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Chroma key experiences, workflow,tips, etc
  • virgilrvirgilr

    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!

  • 44 Replies sorted by
  • MikeLinnMikeLinn

  • nekoneko

    Hi everyone, I'm new to this forum and a brand-new GH2 owner (after some canon dslr experience). I am very interested in chromakeying and found this thread to be very helpful, but there are still some things I would like to understand better, for example the chroma subsampling issue: I know there are matrixes that "mimic" 444, but is this specific process an advantage when dealing with greenscreen? Or is it just meant for 'real world' shots? Also, I know of the 'earlier' ultra-high bitrate intraframe settings (176Mb and 244Mb) and in my imagination they would be a very good choice for keying since we're dealing with 1GOP at around 1MB per frame (I have ordered the 64GB 95MB/s SanDisk sdxc card). But I could be wrong and newer settings are actually better suited. I would love to hear your thoughts on this, thanks so much!

  • Mark_the_HarpMark_the_Harp

    Sorry if this isn't done on the GH2 but it's a FAB exposition of how greenscreen is used in the movies - often for stuff I'd never have assumed was greenscreen, such as street scenes. Suppose it makes sense, though, to be able to do stuff in the middle of a city with spending gazillions in back-handers!!!

  • virgilrvirgilr

    Vitaly- Thanks for the video links! I know there was a thread concerning green screen and compositing- I had just wanted to start a thread that dealt with different users' experiences using the GH2 for chroma-key work.

    Thanks to all that have contributed to this thread!

  • Vitaliy_KiselevVitaliy_Kiselev

  • Vitaliy_KiselevVitaliy_Kiselev

    Other topic on it

    http://www.personal-view.com/talks/discussion/1737/optimizing-your-greenscreen-shots-when-shooting-with-the-gh2

  • BrokenbarrelproBrokenbarrelpro

    @virgilr - I've personally had very good results from chroma keying with the GH2 and a green screen (so much better than the old HDV chromakeying!!). My latest is here:

    This was using Driftwood's VY Canis Majoris 'Green Screen matrix setting' at 720P 50fps, Keyed in After Effects using Primatte Keyer, Neat Video denoise plugin, colour corrected, then adjustment layers with unsharp masks and sharpen effects. The denoise plugin really cleans up the alpha channel; I will not chromakey without it, and you can always bring the image detail back with the sharpen +unsharpe marks.

    Earlier work (my first GH2 chroma key) that didn't look so good:

    This video below was also using Driftwood's VY Canis Majoris 'Green Screen matrix setting' at 720P 50fps, but not as good an outcome as the latest video:

  • Mark_the_HarpMark_the_Harp

    Exactly - so light / expose the shot for keying so everything is slightly above the background black (and match the lighting / direction so it works when inserted) so i can make the black bg transparent, and then adjust that footage down (or whatever) so it matches in levels etc with the "backplate" (which I assume means the eventual background in the final scene?) - all makes sense. I'll give it a go! The background in this case of course, being on real life a miniature model. Could be fun!

  • virgilrvirgilr

    @Mark_the_Harp - that was a brilliant idea to shoot against black! I would try and two-point light your subject, keeping a tonal balance that matches your backplate in terms of light source/shadows, yet avoid any exposure in your subject that is 1/2 stop away from your backplate. Then you can post the keyed footage to get a better match to your backplate in terms of intensity, color balance, etc. I think you'll wind up in a mess if you try to light the actual footage to match your plate without some post to get it closer. Just my $.02

  • Mark_the_HarpMark_the_Harp

    Yes - and I had a go at shooting against black and essentially doing a luma key. That seems to work much better. Still going to be tricky as obviously the lighting needs to match the scene to work convincingly, and also ensuring that none of the levels of the "wanted" image are anything like the background black. So will keep experimenting but luma keying does give me a very crisp edge to play with.

  • fredfred27fredfred27

    That is a tough one! My guess is that the speed of vibration would be too fast to stop the blur. Say you pluck A 440. The sting would complete a full cycle in 1/400s. Even with a shutter speed of 1/400s, the string would still completely be blurred. Each frame would capture an entire cycle. Good luck!

  • Mark_the_HarpMark_the_Harp

    I was going to key some harp shots but just remembered why I've had problems in the past - the vibrating strings have always caused me trouble in trying to key them. I think it's because you see through them (nothing behind, unlike most other string instruments) and the strings blur as they vibrate and that blur changes, moment to moment, so the video levels aren't consistent. Maybe I'll try shooting at a high shutter speed in very good light, and get clean images of the strings to make it easier to remove the background then somehow add shutter blur back to the keyed image of the harp after the background has been removed (if that makes sense) to have the strings blurred again.

