What's the effect of pulldown?

[Tim Sills]

Hi All,

Using the search option it is clear that many people have discussed pulldown and how to do it but I am finding it difficult to arrive at a simple answer:

I have the PAL version of the HV20 so I have 25p or 50i. If I use 25p the imagery appears "stuttery" for the lack of a better word, whether viewed on a PC screen or TV. No such problem with 50i. Will pulldown remove this effect and make my 25p imagery appear smooth?

Also, given that the HV20 can be switched into a progressive mode in hardware, what's all this business of extracting progressive data from an interlaced stream? Isn't it natural to expect that 25p data is actually exported using firewire or whatever as a 25p data stream?

When I record something in 25p, import into Movie Studio Platinum 8 and tell it that it's custom (progressive) footage, nothing complains and I end up with my rendered result, also stuttery mind you...

Umm, little help please guys.

[Enea Lanzarone]

The whole pulldown thing is a pure NTSC issue, where the HV20 has a 24P mode (with pulldown), not a 25P (no pulldown) as the PAL model. The idea of removing pulldown is to get 24 full and individual frames to edit instead of the 24 frames stored in a 29.97 container. In your 25P footage there's no pulldown to remove. If you consider 25P "stuttery"...well, that's how it looks. It's half the time information of 50i, so it will never look as smooth. Some people hate it and some love it. To me, for example, 50i looks too real and way too smooth, so I always shoot 25P, which I don't find to be stuttery at all (tastes are different). The only thing you can do to keep motion as smooth as possible even in 25P is to keep the shutter not higher than 1/50 and panning a little slower than usual.

[Paul V Doherty]

I would like to add my $0.02 on the issue of 24p/25p and "stutter":

24p/25p is superior for narrative story telling and the impartation of higher production values.
Interlaced video is 80 year-old technology and ought to be confined to the 20th Century. ALL modern video displays are progressive by nature... that is not going to change.

Interlaced is rubbish. Interlaced looks cheap and nasty. Interlaced says "I'm a cheap video production and/or news/sports/reality event"
Progressive says "I have higher production values. I'm telling you a narrative story. Disengage your doubts and enter the fantasy world I am depicting".

I recommend you search the forums for proper shooting technique with progressive capture. Even better - don't read the video forums at all - go to the *film* forums. Cinematographers have been shooting 24p for *decades*, in fact roughly a century. No-one would say that a professionally produced motion picture film appears "stuttery". They are using the *exact* same motion qualities as your nifty little HV20... if it appears "stuttery" then I would say operator inexperience is to blame, not the means of motion capture.

Here's 6 basics to improve your HV20 experience - and with the exception of a tripod and cheap mic you can achieve all this for *free*

First, secure your camera. 24p almost always looks *terrible* when shot hand-held by amatuers. In that regard Canon almost made a mistake including 24p on the HV20. Many soccer mums probably *hate* 24p mode.
Avoid hand-held unless you are a consumate pro or you have added significant mass to the camera by pimping it with every conceivable accessory including 35mm adaptors, 15mm rods, matteboxes, LCD panels, batteries, etc... and if you have that stuff you are probably a pro anyway!
*Always* secure your camera - tripod, beanbag, steadicam, dolly, crane, whatever. Since the move to HD I have been shooting a lot more *locked* shots, usually with a wideangle adaptor on the HV20 - especially to capture city scenes and architecture on my travels. Work with the HDV compression - it likes minimal movement in the frame. I try to find an interesting angle on a building and include just a small portion of leaves or branches fluttering in the wind to indicate that it's not a still frame. Same goes for shooting landscapes and public spaces. I try to find places where people are stopping to chat to each other or peruse the city rather than busy areas with people rushing to and fro.

Second, avoid fast camera movements. Make sure any object takes at least 7 seconds to traverse the frame. The only exception is panning to follow a fast-moving subject - this is used a *lot* in modern movies - just be sure to keep the subject in the frame or you will end up with stuttery rubbish.

Third, avoid zooming during a shot. Take a close look at major motion pictures - you will *rarely* see a zoom shot - with the excpetion of cheap horror and action films and because the director can't think of a better way to draw your attention to something.

Fourth, try to keep to the long end of the zoom - you will create a narrower depth of field and your subject will be more clearly isolated. In tandem with a longer zoom, keep your apeture as wide open as possible.

