24p Pulldown Problem or Tempest in a Teacup?

[Erik Bien]

I ran across this discussion (http://www.dvxuser.com/V6/showthread.php?t=103092) on another site and thought it might be of interest here too ...

[Ian-T]

Erik....thanks for bringing this thread to our attention. Honestly...it is a non-issue. I must have shot a tom of HV20 footage over the last few months....and I have never seen this problem. A theory is one thing....but evidence is another. I don't doubt Mr. Newman is knowledgeable(sp) in what he does butl like I said...evidence is key.

To me it can turn into what i consider a "wobble theory"...that is....the wobble caused by rolling shutter....I doubt that.. The wobble is caused by faulty OIS in my opinion....and the Canon brand of cams (from what I understand) always had a problem with the OIS not really fully turned off (even when you turn it off). I read somewhere earlier where a user stated that he always had Canons and his Canon Optura displayed this same sort of wobble (probably not to this extent...I don't know)....but...I mention this because that particular machine is a CCD camcorder. Rolling Shuttter has its own freakiness..(that crazy slanting of the video we see when panning too fast) but the wobble that we all have seen i other peoples videos is something else. Think about it...why are some of us getting it and some of us (like myself) not??? I've seen tiny wobbles in my cam at very low frequencies (zoomed out while sitting my cam on my caar door when running....very tiny shakes)....but not to the extent of what I've sen in some of those notorious videos.

[mik]

there's only one case we can't test for (just canon could). if the ois is very fast it could move during cmos' save. the ois should be locked during the save time of the cmos. otherwise if it moves during the save, different parts of the sensor receive different optical images.

i say it probably is a 70-30 situation. the rolling shutter with a non locked ois = wobble (to be technically true you get a worse wobble with the ois than without).

[Erik Bien]

Well, the "chroma bleed theory" (as I too am comfortable calling it until someone can show me footage, not just frame-grabs that exhibit a visible effect) shouldn't pose a problem except possibly for chroma-key or other effects work, or so the egg-head who first noted the possibility claimed.

But I should point out that this is a DIFFERENT issue ENTIRELY than the "rolling shutter artifacts" which do indeed create bizarre footage under certain circumstances. (I don't have the link handy, but if you've ever seen the "Jell-O Cam" footage that resulted when one HV20 owner shot aerials from a helicopter you know just how awful the worst-case scenario can be).

At this point I'd categorize the rolling shutter as a "known issue," at least when the camera is subjected to high-frequency vibration, but I've yet to see properly reverse-TK'd 24p footage from the HV20 that shows any visible artifacts of this "chroma bleed" that I can detect (standard disclaimer, I don't do post if I can avoid it, and my computer monitor sucks).

[sean90291]

Well, the "chroma bleed theory" (as I too am comfortable calling it until someone can show me footage, not just frame-grabs that exhibit a visible effect) shouldn't pose a problem except possibly for chroma-key or other effects work, or so the egg-head who first noted the possibility claimed.

But I should point out that this is a DIFFERENT issue ENTIRELY than the "rolling shutter artifacts" which do indeed create bizarre footage under certain circumstances. (I don't have the link handy, but if you've ever seen the "Jell-O Cam" footage that resulted when one HV20 owner shot aerials from a helicopter you know just how awful the worst-case scenario can be).

At this point I'd categorize the rolling shutter as a "known issue," at least when the camera is subjected to high-frequency vibration, but I've yet to see properly reverse-TK'd 24p footage from the HV20 that shows any visible artifacts of this "chroma bleed" that I can detect (standard disclaimer, I don't do post if I can avoid it, and my computer monitor sucks).

Not sure who the egg-head is you refer to, David Newman of CineForm or me, the guy who opened up discussion on DVXuser about the question. You seem to be taking it personally or something. The HV20 is a great little camera. HDV has some technical shortcomings (most codecs do) which professional egg-heads and professional artists will need to take into account. The HV20 is not designed or marketed as a "pro" camera, so not surprisingly many people who use it will never notice the chroma-bleed issue after pulldown. Heck most people with the HV20 will NEVER extract 24p from their 60i footage. The benefits at a consumer level are almost NIL.

But it makes me wonder what brand and resolution of monitor are you using? What is your delivery format? Oh, your laptop computer LCD is your monitor and you're delivering to YouTube, you say? Well then, chroma bleeding doesn't exist. But if you're shooting a green screen shot and you wanna try this cool little HV20 camera with an amazing sensor for a feature to be blown up and shown at Sundance...well then maybe you wanna defer to the egg-heads who will ensure you get the best result for your one shot at making a sale to distributors. The reason I care about chroma bleed is I sell the stuff I shoot and produce for broadcasters, and while I like to use alternatives to expensive cameras (the HV20 is a stop-gap diversion for a number of people until Red arrives on the scene) I need to know as much about them as I can.

