Potential/rumored Chromakey issues with HDV!

[Thomas Smet]

This isn't about if it can be done or not but that it may not turn out as good as it might from another camera. I have dealt with a lot of footage like this for a long time as well which is why I know that it can be an issue. While it can be dealt with in my experience it is best to avoid it if you can. Not everybody here uses Cineform so that isn't an option for everybody.

There may be a lot of people who will look for a camera to use for keying and I just want them to know what they may be facing if they decide to go with the SONY V1. This isn't about subjective quality or not but the fact that the chroma is either as good or not as good as that from another camera. How is that subjective? I think people should know about this issue up front instead of getting the camera and then spending months on here trying to figure out how to deal with this type of chroma because they are not used to all the methods of dealing with subpar chroma. When I say subpar I do not mean from just this camera but any sub 4:2:2 camera which means every DV and HDV camera.

I have done some amazing stuff with DV and 4:1:1 that people said could not be done but I did it anyway. It looks good but it could have looked better if I had 4:2:2 or even progressive 4:2:0. If you give me interlaced 4:2:0 I can make it look very good but with progressive 4:2:0 I could make it look even better.

DSE I would really like to see a few raw samples of your green screen footage from the V1.

Originally Posted by Don Donatello

you have similar interlace artifacts when keying FILM transferred to tape .
the pull down always gets in the way when keying and you have to work harder getting a good key .. remove the pull down and the interlace artifacts go away ... convert the m2t file using a intermediate ( cineform) then use combustion/AE to remove pull down and key it ...

The issue is only the same if you are talking about film transferred to a 4:2:0 tape such as PAL DV or HDV. If the film was transferred to a 4:2:2 tape then no this isn't the same issue. If it was transferred to PAL then there wouldn't be any pulldown issues so what kind of tape are you talking about here? This is strictly a 4:2:0 issue and the only US based tape format that would use pulldown with 4:2:0 that I know of would be HDV tape and I do not know a whole lot of films that are transferred to HDV and then edited.

[Don Donatello]

if i remember correctly back in late 90's to early 2000's many were complaining about DV's 4:1:1 color space. at that time persons were saying PAL's 4:2:0 color space was slightly better and one could key it better ??

IMO the main problem with green screening 4:1:1 are the hand size camera's ( 1995- 2003 models) switch to a good 2/3" chip camera and your 4:1:1 & 4:2:0 just got alot better ... over the past 2 years keying software ( made specifically for keying) is much better and interview type shots can be keyed very good on 4:1:1/4:2:0 hand size camera's including HDV ...

bottom line for good keys - use the right tools for keying .. know the limits of your camera & keying software for keying ...

4:4:4 is always better keying then 4:2:2 .. and 4:2:2 is always better keying then 4:1:1 /4:2:0 .. where 3:1:1 fits in ? you got me but i know many that use HDcam material for keying ...

[Thomas Smet]

Originally Posted by Don Donatello

bottom line for good keys - use the right tools for keying .. know the limits of your camera & keying software for keying ...

4:4:4 is always better keying then 4:2:2 .. and 4:2:2 is always better keying then 4:1:1 /4:2:0 .. where 3:1:1 fits in ? you got me but i know many that use HDcam material for keying ...

And thats exactly what I am doing is pointing out the limits of this camera. Think of this as more of a heads up. I'm not trying to get people to not buy the camera. I'm just trying to make them aware of what they will see with the chroma so they are not shocked when they notice it. Of course most people think that is just the way 4:2:0 looks because DVD's, PAL, and most forms of HDV have this same issue. I'm just pointing out that if your main aim is compositing then there may be other choices out there that may give you better results.

[Heath McKnight]

I'll say this, when my friends chromakey in DV, they make it 4:2:2 and they've told me keying HDV, 4:2:0, is nice, but they make it 4:2:2, as well. I'm not an F/X genius, sorry.

heath

[Steve Mullen]

Originally Posted by Thomas Smet

And thats exactly what I am doing is pointing out the limits of this camera. Think of this as more of a heads up.

I've got a V1. Can you explain exactly what you HOW you want the V1 tested and I'll try to run the test. Right now, I just don't see what you are concerned about. My calculations do not indicate reverse pulldown should be a problem.

