his Ryan, Brothers, etc footage, and this inevitably leads to loss of information. Whereas the video camera records everything in front of it, the film camera records less than half.

tom.

Thanks Tom

I did view your comments elsewhere about not shooting progressive on a pd150(I didn't think 150/170's wre progressive aprt from still mode).

All I'm saying is that the staccato pictures I was shown on a plasma from a progressive scan DV camera do not equate to the pictures I'm used to viewing either in a cinema or on tv bearing in mind that most tv commercials are still generally shot in 35mm.

So is anyone on this forum shooting in progressive as a matter of course?

Pete

I think there are two reasons for - valid technical ones, and historic arty ones. The first set have a lot to commend them (try the EBU, http://www.ebu.ch/en/technical/trev/trev_home.html and look for articles about "HDTV in Europe" and then the progressive approach, maybe article 300?). The second set have much less, though I'll go along with them to some extent.

As has been said above, there is progressive scanning and progressive scanning. It can be either 25 or 50 full frames per second. Obviously the latter will not give the jerkiness that the former does, but that seems to be precisely what appeals to people who want "the film look".

Over here a big objection to the JVC HD100 has been that it will only record 25p to tape. In the States they complain that 24p is not an option on other gear. Sometimes I feel sorry for manufacturers......

If it is considered that the main market for a film may be eventual transfer to film, 24p makes much sense - 24 individual, discrete images per second.

Finally, I believe that some cameras aren't true progressive anyway. They give "the look", but without gaining the true benefits. But now I'm getting out of my depth.......

I've always suspected that there is something else going on here but I do accept all the theory that has been quoted in these forums

I suppose what I'm saying is that what I and my dealer saw on that plasma is not what I regard as a film look in terms of judder. To my eye film does not have that excessive judder. If it did then it would be considered unacceptable particulary by purists. The dealer was worried that the camera may be returned by buyers finding the judder unacceptable since there seems to ne no way of eradicating it once it's on tape.

Pete

The film look came about simply because the early film makers decided that they could 'get away with' only shooting 24 different pictures per second. Although this gave a somewhat jerky approximation of the original scene, it was acceptable to viewers, and it stuck. 8 mm film reduced this to 16 fps, but this was really to save money at the expense of smoothness.

Of course they could've made their films look smoother if they'd shot more frames per second, but they would've needed more light at the time of shooting, and more money to buy more negative film stock. Film speed was an oxymoron, remember.

The same historical lessons hold true with our current video system of course. In the early days of TV bandwidth availability insisted that half resolution interlaced fields were generated and transmitted. This is certainly not ideal, and progressive scan (PS) is a far nicer ideal that modern technology has allowed to progress. But of course we're (generally) still using display screens that show interlaced footage, with all the losses and compromiss this brings.

I think the jerkiness you're seeing Pete is the result of intermixing standards. It's fine if you shoot 25 different full resolution pictures per second and show the same on replay, with allowances made for screen flicker. I know my Sony camcorders give better resolution in the PS mode rather than the nornmal interlaced mode, but the judder is quite unacceptable, so the 'normal' shooting mode wins hands down.

tom.

Which camera was it? The TRV900, for example, only records 12.5fps in progressive scan mode... I'm always amused when I read a post by someone who's just used one to shoot a movie in progressive scan for the 'film look'.

I'm with Unicorn - what camera was it? "Progressive" can mean so many different things, and the EBU wouldn't favour 720p/50 over 1080i/25 if it was necessarily always as you say! The JVC HD100 is 25p to tape, but when I actually saw the output I wasn't too put off. I suspect what you saw wasn't either of these cases, and "progressive" on it had more to with marketing than technology.

True 50p progressive is generally considered a good thing. 1080p/50 is generally considered the ultimate goal, for acquisition at least. Even at the top end, it's currently stretching available technology.

