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Some more ex3 chroma key questions.

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Michael Pruitt-Bruun
Some more ex3 chroma key questions.
on May 1, 2011 at 3:29:35 pm

Hey,

i posted last week regarding using the ex vs an hpx500 for a green screen shoot, and advised my client to go with the '500 even though that cuts me out of the rental. however it looks like they may want to use my ex anyway.

given that the ex won't provide the improved color space of the '500, are there detail settings i can apply that may still aid in the compositing process? i'm assuming that reducing detail in certain ways could help smooth out the key a bit and perhaps mitigate some compression artifacts. however i can't say i really understand the interaction between the various detail controls.

also, 1080p? the project is destined for a WNET educational website, wherein our talent will present certain interactive elements. i'm not after progressive for the sense of motion, i'd rather it be smoother actually. but i have read that down-rezzing interlaced can sometimes produce further artifacts and twitter.

thanks in advance.

Michael


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Craig Seeman
Re: Some more ex3 chroma key questions.
on May 1, 2011 at 3:54:36 pm

Please read this from Juan Martinez, Senior Manager Technology, Sony.
http://forums.creativecow.net/readpost/142/856535

Basically since the samples are very close together in the EX1 MEPG2 Long GOP 4:2:0 due to the number of pixels, you're not going to see the issues with the edge. The chroma samples are closer together since there are no gaps in between the lines that interlace would cause. Progressive means better keys if you're shooting in a 4:2:0

[Michael Pruitt-Bruun] "also, 1080p? the project is destined for a WNET educational website, wherein our talent will present certain interactive elements. i'm not after progressive for the sense of motion, i'd rather it be smoother actually."

View any web video and examine the frame rate, It's either 30p, 25p (PAL), 24p. That's what the motion ends up as regardless of the source. Not only is there no point in shooting interlace for the web, you're actually creating all sorts of potential problems by doing that since deinterlace can be time consuming and can compromise quality. You really have no choice but a "progressive sense of motion" for web video.

The most important asset one can have is the ability to reason through your goals. Simple investigation such as downloading their videos would give you answers as to what they may expect.



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Michael Pruitt-Bruun
Re: Some more ex3 chroma key questions.
on May 1, 2011 at 4:28:21 pm

thanks for the info, Craig. i'm encouraged by the ex's ability to handle keying. and i know less about the technical aspects of the web than i do regarding compositing.


[Craig Seeman] "The most important asset one can have is the ability to reason through your goals. Simple investigation such as downloading their videos would give you answers as to what they may expect."

hmm, that's a bit condescending. beyond that, your second sentence there seems to be baseless, if not just too vague. if you'd care to expand, perhaps there's something buried that i haven't managed to unpack. this unit has never done this sort of video before. i'm not sure how downloading web video would provide information on camera settings that might make a compositor's life easier. there are so many stages and levels of compression that occur after the footage leaves my hands, but before it ends up in it's final form on someone's computer screen.

Michael


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Craig Seeman
Re: Some more ex3 chroma key questions.
on May 1, 2011 at 4:45:15 pm

[Michael Pruitt-Bruun] "hmm, that's a bit condescending"

Searching this forum using chroma key would have resulted in your finding previous threads with the answer including the Juan Martinez quote. Asking questions and expecting free consultation without first doing research is, itself, an issue when it comes to the time professionals devote to the forum.

The COW search function will often result in the answers you're looking for. Please do use it.

[Michael Pruitt-Bruun] "f you'd care to expand, perhaps there's something buried that i haven't managed to unpack."

Downloading the web video will show you the frame size, data rate, frame rate the client has used previously. You'd also find that web video is progressive frames.

I'm sorry if you don't like what I'm saying but the most important thing someone can learn is how to learn/investigate. Certainly some things are hard to find but the forum search would reveal chroma key with EX codec answer and the client's site would reveal the frame rate, size, and even the data rate they target.

Gamma curves is a bit harder to find but Alister Chapman's video explains the curves in the EX.



