30P - the Forgotten Mode

[Stephen van Vuuren]

Probably due to marketing and the sexiness of 24p, it seems like the 30p mode on the DVX100 is rarely talked about or used (I've yet to see many grabs clips shot in 30p).

Especially in the "I don't need 24P" discussions, 30P is often just lumped as as like 24p but to my mind it's not at all.

(1) 30P has 20% greater temporal resolution, so less subject to panning, strobing than 24p
(2) 30P can be edited on any system
(3) Progressive scan produces a sharper image than interlaced and gives a different feel to 60i footage without the dramatic change to 24p and editing issues.
(4) 30P and 60i footage will mix together easily and seamlessly in the same timeline of any NLE - so you can shoot 60i when you need it and then go back to 60i

It seems like corporate and event shooters would love 30p. It also seems like a very worthwhile upgrade from the DVC80 which still looks to me like a news/journalism cam.

Comments? Who's shooting 30P?

[Stephen van Vuuren]

Forgot one point:

(5) 30P offers exactly that same look of "Frame Mode" on the Canon etc. cams with 33% more resolution and better low-light response.

[Barry Green]

There used to be some discussion over on dv.com, where people would say "24P is stupid, 24P is overhyped, but 30P, now there's a good idea..."

30P is good for the reasons you mentioned, especially in that you don't need to use a special editing program or worry about pulldown or split frames, etc.

It also has some drawbacks:

1) cannot be converted to PAL
2) cannot be transferred to film
3) No option of shooting at a higher frame rate for the slow-mo effect (i.e., shooting 24P, you can switch to 30P for a slight slow-mo effect)
4) No space savings possible on DVD's (i.e., 24P DVD's let you fit 20% more on the disc, 30P would offer no such advantage).
5) 24P gives you the option of a little more low-light sensitivity (slower shutter speeds than 1/30th).

So 30P definitely has some advantages, but for the reasons listed above I usually don't shoot it. It would be interesting to hear what criteria others use to decide between 30 and 24...

[John Britt]

When comparing the DVC80 and DVX100, it was actually the 30P mode that really interested me most about the 100.

Since my work is straight-to-TV, it seemed like a great way to get a "film-like" look w/out fussing w/ 24P (which looked like a great idea for indie filmmakers, but not for me). Plus, as you said, it would be easier to cut w/ 60i footage. Reviews and user-opinions, though, didn't talk much about it...

Ultimately, the near-$1000 difference in price made the decision for me.

Still, I'd like to hear how people are using 30P (if at all) especially for use on television.

[Alex Dunn]

Call me crazy, but I was under the impression that in order to render a DVD compatible file, it has to be in NTSC which is 29.97fps or 30p. So what's with this 20%more claim? Once it's converted, I think you lose your 20%.

[Dany Nativel]

No you don't have to make it 29.97fps. That's the beauty of the 24p mode and pulldown flag used on DVDs.
- PAL DVD can only be 25fps (50i).
- NTSC DVDs can be 29.97fps (60i) or 24fps (23.93p)

You do everything in 24p and burn the DVD with the 24p footage but with a special flag that will tell the DVD player to consider this :
- as a 24p footage if you have a progressive scan DVD and TV (lucky you're).
- as a 29.97fps stream (you need that frame rate in order to watch it on your "old" tv". So the DVD player will do the pulldown for you in order to restore a 29.97fps framerate.

I did that on a DVD using a XM2 (PAL version of the GL2). Shot in frame mode (50i that gives a fake 25p).
I worked on the editing using PAL DV 50i but remembered it's already de-interlaced due to the frame mode. Created a new "NTSC 24p" project , imported the 50i (aka frame mode 25p) then slowed down the all thing by about 4% to get the 24p. Finally made a 24p DVD with the resulting MPEG file that contained the necessary pulldown flag.

This process gives me the option to have both NTSC and PAL DVD without any fancy motion artifacts due to resampling. I can also save space on NTSC DVD.
So can the 30p give me the same flexibility ?

PS: I don't why I'm asking the question as I'm not planning to switch to the DVX but who knows?