I'm sure you will understand if I don't mention a model as I don't want to alienate camera manufacturers. It certainly wasn't the Sony mentioned but is a semi-pro camera.

Anyway my comments are more about progressive in general in that the jerky pictures I see on playback do not bear any relation to the generallly smooth pictures on film. People talk about film operators framing shots to allow for movement problems. As someone that's been around film for along time in various guises that's not my experience.
As stated before George Lucas I'm sure wouldn't put up with the staccato movements I was seeing and yet we are told this is how film is shot. It may be shot that way but it doesn't look that way so why the difference? The smooth car shots in say 'midsomer murders' (film) look vastly superior to the similar shots I was seeing off tape

Thanks for your inputs

Pete

Pete, read my papers, it's all explained there.

Film doesn't give smooth motion, it's jerky, always. Film-makers (the good ones anyway) always avoid the range of camera speeds that produces jerky motion. Inexperienced users of electronic cameras in progressive mode rarely do, because they don't know what they're doing. They need training. That's what I do.

Then maybe you could run a workshop and train us all :)

Alans right - I'm sure there are recommended maximum panning speeds for different focal length lenses etc, all to avoid excessive jerkiness. Even so, I'm surprised the problem seems as severe as you make out.

Just two more thoughts. First is to wonder if a shutter has been switched in, as well as the camera being in progressive. I'd then expect the result to be a series of pin sharp images even when panning etc, and the "judder" effect to be worse. Second is to mention that getting field order reversed can give a truly horrible effect on motion - but I assume you're looking at a rushes tape, so wouldn't expect that to be the case.

I assume you are talking about 25p? 50p shouldn't give any problems. I can only assume when you talk of a semipro camera that we are talking of true progressive, and not some artifical effect.

I guess we need a break why I try and digest Alan's papers so I will bow out with one final question. In the meantime I will try and get more details and possibly a dupe of the offending tape. I like the suggestion about the shutter being set to another speed.

Is there currently anything being transmitted that was shot progressive that you know about or for that matter a film that I could rent.

thanks for your responses

Pete

1. Alan could you direct me to your papers? Are they the White Paper you were talking about?

2. HD100 only prints 25fps? I always thought it could record 24fps, what’s up there?

3. I'm not at all as technical as hope to be but surely George Lucas will be using a real real expensive camera compared to the smaller camera us mortals will be used to, and surely that’s why his footage looks as good as it does?!?!

4.

I agree, just spill the beanz - what camera was it so we could all be put out of our mysery!!:mad:
We could all do with knowing as much info as we can get :D

In the thread about HDTV and the BBC, when asked about what standard the BBC would use, Alan replied "Given that virtually all that has been shot in HD for the Beeb for several years has been 1080psf/25, I'd say it would be very silly to transmit 720p/50."

Since the BBC press release says that "Current series Bleak House and Rome have been made in HDTV,......", they would seem to be two examples for you, but to be honest I can't see any reason why proper 25p HD should look any worse than a feature film shot on real celluloid film from a judder point of view. So what you saw shouldn't look any different from the vast majority of films you rent.

Though a visit to a cinema last year, after a visit to IBC, made me feel that film folk should perhaps be after"the HDTV look", rather than TV folk being after "the film look"! ;)

If you want to PM me the details of the camera concerned, I promise not to tell..........

Agreed that Bleak House looks superb as does Star Wars but what I saw off rushes does look inferior so why the difference. Played about today with a different model of the same camera and a different dealer who agreed that pictures in progressive scan (displayed on CRT) were objectionable for reasons of judder. (720/25)

what happens between those juddery rushes and the output as per bleak house.

This wasn't the camera concerned but has anyone used the Panasonic DVX 100 in progressive mode(25fps) and achieved the same judder free result as bleak house / Rome(ignoring of course the other factors of compression, prime lenses etc.etc)

If you have then maybe it's me!

My head hurts and I haven't even started reading Alan's white papers yet.