Fifth, buy a cheap lapel microphone and/or shotgun. I use a $24 lapel mic from Radio Shack plugged directly into the camera's minijack for interviews. Try using one with grandma reading to the grandchildren, or on wedding guests for a "video message board" at a wedding reception. Say farewell to crappy home movies where you can't hear a single thing due to background noise, the wedding band playing in the background or babies screaming behind the camera.
Another option I use a lot is a decent base-level pro handheld dynamic (i.e. does not require phantom power) mic such as a Shure SM58 plugged directly into the HV20 via an XLR-Minijack cable (you will probably have to make it yourself) and recruit someone to be the "host" as they interview wedding guests, family members, cast members, band members or whatever it is you are filming. I find there's always a drunken uncle, cousin or friend willing to play "interviewer" and the results are often hilarious.
I wouldn't skimp out on a shotgun mic though, and if you're going to head down that path you might as well recruit a boom operator and do it properly. I shoot production shows and concerts as part of my employment and I *always* record console audio onto DAT, MiniDisc or direct to hard drive in some form or other, then mix it down later in Digital Performer and master to Dolby Digital 5.1 in Compressor. If at all possible I record a basic console downmix direct to camera as well in order to facilitate post-sync.

Finally, never underestimate the importance of lighting. I would argue that 50% of the "look" of films is in the lighting, the rest is a product of composition, lens choices, set dressing and post production. Usually lighting is the *last* consideration of the amatuer videographer.... there's always some idiot at family gatherings who objects to you setting up a light or repositioning an existing one. Doing so will turn your home movies from embarassing amatuerish rubbish into something that your descendents might someday actually want to watch. I try to use natural daylight as much as possible, even in indoor scenes. Learn to use the manual exposure with zebra on the HV20 - you will need it when shooting indoors against an overblown window - a common occurence at wedding receptions and family events. The autoexposure and backlight compensation are insufficient in most real-world situations.
At family gatherings I simply make a suggestion that we gather some people outside to enjoy the garden, or encourage the kids to play out on the lawn. They don't need to know the real reason is to get nice daylight on my shoot!

Happy shooting!

[Glyn Williams]

Originally Posted by Tim Sills

Hi All,

I have the PAL version of the HV20 so I have 25p or 50i. If I use 25p the imagery appears "stuttery" for the lack of a better word, whether viewed on a PC screen or TV. No such problem with 50i. Will pulldown remove this effect and make my 25p imagery appear smooth?
Umm, little help please guys.

Tim,
It may be that you don't like progressive footage (I love it)
But it could be your computer monitor.

If it is set to 60Hz and you are watching 25fps footage. Then you'll see something like this.
Frame 1 (will stay on screen for two refreshes)
Frame 2 (two refreshes)
Frame 3 (three refreshes)
Frame 4 (two refreshes)
etc. (22322323223232232322323)
There's no regular and even way to do this. It's quite possible that you'll notice this and spot the irregularity.
You'd be quite right to call this stuttery.

Whereas if your screen refreshes at 75hz
Frame 1 (three refreshes)
Frame 2 (three refreshes)
Frame 3 (three refreshes)
etc. (333333333333333)

Similarly 25p footage will look smooth on a PAL TV 24fps

Glyn

[Tim Sills]

Paul - sorry mate, but almost all of your suggestions seem to relate to slowing down the inter-frame movement = common-sense. Nothing new there.

The imagery I shoot in progressive looks stuttery to me because it's holiday stuff - I don't want to be restricted to very slow panning if say some sort of volcanic activity happens behind me while on a mountain trek !! You want to get it on "tape" and quickly. Also, ask yourself, can I control the lighting, etc?? Enough said.

BTW - from a physicists point of view, 25p will appear stuttery for almost all motion except that equating to very small rates of change since the human brain needs at least 50 shots per second to "perceive" fluid motion. The absolute basics of visual simulation!! All the CG type movies may be presented at 24p or whatever, but the rendering is natively at a much higher rate then reduced to fit in with the acting and corresponding film display rate.

Glyn, I have tried the progressive footage on TV, and PC screen at very different refresh rates. Still appears stuttery to me, even when this "amateur" pans the camera around fairly slowly.

The beauty of this camera is that progressive is there for those who want it, and mere "rubbish" interlaced for those who don't. It's grand to be able to choose !

Tim

[Ian G. Thompson]

Originally Posted by Tim Sills

Paul - sorry mate, but almost all of your suggestions seem to relate to slowing down the inter-frame movement = common-sense. Nothing new there.

The imagery I shoot in progressive looks stuttery to me because it's holiday stuff - I don't want to be restricted to very slow panning if say some sort of volcanic activity happens behind me while on a mountain trek !! You want to get it on "tape" and quickly. Also, ask yourself, can I control the lighting, etc?? Enough said.