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Michael Pruitt-Bruun
Re: Some more ex3 chroma key questions.
on May 1, 2011 at 5:14:49 pm

[Craig Seeman] "Searching this forum using chroma key would have resulted in your finding previous threads with the answer including the Juan Martinez quote. Asking questions and expecting free consultation without first doing research is, itself, an issue when it comes to the time professionals devote to the forum.

The COW search function will often result in the answers you're looking for. Please do use it.

Downloading the web video will show you the frame size, data rate, frame rate the client has used previously. You'd also find that web video is progressive frames.

I'm sorry if you don't like what I'm saying but the most important thing someone can learn is how to learn/investigate. Certainly some things are hard to find but the forum search would reveal chroma key with EX codec answer and the client's site would reveal the frame rate, size, and even the data rate they target.

Gamma curves is a bit harder to find but Alister Chapman's video explains the curves in the EX."


i'm sorry if you felt i was wasting your time. regarding the search function, it is quite frequently useful. for some subjects, it can be difficult to narrow down the results to a useful or manageable scope. having asked a more specific question previously regarding the ex3 vs the '500 for the purposes of this shoot, i had been given an entirely different impression of the relative merits of the ex3's color space in the context of compositing. it appears that there are different views on the subject. i have met and spoken with Mr. Martinez in the past regarding certain issues i was having with my camera. as a spokesman for Sony, he plays a rather prominent role in the community. however i frequently find that those actually doing the work with the equipment are able to provide more specific and informative answers, based on their personal experience.

downloading web video allows me to see the final form of the video. as i am a cameraman with little experience with post production, the various processes the video undergoes, the numerous stages and iterations, are not something i normally deal with. the matter at hand concerns camera settings vis-a-vis those intermediary stages. the relationship that bears to the final product is beyond the scope of my knowledge, so it would be irresponsible for me to make assumptions based on what i can see only at the very beginning and very end of the process. this is precisely why i pose the question here, in this particular ex3 forum, where those with direct experience with the camera i own overlap with those who have a much better understanding of the compositing and post processes.

i have no problem with what you're saying. not personally. i just don't think it can be applied as blithely as you might.

regarding gamma curves, i appreciate the link. i am familiar with the fundamentals, it is the application that i am attempting to understand better. for many, myself included, the opportunity to consider these matters not as general descriptions but as a process of achieving a certain result in specific circumstances is the best way for them to develop a greater understanding, and extrapolate from there towards the general principles.

thanks again, Craig.


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Craig Seeman
Re: Some more ex3 chroma key questions.
on May 1, 2011 at 6:29:06 pm

[Michael Pruitt-Bruun] " i had been given an entirely different impression of the relative merits of the ex3's color space in the context of compositing. it appears that there are different views on the subject."

I'm not sure what the differing views are. EX shooting interlace to 4:2:0 can be problematic. Shooting progressive is much better. Shooting 4:2:2 HD-SDI to an Uncompressed codec or ProRes better still. It's just technical information. Mr. Martinez's post, without mentioning competitors, states that you can't look at color space independent of the proximity of the chroma samples to each other. Lines/pixels/samples packed close together aren't going to expose the issues as much as those farther apart. That's why he mentions HD involves a bit more than SD.

I believe his explanation is accurate because I've seen it first hand. The first time I keyed with the EX codec at 1080p I was surprised how clean the key was despite being 4:2:0. It might be comparable to shooting 4:2:2 with lower resolution (few lines, etc).

[Michael Pruitt-Bruun] "regarding gamma curves, i appreciate the link. i am familiar with the fundamentals, it is the application that i am attempting to understand better. for many, myself included"

Again, the background plate is the guide. Ultimately you want the curve to match that if you want the key to look natural. That's why it's hard to make a specific recommendation. You just need to know how to get there. The thing to be aware of is that EX 4:2:0 can't be pushed as far in post as 4:2;2. You can shoot "flat" and grade to match the background in post or you can try to get it as close as possible during the shoot. If you shoot Uncompressed 4:2:2 you may have a bit more room to grade in post. Without knowing your background plate it's hard to make a specific recommendation. Some people will do a test shoot to see how it'll all work out and make a PP to minimize post grade adjusting.