[Douglas Spotted Eagle]

Originally Posted by Thomas Smet

And thats exactly what I am doing is pointing out the limits of this camera. Think of this as more of a heads up. I'm .

Sorry, Thomas; I think it's important to draw a distinction that you're saying this about the format, and not the camera. You don't *know* squat about this camera, as you don't have it in your hands, and won't have one in your hands for a while yet. You may or may not be right, but at the moment, it's rumor, not fact. I realize you won't accept that for now, but the fact is, you don't have one, you don't have footage, and it's all speculation at this point.

Originally Posted by Steve Mullen

I've got a V1. Can you explain exactly what you HOW you want the V1 tested and I'll try to run the test. Right now, I just don't see what you are concerned about. My calculations do not indicate reverse pulldown should be a problem.

Steve,
if you've got the V1 I think you have, be sure to clear the camera profile, or load a profile from the memory card. If it's the one I had, I left a couple pic profiles and cam profiles, a couple of which are a little unique (read "strange").

[Thomas Smet]

Originally Posted by Douglas Spotted Eagle

Sorry, Thomas; I think it's important to draw a distinction that you're saying this about the format, and not the camera. You don't *know* squat about this camera, as you don't have it in your hands, and won't have one in your hands for a while yet. You may or may not be right, but at the moment, it's rumor, not fact. I realize you won't accept that for now, but the fact is, you don't have one, you don't have footage, and it's all speculation at this point.

I did say this in my very first post. I mentioned that this has nothing to do with the camera itself but the way mpeg2 works. It just so happens the V1 uses that form of mpeg2. I have tried pointing out many times (more so than a lot of other people do) that I am not attacking the camera at all. This is not meant to be a negative post at all but more of a informative post on what people can expect from this type of chroma. It has been everybody else that assumes it is negative and that starts to make it seem like a negative post. I do not need to know anything about the camera because the camera isn't in question here but the form of mpeg2 it records. I do not care what is in the camera in terms of chips, size, bla bla bla. I only care about the image and what I know of mpeg2 says that putting a progressive video in an interlaced mpeg2 video uses the not so good form of mpeg2. I am not the only person that knows this. Adam Wilt has articles on the subject. I tried posting links to them at one point in another thread but they got removed. Graeme Nattress has even talked about how bad interlaced mpeg2 is compared to progressive mpeg2.

Could the chroma on the V1 be better by using true progressive mpeg2 encoding? yes. But at the same time I did defend the decision by SONY because of the older HDV gear. This really is the only way it could have been done so the tapes could playback in the current HDV decks.

If you want to consider this a rumor thats fine. I am not trying to spread rumors here but bring up a well known issue of what happens with interlaced mpeg2.

Originally Posted by Steve Mullen

I've got a V1. Can you explain exactly what you HOW you want the V1 tested and I'll try to run the test. Right now, I just don't see what you are concerned about. My calculations do not indicate reverse pulldown should be a problem.

This has nothing to do with pulldown at all. It is even an issue with 25p and 30p like I have mentioned many times already. mpeg2 uses two different patterns of chroma sampling for interlaced and progressive video. HDV1 always uses progressive. HDV2 is interlaced by nature so it always uses the interlaced form of sampling. Canon tricked the format so their F modes would use the progressive form of chroma sampling but that is why the tapes will not play in any other camera or deck.

Shoot any scenes with deep colors that contrast against each other. For example a red ball on a blue carpet. Pretty much anything with a lot of color will show this. Try it on interlaced and progressive video and you will notice the same chroma banding as in my example image.

There were two videos posted on the DVXuser forum from IBC that were shot with the V1E. One was 50i and the other was 25p. Both videos including the 25p showed the same type of chroma. I had hoped the 25p would show the better progressive form of chroma but after reading that the SONY puts the progressive video into an interlaced mpeg2 stream for better compatability of current HDV equipment it all made sense to me.

I do not want to post any links because I do not want to violate anything but do a search for "chroma upsampling error" or try to find some of the articles from Adam Wilt or Graeme Nattress.