Oh, and let's not forget the cool potential to reduce or eliminate such HDV "artifacting" (in this case "chroma bleed") by recording footage from your HV20 directly out an HDMI port to a disk. Again, not an ordinary feat for regular consumers. Only egg-heads need apply. I think you said it all in your words above: you don't do post and your monitor sucks. And clearly you have no idea just how exacting and demanding professional level cinematographers are about the quality of their footage. They will pick apart artifacts and color sampling that ordinary humans will never notice...not on a conscious level at least.

[Erik Bien]

LOL,

I intended "egg-head" as a more-reverential replacement for "some guy," since I couldn't remember with all of the cross-referencing and back-tracking to various forums who deserved the credit for discovering it! I suppose I should go back and edit "egg-head" to read "David Newman, CTO of CineForm and all-around video-capture guru" since that's closer to the spirit of what I intended ...

I freely admit I'm only dimly aware of the debate raging about whether CMOS cameras will be suitable for effects shooting: I'm not an "expert" in much of anything, but when I'm a cog in a larger production machine I'm normally confined to the art department designing, building and painting stuff. I'll probably do some 2nd unit shooting with an HV20/Brevis25/Nikon setup on a documentary next month, but when those same producers take delivery of their RED one and start production on their feature, the title I'm angling for is Production Designer, not Director of Photography!

I meant to hold the door open for someone with more experience and better equipment to say "No, it's a real problem viewed on my calibrated studio monitor, much worse than HDV camera X," not to declare that if I can't see it on web-posted clips that it must not exist!

Quite the contrary, I read these forums obsessively hoping to find the known limits of the camera so I don't ask it to do something it isn't good at (like aerials from a helicopter). It sounds as if chroma-keying from tape with the HV20 is going to be one of those things. If this issue (by the way, since explained more clearly by the aforementioned genius/egg-head/guru/CTO David Newman on the other board) creates problems under other circumstances, I'd like to know that, too. :hv20-smilie24:

[sean90291]

Ah, thanks for clarifying. And without a hint of sarcasm, either. Cool. I certainly didn't wanna get in some flame-type exchange with a fellow HV20 lover. ;-)

In the end, I don't think David Newman of CineForm meant to suggest that it's the HV20 that results in any "mysterious chroma bleed." It's simply the nature of interlaced HDV from ANY camera when it's deinterlaced. Healthy skepticism is a hallmark of a healthy society! So I appreciate your demands for PROOF. I guess I just will defer to guys with eggier heads than me, because I don't have a green screen shoot planned to test the theory. If I use the HV20 for a green screen shot for anything important, I'll probably record via HDMI. In the meantime, my deinterlaced HV20 footage is indistinguishable from the original HV20 footage, and I've experimented with CineForm Neo HDV, Avid's fluidfilm deinterlacing effect, and 3Prong's deinterlacing plugin. I'm leaning toward CineForm Neo HDV for the really nice result and the options and ease of use. $249 doesn't seem so bad compared to the very complex steps required to use the free programs out there.

[Erik Bien]

Sean,

No harm, no foul: in fact, I am practically jumping for joy that someone of your experience has already tried multiple reverse-TK workflows, examined the results with pro equipment and even more, a pro eye and found no visible problems (beyond those of other HDV format cameras). GREAT NEWS! :hv20-smilie84:

[Erik Bien]

At the risk of resurrecting an old dead horse ... :hv20-smilie84:

Barry Green and David Newman have addressed this issue again at one of the other HV20 forums (http://www.dvxuser.com/V6/showthread.php?t=104714).

[tiloprobst]

This guy is flooding webpages with his absolutely pointless "discoveries". That guy is really interesting, he claims to be the only one on this planet to know that the HV20 sticks pseudo-progressive footage in a 60i or 50i container. While this is not too bad in 25 FPS countries, it will require a pulldown in 24 FPS ones.

Halleluja, gratulations, this really changed my view on life. Maybe some average camcorder purchaser did not know that. And yes, you will have quality loss because of the pulldown, but not in PAL world, thank you.

What really pisses me off is not that he claims Canon is doing false marketing. One, other manufacturers do that too. Two, he is only right for pull-down countries. Three, the 25P/50i footage I've shot is beautiful and I've no reason to complain about a 950 Euros handycam. Four, he says that the HV20 does not record progressive footage. True, it sticks it into a container. But you can *produce* progressive footage from that, and at least in non pulldown PAL countries the result is perfectly progressive.