I should add that in some ways the web is far more forgiving. Keys that look fine on a website might be a horror on an HDTV and even more so on "the big screen."

I'm sorry I can't recommend a specific gamma setting beyond match the background plate. The close you can match it, the easier it will be for the people in post (short of shooting 4:2:2 so they can push things a lot if need be).

Generally you want to dial down detail and dial up frequency. Frequency setting adjusts width of the edge enhancement. The higher the setting more subtle the effect is. Someone suggested -20 for detail and +40 for frequency as an example for chroma keying. I believe others have suggested turning detail off entirely. I've seen STD 3 recommended as well as Cine 4. You should probably do a test but the above direction would be the idea. The diversity of opinion may well have had to do with shooting conditions, the subject, the background plate. That's why I stick to general statements such as dial down detail and the rest really depends. . . .



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Michael Pruitt-Bruun
Re: Some more ex3 chroma key questions.
on May 1, 2011 at 6:40:03 pm

thank you, Craig. i understand that there are variables, but you've given me a lot to work with. :-)

Michael


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Craig Seeman
Re: Some more ex3 chroma key questions.
on May 1, 2011 at 6:53:50 pm

You're welcome. I try to provide as much background detail as possible.

The sound bite version would be:
Dial down detail
Shoot Progressive
Match background plate gamma or allow for post grading to match

But doesn't tell you the why especially why 4:2:0 works as well as it does on the EX (but certainly would be more problematic on a typical HDV camera by comparison), so I include lots of explanation.

One really should learn the entire production/post production workflow. I actually learned the camera end by being an editor primarily. Way too much material coming in from DPs had problems because they didn't know the workflow. As an editor picking up a camera I had a huge experience seeing what was wrong so I was able to figure out how to get things right (or at least better).



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Bob Cole
Re: Some more ex3 chroma key questions.
on May 7, 2011 at 1:28:33 am

[Craig Seeman] "Progressive means better keys if you're shooting in a 4:2:0"

Thanks for that advice. Very timely. I'm totally amazed by the chroma-keying that I can do now with the EX1R, 1080p30. Practically effortless, and I'll be willing to use chroma-keys a lot more as a result.


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Michael Pruitt-Bruun
Re: Some more ex3 chroma key questions.
on May 1, 2011 at 4:13:28 pm

... and while we're at it, i'd love to hear some thoughts on gammas for this type of application. as it's a studio shoot, run-away highlights shouldn't be an issue. the cine gammas seem a little compressed, lacking in contrast. it's for a children's interactive website, it needs to pop. but if i put in too much contrast in the camera, will everything under 40 ire get crushed after down-rezzing, and being viewed on the web?


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Craig Seeman
Re: Some more ex3 chroma key questions.
on May 1, 2011 at 4:31:04 pm

Keep in mind to what extent you may need to grad in post and that your goal is likely to match the look of the background plate.

XDCAM EX Gamma Curves and Knee



XDCAM EX Color Matrix settings



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Michael Pruitt-Bruun
Re: Some more ex3 chroma key questions.
on May 1, 2011 at 5:45:05 pm

so, with a tip of the hat to Mr. Seeman, let me pose the question with the assumption that the ex3 suffers no significant disadvantage for its 4:2:0 color space in the context of chroma key compositing;

is it helpful to reduce detail in the ex3 when shooting for chroma key? if so, is there a particular interaction between the various detail settings that one should be aware of, or that might be helpful?

also, for material destined for the web, is it generally beneficial to favor lower-contrast gammas in view of the fact that web material will be significantly compressed and viewed on computer monitors? or will the lower-contrast gammas merely result in a flat picture?

thanks in advance.

Michael

(seaches done; "detail, chroma key", "detail, green screen" and "gamma, web")


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Craig Seeman
Re: Some more ex3 chroma key questions.
on May 1, 2011 at 6:35:01 pm

[Michael Pruitt-Bruun] "ex3 suffers no significant disadvantage for its 4:2:0 color space in the context of chroma key compositing;"

When shooting Progressive.