Again if anybody here has any raw images that can show me that the V1 does in fact use the progressive form of mpeg2 encoding I would be very gratefull. I would love more than anything to be wrong.

[Steve Mullen]

Originally Posted by Douglas Spotted Eagle

Steve,
if you've got the V1 I think you have, be sure to clear the camera profile, or load a profile from the memory card. If it's the one I had, I left a couple pic profiles and cam profiles, a couple of which are a little unique (read "strange").

Thank you. What a great camcorder!!!!

Do you understand what Thomas is concerned about?

I understand that each field in encoded individually, and one carries Y & CB and other Y & Cr. Is it the concern that since each is encoded seperately the encoding is bound to be "different" so when the fields are decoded and placed back into a frame -- Cb and Cr information won't exactly line up perfectly with the Ys?

Wouldn't it happen with all interlace MPEG-2? And, if so -- how come no one seems to have worried about it?

Or, is he simply saying that progressive MPEG-2 encoding is inherently better than interlace MPEG-2 encoding? I'll buy that because progresive has lots of advantages -- but clearly with over 90,000 1080i HDV "pro" units in the field -- how bad couldthis issue be?

I do know that Apple's AIC is supposed to be bad on interlace but fine on progressive -- so this is not the first time I've heard it. But, I though that was a codec issue.

Best Regards,
Steve

[Douglas Spotted Eagle]

I do understand what Thomas is talking about, and bothered that he assigns it to this camera when it's an issue for all HDV overall. And it's a minimal "issue" if that word is to be used at all. Sort of like having unmatched tires on the front/back of your car is an "issue" but the truth is, millions of people drive every day with unmatched tires. Which in my mind, makes it a non-issue.

There is the argument that the two fields might not line up on decode, but given the way the encode works, I don't accept that argument. You'll do your own tests of course, but I'm not seeing issue with anything I've shot, and I've already sent both greenscreened work and handheld/tripod-shot work off to be broadcast from the very camcorder you have in your hands. CNN, ESPN, ESPN2, Fox Sports, MSNBC, and ABC Good Morning America have all broadcast that footage with no comment from any one other than the engineer from ESPN2 saying "What did you shoot this on, it looks incredible." Aside from the V1, this is a common reaction to great skydiving footage anyway.

The argument being used is true for all interlaced mpeg, and therefore it's irresponsible to assign the issue to this specific camcorder, IMO, which is why this thread really belongs in Area 51 instead of here. No one seems to have worried about it, because it's not anywhere near the issue that Thomas and this thread make it out to be. It's more measurebating and slide rules vs reality, and it makes me wonder (once again) how many folks on these boards are actually shooting video vs screwing around with calculators and generated media such as Thomas shows earlier in this thread. If we go by math alone, then airplanes shouldn't fly either. That doesn't mean I'm opposed to understanding the guts and fringes of the technology; I think I've amply demonstrated I'm into that, too. But as you can see by what you're holding in your hands, all the technical arguments fly out the window based on what your eyes actually see. Isn't that what it's truly all about? Perception of image vs mathematical models of pixels combined to generate a visual instigator?
Have fun with the V1. I surely did.

[Steve Mullen]

Originally Posted by Douglas Spotted Eagle

There is the argument that the two fields might not line up on decode, but given the way the encode works, I don't accept that argument.

I'm not sure I do either. Or, rather when I understand it -- which I don't yet -- I suspect that given the installed base of 1080i it simply can't be that big a deal.

What I think Tom is saying -- which is why it IS relevant to the V1 is: If you are buying a V1 to shoot 24p you would do better chosing a Canon or JVC -- all else being equal. But, all else isn't equal so the argument isn't very powerful.

I'm all for technical discussions, but part of that has to be how visible is an artifact. One can be 100% technically correct about something that is insignificant.

And, math shows why airplanes fly. It's bumblebees.

Best Regards,
Steve

[Greg Boston]

Originally Posted by Steve Mullen

And, math shows why airplanes fly. It's bumblebees.

Don't forget helicopters, the math shows they shouldn't fly either. That's what gave rise to the urban myth that helicopters only fly because they're so ugly that the earth repels them.

