Chroma key experiences, workflow,tips, etc

virgilr

So I've trawled and searched for GH2 user experiences for chroma key work here at PV, and it seems to be spattered and scattered around the boards. I have access to a GH2 that will be used on some upcoming projects, and I'm putting this here for anybody to share their best patch - workflow - tips in terms of pulling the best keys possible using the GH2.

Obviously lighting and setup are critical to pulling good keys, and I know that many may be tempted to say "try it and see"- which I'm definitely willing to do! I'm just trying to shortcut a bit to the best possible starting point I can before delving into the process on my own.

Any sample footage would also be greatly appreciated!

Ralph_B

Here's my expereience:

1) With the GH2, greenscreen will give better results than bluescreen. 2) Shoot at ISO 160. You want as little noise as possible in the picture. 3) Set sharpness to -2.

I use Sanity 5 as my patch, but I've pulled execellent keys even using the stock settings.

andyharris

I use Sedna-A and three lights on the background to avoid shadows in the creases. Some really good bulldog clips helped.

What really helps me is the two sliders that are revealed under 'Colour' in the FCPx chroma key. I can solve most problems by moving them both to 50%. Normally I scan over the clip first, if there is a problem I increase the value of the sliders as little as possible until I get a clean key.

Example:

virgilr

Thank you both for your insights! Good tip on the screen lighting, @andyharris. @Ralph_b- thanks for the information regarding both patched and stock settings. So, it doesn't seem to make a whole lot of difference, then, in terms of noise and "key-able" footage if a particular patch is used?

A couple quick questions for both of you- do you find you have to tweak your keyer settings strongly due to issues with the footage- in such a manner that you start to see erosion of details in the keyed content (such as fine hair detail, etc)?

Secondly- have either of you ever used 5DtoRGB transcodes of your footage, or do you use the footage straight from the MTS files?

Again, thanks to both of you!

Ralph_B

I key straight from the MTS files and it works great. But I'm on PC and don't have any Mac issues to deal with. There's really nothing special about GH2 footage as far as keying goes. It's similar to any good 3-chip video camera. Have fun!

virgilr

@Ralph_B Good to know keying the native format files works out well. I had read that 5DtoRGB, in it's process of YUV->RGB conversion, does some very nice edge subsampling/smoothing that can help keying difficult subjects (lots of fine hair, etc).

I appreciate all replies here!

endotoxic

5d to rgb, convert file of color 4:2:0 to proress 4:2:2 HQ.

perfect key.

virgilr

@endotoxic- have you found it be helpful in converting with 5DtoRGB?

endotoxic

@virgilr yes, better image, grate edge subsampling smoothin.

andyharris

@virgilr For me the erosion of fine hair details happens far more when the background is not evenly lit. I can see when trying to lose a particularly nasty crease starts to impede on image quality. Luma and Chroma sliders past about 70% will start to eat into quality.

When this has happened, I've used the blade tool to cut the footage into sections, then crop as far in as possible, then key whatever is left.

I used to import the MTS files directly into FCPx but the latest version is not liking the high bitrate patches, so at the moment they are going through iCamera Wrapper, this doesn't affect the keying at all.

Currently I'm borrowing a pair of LED replacements for the typical 500x500mm office lights. These are powered by 48V and are basically a 500x500x8mm form factor. The light they create is so soft it really helps deal with backdrop creases and folds. Unfortunately the CRI on these is about 80 so they are not good enough to be used as main lights.

willianaleman

endotoxic wrote: "5d to rgb, convert file of color 4:2:0 to proress 4:2:2 HQ. perfect key."

Since the 4:2:2 color space is not contained in the original footage, I would like to know what someone is getting from the conversion of 4:2:0 to 4:2:2 HQ for keying purpose?

virgilr

@willianaleman- That much is true in regards to the color space conversion- 5d to rgb doesn't magically create bit depth that doesn't exist! However, from what I've read on their website, the conversion process from YUV->RGB is more precise than that done by most NLE's or effects packages, so you get a cleaner conversion, and it does some edge smoothing in the process.