Pete

Where can I find this WhitePaper?

start here : http://www.bbc.co.uk/rd/pubs/whp/whp053.shtml

The DVX100A does indeed do very much smoother progressive scan (PS) than the PD150/170, say. The latter switches to 12.5 fps in PS, which - even with the default 1/50th shutter speed is unwatchable it's so jerky. But then it was never meant for movies, whereas the Panasonic was marketed to capture the boys that wanted the 'film look'. It shoots 25 fps in PS mode, and these images are converted into 50 field interlaced for storage to tape and output down firewire.

It's still not as smooth as genuine 50i of course, and switching to this mode disables all sorts of camera facilities. But that's what a whole host of filmmakers seem to want.

tom.

Tom

I never realised that the 150/170 was a PS camera so I live and learn - thanks

Re the DVX100 I've noticed that the images looky jerky in the viewfinder. When they are outputed does that improve?

BTW have read Alan's white paper and although I skirted around the maths I found it extremely interesting. I'm wondering whether the problem I'm seeing is due to a shutter being set too high resulting in sharp edges. I will investigate furher for my own piece of mind and interest.

I'd love to see a workshop arranged (with Alan) whereby we could have these cameras lined up maybe with a NLE and take the whole process through to finishing to see the differences between say a semi-pro mini DV camera and a high end HD.

Pete

No. Camcorders have wysiwyg viewfinders. You're viewing at taking aperture, shutter speed, white balance and so on. The only difference is that generally the v'finder is an LCD, and a CRT display will indeed look somewhat different. The DVX should look perfectly normal in the 50i mode though.

High shutter speeds are very evident in the battle scenes in Gladiator, Saving Ryan and so on. Although you're still seeing 24 different frames every second, the total time the camera shutter is open in that second may only be 1/10th of a second, so huge amounts of info (that happened in front of the camera) fail to get recorded. This gives it that crisp, statacco look, but fast action is unnaturally 'frozen' somewhat like a stobe flash.

Our video cameras (when set to the default 1/50th sec shutter speed) record everything that happens - i.e. the shutter is open for very nearly the whole second. This gives the smoothing motio blur that looks a lot more like real life.

tom.

Tom, the vfs are almost wysiwyg but not quite. If the viewfinder had full resolution and were a sensible size (7" or more, studio/ob camera size) then you'd be right. But the vfs on small cameras are all under-specified, typically 50% or so, so a 1920x1080 camera may well have a vf that resolves only 960x540. Since you're expected to use this for focusing, they add some detail enhancement in the vf, so you can see the zingy edges. The problem is that this enhancement is at mid-low frequencies, so it looks awful. That's why vfs judder more than final outputs do.

I use this argument on HD shoots, to warn DoPs that the motion in the vf is going to look horrid, but that's what they're inflicting on the viewer, so be careful. As a result, the newbies all use camera motion sinsibly, and you get pictures that look like "Bleak House", stunning.

In practice, film people know about judder and control camera motion accordingly. Fast motion is fine (it blurs), slow motion is ok (it just looks a little restless), but motion at about 3 seconds/picture width causes the most problems with film and properly set HD cameras. My setting of the detail enhancement in HD cameras is intended to mimic the resolution and dynamic performance of real film, which it does by lowering the mtf in the mid range while sustainging it at high frequencies, so pictures look sharp when the stand still but lose quite a bit when they move, which is exactly what you get with all film stocks.

Sadly, you can't do this with many cameras, only with top-end stuff. So, even the DVX100 has mtf that's too high in the mid-range for a good film look, so you have to use it as though it were a 35mm move camera, slow pans (5 sec/pw fastest) are about the limit, any quicker than that and you get bad judder, but quicker than 1.5 sec/pw and yuou get blure, which is fine.

You just have to know what you're doing, that's all. There's no magic to it.

So when they ask you what shutter speed they should use, I hope you reply, "Thirty five years and a fiftieth of a second". I do.

tom.