[Michael Pruitt-Bruun] "is it helpful to reduce detail in the ex3 when shooting for chroma key?"

Yes but some say lower detail and increase frequency (see my other post) and some say turn off detail entirely.

[Michael Pruitt-Bruun] "is it generally beneficial to favor lower-contrast gammas in view of the fact that web material will be significantly compressed and viewed on computer monitors? or will the lower-contrast gammas merely result in a flat picture?"

Computers can generally handle wider contrast than broadcast. Compression is about throwing away redundant data. It doesn't inherently change other aspects but certainly different tool and codecs can impact such things.



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Michael Pruitt-Bruun
Re: Some more ex3 chroma key questions.
on May 1, 2011 at 6:53:03 pm

the relationship between detail level and frequency is very helpful. i've been sitting in front of my field monitor, dialing various frequency settings up and down all morning. it gives me some sense of what it's doing, but i'm only guessing if that ultimately aids or hinders a key.

regarding contrast and gamma, i've seen some things i shot get absolutely butchered on the way to the web. flat and lifeless, while still suffering from banding, properly exposed skin gets pushed over the edge while shadows are crushed.

these are subjects i've been trying to gather more information on for some time. the gulf between production and post can be huge sometimes. i always ask, "do you have an editor on board yet, and if so... what can i do to make their job easier?" usually doesn't help. tests would be ideal, but again, not something people are willing to devote time to.


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Craig Seeman
Re: Some more ex3 chroma key questions.
on May 1, 2011 at 7:10:40 pm

[Michael Pruitt-Bruun] "regarding contrast and gamma, i've seen some things i shot get absolutely butchered on the way to the web. flat and lifeless, while still suffering from banding, properly exposed skin gets pushed over the edge while shadows are crushed."

There's nothing like bad compression to ruin good source. Way back when I was a youngling dubbing 2" video to new formats called VHS and Betamax, the chief engineer reminded us that we're actually the most important step in the process because it's what the client is going to on their home TV set.

When I eventually became a senior editor I insisted on meeting with the client and producer/director before production began. If you're on the production side you should explain to the client why this is important. It's also why the client has to take into account compression for web at the start of a project.

Actually your situation is a perfect example. There should be an editor or experienced post person helping you through this. That there isn't is why you're here. No fault to you but it should be a lesson given to the client. It they're ducking the cost of such consulting, they are walking into problems, which will cost them money or quality.



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Michael Pruitt-Bruun
Re: Some more ex3 chroma key questions.
on May 1, 2011 at 7:25:27 pm

yes, well... the client is a prominent PBS station. i have a good rapport with the unit, having worked with them for years, but there are certain institutional hurdles and restrictions on resources. it is only because i have worked with them so long that we have any hope of overcoming some of those hurdles and providing them with a more tailored product. people like DP's and editors are generally just pieces that get plugged into the existing structure for as short a time as possible. however the producer has indicated that she would like to have the compositor on set for the initial set up of our first shoot, so it is possible that we may get to do some tests and evaluations on the spot. but time and budgets are at a premium, so i'm trying to have my ducks in a row.


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Craig Seeman
Re: Some more ex3 chroma key questions.
on May 1, 2011 at 7:42:46 pm

[Michael Pruitt-Bruun] "the client is a prominent PBS station"

Having done stuff for PBS many years back, they are standards crazy (at least they were) so I'm surprised they're not buttoned down end to end. They were when I did post work that was to be aired on PBS.

[Michael Pruitt-Bruun] "he producer has indicated that she would like to have the compositor on set for the initial set up of our first shoot"

Ah, that sounds like PBS!

I'm actually surprised they'd be OK with EX 4:2:0 source. NanoFlash and KiProMini were designed with clients like them in mind.



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Michael Pruitt-Bruun
Re: Some more ex3 chroma key questions.
on May 1, 2011 at 7:48:32 pm

times have changed. some units are able to continue more or less as they have for years (American Masters, Nature), but most are expected to do a great deal more with a great deal less.

a huge amount of programming at this station is done on the hvx200. location and studio.


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