I don't have any GH2 footage to test with at this point, but I should have a chance in December at some point. I'm going to try and do some testing with various firmware patches, as well as using 5d to rgb, and see what those differences are (in some kind of controlled way).

Stray

@willianaleman Yeah, you're right, its not actually any easier to pull a key from footage pushed into 4:2:2 from 4:2:0. Though some seem to perceive it as easier. Although its still all down to how your platform interprets your MTS file in colour terms (which is why most FCP users use 5DtoRGB or neoscene or whatever). Those issues (to 5DtoRGB or not to 5DtoRGB) is a recurring flamewar here however.

The only perfect keys exist in product demos ;). Fixing fine detail loss, key spill and such, there are many methods you can use to do those and other kinds of fixes. Which can be different dependant on each unique green screen shot. There are no perfect keys, you should expect to use any number of techniques such as mattes and multiple key pulling. Even using wholly different keying software in conjunction with each other, for example sometimes using a colour key on a channel that gives you the most contrast (which could be the red or blue channel, or even a luminance key) just to fix the edges of a persons hair (and cut out the green spill from the screen you get from fine hair) and then compositing with the green pulled key to get a good matte. Edit : Or, more likely, composing the multiplied result from any number of keys and rotos, into one good foreground and composing your alpha matte seperately (though mostly taking the max pixel values from the seperate alphas).

Theres loads of approaches you can take. As @andyharris says though, Its still a shedload easier however if your screen and scene were well lit, thats the main prep that counts.

virgilr

There was a comment made in a clip on a DIY site about lighting (that didn't have to do with keying, I can't remember the site) by the narrator that he used white backdrops for keying. I find that interesting, but problematic at many levels to say the least!

Although it seems that some roto/multi-matte work is going to be the case with almost any keying job- so I guess rotoing a highlight in the "keep" portion of a key with a white backdrop wouldn't be the end of the world. Goes to show you everyone has a different approach!

sam_stickland

I guess there aren't going to be any problems with green-spill with a white background! But man, it sounds like a lot of roto!

Stray

I've never tried it, but I've pulled elements from a white background before. To me a white key sounds like an absolute nightmare, you're going to have to soften/sort your edges out an awful lot before compositing. Pulling from white by keying the blue channel can work out okay though, but white spill is going to give the same, if not more, problems for you as green spill (its going to 'pop' out more I think). I could be wrong thinking here though, and theres something fundamental I'm missing.

paulo_teixeira

Yes Chroma Key can seam overwhelming at first. When I decided to fool around with the Ultra Key feature of Premiere CS5 (because I know the kid was into green screen and I wanted to see how I would do fooling around with a sample. The kid on the other hand uses Final Cut for his green screen projects), I immediately thought of doing a music video using mostly green screen footage when I obviously didn't have much experience so I took a very big gamble. Here is that video:

That is the kid's YouTube channel. The video is also on my Vimeo channel along with "Making of" information in the description. I'll re copy it here:

Michael is into green work and so I said I should make a music video using green screen. One idea to somehow make it unique is to clone them. On the day of shooting, I just allowed the kids to act anyway they want so I wasn't really directing and I think they did good. After shooting, we all put a bunch of ideas together to think about how the final piece will look and here it is.

It was shot with the Panasonic GH2 using the 20mm lens. The green screen was not anything fancy and the florescent lighting came from TubeTape. It was edited in Premiere Pro CS5 using Ultra Key rather than After Effects. Besides the drums scenes which was a bit chaotic with the shadows on the floor and the symbols reflecting the green, The Ultra Keyer did pretty good considering it was a cheap green material that we used and because we were shooting in a tight place, the lighting wasn't in the best spots but it still ended up decent. I used PhotoShop for the night scene. The swimming scenes were shot with the SD600 and the other real life scenes as well as the flying scenes were shot with the Canon S95. The flying scenes were edited by Michael and then inserted into the video.