    Or perhaps I'll shoot against a dark background and experiment with what is the best way to overlay the harp image.

  • virgilrvirgilr

    @under1979 - Unfortunately not me! Not sure if extra DR would help in chroma keying- usually the shots are done in very controlled lighting conditions where maybe 4-6 stops of dynamic range is captured. Obviously it would be ideal to shoot with the BMCC - I'd love to key some raw footage at 4:4:4!

    I know that there would be other shots than chroma key shots on your project and you may require the extended DR of the GH3, as well as matching footage, etc so I can see why your asking.

  • under1979under1979

    Hi there.

    I was supposed to shoot some chroma shots for a shortfilm by end of January with BMCC. It doesn't seem possible due to the BMCC delays and bla bla bla...

    Now, i'm considering to get a GH3 for this task. Has anybody experienced chroma tests with GH3. I can do it with my current hacked GH2 but i NEED this extra DR from GH3.... Another option would D800 but, honestly i rather stick with my panny M4/3 lenses... Anyone?

  • virgilrvirgilr

    Here's a great series of tutorials on getting started with keylight from creative cow- not every detail is covered, but it gives you a sense of how keylight works, and all the f%^&*#'ing problems that keying poses and how to try and deal with them!

    http://library.creativecow.net/search.php?q=Multi-layer+Keying+in+After+Effects

    Check out the Multi-layer Keying in After Effects series by Andrew Davis.

  • virgilrvirgilr

    @vicharris- yeah, it's just that easy... ;-) I'd say I spent ~3 hours total, from keying to grading. No tricks on the background plate. Most of the time is keying!

    @Mark_the_Harp - I'm glad the thread is useful to someone! Good luck on your project, and yep, I've seen the hollywoodcamerawork plates, footage, etc. My friend bought their director series DVD's- those guys are awesome, I love their commitment to the art and craft of film making, and sharing it!

    One thing I'm learning with keying- it'll never, ever be perfect. There is always some compromise. THE MOST IMPORTANT THING is lighting your green screen properly! This was simple- I just stuck a piece of green poster board bought at the dollar store to the wall and set up the shot. But even then, I still had some shadow on the screen because I didn't have enough light on the screen vs my talent lighting. I also had spill since I didn't have a large enough green backdrop to put the talent far enough away from the screen to avoid spill.

    Keylight takes some working with, that's for sure- it's not a one-click solution. I'm sure there are some other fantastic keying tools out there. both for Ae and in other packages. I just think it's fantastic that it's part of the Ae package! It does do a great job, but take your time and don't get too frustrated. I did a whole lot of resetting the plugin when starting out (still do!) because there is very much a rabbit hole effect when tweaking keys- you think you're on the right path, you have a ton of tools and options to fix problems, but whenever you have to start making extreme adjustments it's best to take a close look at the footage for problems or start over and think your way through.

    Thanks to both you guys for your awesome comments!

  • Mark_the_HarpMark_the_Harp

    Hi guys - have you come across this resource? Not so much for GH2 as it's already-shot footage - but for experimenting with keying / tracking / matchmoving (there are two pages of different ones - see the link at the bottom of the first page for more: http://www.hollywoodcamerawork.us/greenscreenplates.html

    They're all free.

    And back to the actual topic, which is GH2 for Chroma-Key, while I'm not totally into Keying I've found this discussion really helpful as I want to put together a music performance keyed into a miniature Christmas scene - for fun really and also to get my head around After Effects a bit more. Keylight really seems to rock - given I've never had that much luck keying in Sony Vegas.

  • vicharrisvicharris

    It's just that easy, eh? :)

  • virgilrvirgilr

    @vicharris Thanks! Well, I put in a back plate that would be fitting the type of shot and focal length/aperture that I was shooting at.

    Yep, I threw a bit of grain in to just help "sell" the shot- not to cover any keying garbage! I can post just the keyed footage over a solid colored background, but that's just boring... ;) It's a very clean key!

  • vicharrisvicharris

    @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?

  • virgilrvirgilr

    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.

  • Mark_the_HarpMark_the_Harp

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

  • virgilrvirgilr

    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....

  • virgilrvirgilr

    @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... ;-)

  • paulo_teixeirapaulo_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.

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