BTW - from a physicists point of view, 25p will appear stuttery for almost all motion except that equating to very small rates of change since the human brain needs at least 50 shots per second to "perceive" fluid motion. The absolute basics of visual simulation!! All the CG type movies may be presented at 24p or whatever, but the rendering is natively at a much higher rate then reduced to fit in with the acting and corresponding film display rate.

Glyn, I have tried the progressive footage on TV, and PC screen at very different refresh rates. Still appears stuttery to me, even when this "amateur" pans the camera around fairly slowly.

The beauty of this camera is that progressive is there for those who want it, and mere "rubbish" interlaced for those who don't. It's grand to be able to choose !

Tim

That's just it Tim...it's holiday stuff. 24/25P is not good for that kind of stuff (subjective I know). Those frame rates are to mimick the cadence of film (I know you said this is common sense but in all actuality...Hollywood films are "stuttery" also...so that's why 24/25P is more suited for narrative work...with the slow pans and all). Watch and take note in some of your Hollywood DVDs and look at some of the panning and camera movements...not very fast at all...and even if they are the cam is always focused on a moving object. There are rules of thumb to follow in 24/25P. Because 50i/60i is more fluent in its cadence it is used more in documentaries, wildllife videos, sports, birthday parties etc. So...if your just more of a point shooter then stick to 50/60i cause when you go into the other mode there are different rules to follow when filming.

Edit: Here's a form of checks and balances...take a look at some of the HV20 videos you see at this site. Most are in 24P. Check and see if they are more smooth than what you are seeing with your video. If so, then it might be in how you are filming (just a thought).

[Joseph H. Moore]

The beauty of this camera is that progressive is there for those who want it, and mere "rubbish" interlaced for those who don't.

Just for the record, the motion isn't smoother because it's interlaced, it's smoother because you're recording an image (even if it is half of an image) 60 times a second instead of 24 times a second. Nobody looks at 60p and thinks its not as smooth or smoother than 60i.

But yes, it is wonderful to have a choice!

[Ian G. Thompson]

Also Tim 50/60i gives you that "reality" look...as you suggested in how much frames our brain needs to see per second to get that look. That's why movies don't have that "reality' look to them...if they did then it would give us that daytime soap opera look. Once again...I know this is common sense but i just think you chose the wrong mode to film your stuff in.

[Tim Sills]

Ian - all of this 25p stuff I talk about is with respect to testing - the holidays I use to plan it with are some 6 weeks away yet. Just so I know what I can and can not do with the HV20. Better safe than sorry I guess hence critical testing using progressive versus interlaced.

Yes, movies are shot the way they are with combination of focal length and aperture to provide desire depth-of-field and what not. Yes, can be very different to reality. Speaking of, the HV20 FOV is a bit to narrow for my liking. At 41 or 43mm it's a bit close to the human eye, quoted by Canon as 50mm I think. Looking at the WD-H43 shots though, the extra FOV comes at the expense of horrible barrel distortion...

Joseph - I never said motion is smoother because it's interlaced. I said it's smoother because there are more samples, shots if you will, per unit time. If there was a 25i mode it too would look "stuttery" (at least to my eyes). Stick the camera in Tv mode with a 1/25th shutter speed and watch The fact that the interlaced shots are at half the resolution is of little concern. It's amazing what the brain fills in for you.

I don't think we can simply say that ALL Hollywood movies are progressive and not stuttery so there's some perceptual issue here. Watch something computer generated like Shrek and alot of the image is very smooth - the DOF is very much exaggerated but admittedly it's all synthetic. I have watched a good number of movies in my DVD collection of late and deliberately looked outside the focal point (whether it's a vehicle, object or otherwise), and only some have that stutter, albeit to a lesser extent. The effect I speak of doesn't seem to be there or not - it's not all or nothing.

Again, choice is wonderful. I does seem however that we approaching the point where we can agree that progressive has it's merits (and times where it is preferred), and the same for interlaced.

[Glyn Williams]

Tim,
The thing is, the change in technology means we are losing interlaced displays.

Computer CRTs are progressive. Computer LCDs are progressive, and in turn so are Plasma screens and LCD TVs. You are going to struggle to buy an interlaced device.

With these displays, the interlacing is lost (ie you never see both fields at the same moment).
Instead each field is interpolated to a full progressive frame. Or in some cases averaged with the previous field. What you are actually getting is 50fps progressive with halved vertical resolution.