This whole idea was just for fun and because of it, I've become pretty good using the Ultra Key feature in CS5. It's my first big project using Ultra Key. I've done concert videos and even edited multi cam concert videos but this is the first time making a traditional music video. I expect to be much better next time.

vimeo.com/31986852

Anyway, when I shot this, the GH2 was not hacked and I used straight MTS files. Something that helps a lot when doing keys are using masks or crops. In the case of Premiere Pro, I used the "Garbage Matte". This helped a lot because some parts of the green screen wasn't that great and it wasn't lit in the best way because of how tight the location we shot this in.

virgilr

@paulo_teixeira - thank you for your post! I had seen your video a while back when trawling the net for chroma key projects done with the gh2. Great work for a first-time effort!

My first-time effort was, alas, not shot with a GH2. In fact, after the project was completed, my friend who produced the film purchased a GH2 after we discussed various options for future film projects, so I now have one at my disposal, but haven't had any time to work with it being a self-employed web developer. Hopefully next year some smaller projects can be realized with the GH2- I'm terribly excited to use it, what with an adapter for all my Pentax K-mount manual primes!

So my first ever production to be involved in was shot on a JVC consumer HDV cam (can't remember the model!), which I would never, NEVER do again! A 40 minute film that was entirely composited, every last minute. The film is titled "Lovleighton Manor", was written by my wife's best friend, and we got together with with the best cast we could put together over several weekends scattered through 2011 to shoot the piece. Post started in winter 2011, and final project was done in April this year. My friend and his wife produced the film. I performed all post (audio and video) and worked on the initial editing together with my friend and his wife.

I learned quickly from all the mistakes made in the shooting of the piece, and have to say we're proud that we were able to pull together a decent film that held together despite tons of screw-ups in putting together a chroma key project. All keying was done in Ae with Keylight- some scenes had 5-8 layers of footage (rotoscoped, garbage matted key layers to deal with crap screen lighting, etc), and to top it all off, yep, we shot on a BLUE SCREEN with a consumer HDV cam - it was done with intent since some of the costumes were green, and some scenes had flowers with greenery in them. I'm sure those who have dealt with bluescreen HDV tape compressed footage know what a nightmare that blue channel is to deal with.

The end scene was alot of fun, actually- all the shadows were generated by projecting shadows onto 3d planes in Ae- it was great to add a touch of realism without having to do full 3d rendering!

I threw myself into this project, wanting to get the best possible result out of it for all the effort put into it by my friend, his wife, my wife- everyone put in such great work on this, from the writing to the costumes to the performances. I really feel like it stands up as a decent piece of independent film making.

Keying unfortunately had to go the "lowest common denominator route", where keys were heavily eroded due to very poor screen lighting and the evil beast, wrinkled screen fabric. So I wasn't able to do this in a way that was technically perfect, but everyone who is a consumer (not being privy to the fact the entire film was composited) didn't seem to notice or care that much, and that was huge relief for me- I didn't want all the work that went into this to look so fake that an audience couldn't enjoy the film.

So, moving forward with the GH2, I'm so glad to have a space where others are sharing their experiences with keying- I found the whole process of film making from beginning to end inspiring- hitting the right notes in my skills and passion. I wanna keep going!

Here's the url for the film- it is 40 minutes long, btw, but watch if you wish when you can. We're all proud of it!

vimeo.com/40420578

virgilr

Just wanted to say, I couldn't embed the video above since I'm not in control of the vimeo account and my friend hasn't enabled embedding on the clip.

Just wondering if it would be worth it to look for a good buy on a used GH1, since it has MJPEG at 4:2:2 compression- I know it's limited to 720p- after reading a bit on EOSHD it looks like the mode isn't as "clean" as AVHCD, but if you're shooting in a controlled environment with studio lighting, etc, wondering if it would be any better having 4:2:2 footage for keying?

Thoughts, anybody?

Jspatz

I don't see dramatically better keying from my D800E and Ninja 2 over a hacked GH2 and the GH2 has slightly better detail and less moire. Even lighting and very green background material seem to make more difference.

paulo_teixeira

virgilr, thanks for the video. It has a good story.

It's definitely a pain working with many layers and that's how my video was as well and not to mention I had to keep on resizing the background photo and the kids for each scene. One things for sure is that not having a 100% perfectly good green screen set up for your first video does help you learn more about adjusting the key settings. I think if my keys were much easier, I wouldn't have had as much experience as I did. I had to basically look up instructions online while editing this piece at the same time to see all the best tricks to make my keys look as good as it can be. Still a little pissed I couldn't get the cymbals to key properly. I found out online that I wasn't the only one who has trouble.