[Peter J Alessandria]

I love 30p. I've used it for some music videos. The big advantage for me is that it slows down nicer than 24p but still has that filmic look. That being said, I just started shooting a short comedy but decided to go with 24pN. I don't plan on using any slow motion effects in the project. Plus I sold my cast on shooting "24p" :-)

[Dale Anthony Smith]

I'm working on a direct to DVD project and shooting in 30P. The beauty part is that it will be shown in a progressive environment...(DVD interactive) and the "alternate field" thing. My recent Hi Def show was in a film festival a few weeks ago and they were unable to set up for HD projection. They wound up making a DVD out of it and showing it NTSC letterbox. At the end the title crawl was "jumping" and someone in the audience asked about it. After the show a techie came up to me and offered the explanation that the DVD assigns "even" or "odd" field to start... it was showing the title crawl (and the rest of the show) literally in reverse order with regard to fields. WITH 30P BOTH FIELDS ARE THE SAME!!. So it makes sense for the DVD stuff to be progressive. I also shot exteriors last weekend in both 60i and 30P and the 30P stuff looks far better with regard to contrast and detail. It Looks more like film. 30P is my favorite mode for the DX so far.

[Barry Green]

In 30P, both fields are not the same. They're captured at the same moment in time, but they have different information in them. Half the picture is stored in each field. If they were the same, your picture would be only half the potential resolution, and that's not the case.

The fields are definitely very different info. They're just captured at the same instant in time, so there's no motion offset, but there's definitely different information in them.

[Frank Granovski]

Shooting regular interlaced means shooting fields, not frames: odd, even; odd, even; etc. There is also a time lag between each field. 30 progressive, on the other hand, captures 1 frame per sweep so there is no lag within a frame. However, 30P skips every 2nd sweep.

Yes, I shoot 30P (29.97P) sometimes and I do notice sharper resolution when I play back interlaced on my TV. I guess it's because it captures at a higher resolution, both with vertical and horizontal. My pro-scan 1 chip plays back about 440 horizontal lines but in pro-scan it's 500 lines.

The closest thing I have to 24P is using frame mode on my PAL cam. :)

[Andre De Clercq]

I suppose many people look at their 30P footage on a TV screen. In that case I wonder why those people find 30p better ("sharper") than 60i. We have to considder two different situations: still pictures and moving images. Still pictures are exactly the same if shot at 60i or 30p when displayed on an interlaced CRT mode. Both show the same resolution and both show interline flicker. If there is motion in the picture, resolution is not an issue mainly because of two elements: moving object show motion blurr which destructs resolution, unless they are taken at high shutter speeds which is generally not advisable, specifically for 30p because of higher stutter visibility with high speed shutter settings. The only difference is a different kind of motion blurr which is maybe somewhat cleaner at 30p

[Stephen van Vuuren]

Good discussion all - since I've don't shoot 30p I've been interested in those who have.

Andre:

30p and 60i in stills are in fact not identical - most CCD's apply filtering to reduced interline twitter causing a loss in resolution (see current Adam Wilt column in DV mag for more details.)

The difference will vary depending on CCD and may not be noticably in some viewing envirorments, but progressive scan does increase resolution vs. interlaced in all scenarios.

[Andre De Clercq]

Stephen, I suppose we are talking about vertical resolution only. I know the vertical filtering techniques very well, but all cams apply some vertical convolution filtering. The pro ones apply optical prefiltering. Line twitter(interlace flicker) and crawl effects would be awfull if a progressive (or an interlaced) footage would be played back in an interlace mode and this filtering would not be applied (re some electronic testpatterns) That's why in the DVX100 manual (pg38) the "thin" mode is advised to be set off. LCD, DLP... is another story but I specifically mentioned interlaced CRT viewing of prog footage.

[Laurence Kingston]

Does anyone know how upconverting DVD players or the uprezzing routines in HDTVs handle 30p? Do they even know it's not 60i? Do they try to deinterlace the already progressive image? Do they uprez with the same quality as they do with 24p?

[Mark Donnell]

I use 30p on the DVX-100A almost exclusively, partially because most of what I shoot is sports. I like a sharp frame advance for replay. Andre - your comments about watching 30p on a television are generally correct, but I have a high-end Sony 32" CRT TV and it has the option of viewing still images as either field or frame (probably by digitally storing two fields when in the frame mode). The difference between 60i and 30p on this TV are significant.