-gb-

[Marcus Marchesseault]

I can't help it:

There is plenty of math involved in designing airplanes and helicopters. Math is what makes the behavior of the final version fairly predictable when it first takes flight. Heck, there is so much math that the actual motion of air molecules is plotted and simulated as a mathematical-imaginary wing passes through the mathematically-generated environment.

Bumblebees achieve sufficient lift by utilizing vortex flow. The vortex created has more lift than could be accounted for from the lift system of an airplane wing or helicopter blade. Perhaps we will one day have aircraft that generate lift from vortex flow...

It may not be a problem to have different tires on your front and rear axle, but NEVER PUT DIFFERENT TIRES ON THE SAME AXLE. I bought a used truck with this condition and it had horrible road behavior. One of the front wheels had a strong tendency to lock up while braking. I changed the whole set the next day.

********

I think the most important points brought up in all this are twofold:

1. Current software has been developed to do decent keys with SD DV footage and HD footage, even interlaced, will look even better. The software has been designed to compensate for interlacing.

2. Whether it is due to a mathematically quantifiable phenomena or simply an optical illusion, it is the final perception that matters.

I have seen decent chromakey done on interlaced FX1 footage from the stock Vegas software by a user that had never done chromakey before in front of a greenscreen leaning up against a garage door. I'm sure a high-end plugin and a properly-lit screen will give the Average Joe amazing capabilities.

[Heath McKnight]

I am not the best with math, but I trust my eyes, and that's how I'll be judging the V1, along with comfort, design, etc.

heath

[Steve Mullen]

Reading up on CUE and ICP it seems that both come from poor design of encoding and decoding operations, respectively.

Since there is no way to know what the software will do on decoding, there is no way to predict that you are going to have CUE or not. I know the AIC has the problem. But, CineForm may not. And, it's not clear what the various HDV decoders that are used in Native NLE do. Since this a function of what NLE you choose -- it hardly seems reasonable to bring this up under a V1 thread.

ICP is a function of poor setting of encode flags. This a problem with movies made into movies. There's no evidence that the V1 sets the flags incorrectly. In fact, given a hardware encoder is used -- it's very unlikely. So why is this in the V1 thread?

Now it's possible your NLE may screw-up flags. But, that's why you need to buy your NLE carefully. Like, do not use AIC with FCP if you have interlaced video. This is an NLE issue.

On the other hand -- CUE and ICP are just a few of the many artifacts that come with interlace video. It's why I prefer progressive. It's why the world will eventually switch to progressive. So if you want pristine video, only work use progressive. But, obviously of the 25 HD channels on DISH, only 3 are progressive -- so the desire for pristine video is clearly lower than the desire for greater resolution, or the ability to claim greater resolution.

But you raise the issue in the context of 24p within 60i. First, since it's an NLE implementation issue it's not a given. A worry yes. But, not a certainty.

I think folks need to really learn about how their NLE does decoding, scaling, and aspect-ration conversion. Simply buying FCP cause everyone else does may be a very poor idea. You may want to consider an NLE designed for professionals by engineers who really understand MPEG-2. And, given high-definition DVD are coming fast, you might want to be sure it creates AC-3 soundtracks within the application. And, HD DVD templates and buttons.

[Thomas Smet]

This is true that it comes down to the decoder. The only reason I brought it up is that this is the only HDV camera where the issue may come up if the mpeg-2 decoder in the system doesn't do it right.

If the decoder does work right then progressive video from the V1 should work great.

I did not mean in any way to attack the camera because I really do think this is going to be a great camera. But I think this is the only HDV camera this can happen with and I hope to inform people on how to take the steaps to deal with it. Perhaps Vegas decodes the video properly and it all works great.

I can say from new tests that if you have a decoder doing it the right way then the chroma will be fine and should work great for keying. Well as great as HDV can be anyways. If you do not have a good decoder then this issue may come up in some 3rd party applications. The only reason why I sadly put this on the V1 is because sadly the V1 is the only camera that puts a 24p/25p/30p video inside of an interlaced stream. It really is the only HDV camera where this could show up if you do not have a decent decoder.

The thread could be put somewhere else but this issue may only ever come up for V1 users and I want to make sure they can take the steps to make sure they do not have any problems they may face.