I have CS5 and I'm assuming the key features of Premiere and After Effects CS6 might be better so if it is, perhaps your team will want to upgrade to CS6 if possible for your next key project if it's not already. One thing I like about Ultra is not needing to go from Premiere to After Effects so that's worth a try at least for experimental purposes.

virgilr

@Jspatz- That's good to know! I think, unless one goes with a real cinema camera that outputs true 4:2:2 10 bit in some format (most likely hdmi capture) then we're all on fairly even ground in terms of camera tech. All the tenets of chroma-key filming are what are crucial to pulling good keys! It's truly garbage in/ garbage out if not.

@paulo_teixeira - Believe me, I would have much preferred to have keyed with ultra key in Pr (we used CS5 as well on the project). However what needed to be done for the film was best to do all in Ae: all backgrounds were 3d renders, and getting DOF was done with DOF maps baked into the background 3d rendered images- can't do that in Pr! As well, I re-lit much of the footage with Ae 3d lights, created spill layers in Ae, animated masks in Ae, created projected shadows from 3d lights, etc- none of this could have been done in Pr, so I had no choice really.

AFAIK, there are no grand improvements in the keying tools in CS6 in Ae. However there is SO much more power in Ae for complex compositing projects, and I'm learning constantly as well! We all keep learning, every day... ;-)

virgilr

Right! So, ran a quick chroma-key test today. Details:

AN BOOM! 24L ISO 160 Cloudy WB Smooth, -2 across the board

Lens: pentax k 30mm f/2.8 1/50 second f/3.4 (unmarked stopped on lens between 2.8 and 4)

Lighting: Natural light for key, 1 CFL to light green material, halogen desk lamp used for back light on subject.

Keyed in Ae with Keylight. Only 1 instance of Keylight used, (no multi-keys, etc- not needed here).

I'm very happy. Blond hair! Good key!! No need for special pre-processing to pull a good key. Impressed using an Intra codec. Setting up the key was quite straight-forward: gotta love Keylights edge correction tools, they make all the difference.

Note that noise in the red background was introduced from the crappy conversion down to H.264, then bit-rate hammer that Vimeo adds....

Mark_the_Harp

@virgilr So the other one on Vimeo - your chroma Key with the live actor? That's really chroma key? That's amazing!

virgilr

All right- this is MUCH better. Live actor (well, me!)- with some decent controlled lighting this time instead of lazy no lighting with daylight from a window. @Mark_the_Harp, the version you saw wasn't that great- well now I've updated it like 4 times, so not sure what you saw... anyways as well I really needed to shave! Bad thing when you're self-employed, you sometimes forget little things like that... ;-)

I think I'll post the Vimeo version- YouTube seemed not to have liked the color profile in the clip? Looks too washed out (which I usually don't mind, but YouTube took it too far).

Details:

AN BOOM! 24L ISO 200 Standard color profile, -2 across the board except for NR at 0

Lens: pentax m 50mm f/1.4.

Shutter:1/50 second. Aperture: f/4.0

Lighting: two 5000k CFL's on two stands for green screen, 2 CFL's in one stand for key light.

Keyed in Ae with Keylight. Only 1 instance of Keylight used, (no multi-keys, etc- not needed here). Plate is photo I took at Upper Canada Village. Grading with Color Finesse.

I REALLY don't get what Drew at Drewnetwork was going on about- albeit I'm using an intra patch, he just trashes keying gh2 footage. (Link to his trashing video: youtube.com/watch?v=Unb7aUOH4UM).

I think this holds up pretty well- it isn't perfect by any means! But it's quite good for 8 bit 4:2:0 footage. I have to say that keying with ultra keyer in Premiere hasn't been for me the best way to go- yes, keylight is more complex, but man, you can so fine tune your key.

vicharris

@virgilr Wow, looks great man! Can't ask for anything more than that from this camera. Well done. The out of focus background really helps. Did you throw some grain on there too?

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