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GH4 with an external recorder vs Blackmagic for greenscreen?
  • Hi I just wondered what your thoughts were as regards GH4 with external recorders like Atomos v Blackmagic cameras for green screen. Would it be as effective at keying? One other possibly very naive question - is there any advantage in using sharper lenses for greenscreen? The Panasonic 12-35mm for example? Thanks a lot.

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  • For green screen resolution is very important. So, you better key in 4K and later downscale for delivery.

    Why you need external recorder?

  • Nothing beats raw in VFX. 2k raw över 4k h264 any day of the week. 4:2:0 can really ruin green screen material, no matter how good it is. But if you plan on mastering in 2k/FullHD, I say go with the native 4k in camera unless you got the Shogun that can actually record the 4K externally, other recorders so far is 1080p only.

    I don't know how much you know about shooting with green screen, but as usual: Keep the screen smooth, no wrinkles. Even lighting and keep your subject away from the green screen so you don't get any spill.

    In after effects I have found the primatte tools he best. CC also have few new tools compared to CS6 like an alpha cleaner and a better version of the refine edge tool. With compressed sources I usually split it upp to do different keying on different parts of the subject. Hair is one, the body is the other and combine the two layers for best key.

  • Thank you very much for both your replies and advice. I am a total noob as far as green screen goes. I haven't bought a GH4 yet I just wondered how good it would be for greenscreen. I was under the impression that an external recorder might mean it could output at a higher bit rate that would enable better keying (probably totally misunderstood that bit). If i just wanted the camera for greenscreen I guess the blackmagic option would be best but I need something a little more multi-purpose.

  • 2k raw över 4k h264 any day of the week.

    Do you have any actual tests?

  • Vitliy You know RAW is better for VFX and green screen YES its heavier but its better.

  • Vitliy You know RAW is better for VFX and green screen YES its heavier but its better.

    I did not asked about that I know. I asked for tests comparing 2K raw and very high bitrate 4K.

  • No tests, but actual work. Not allowed to share unfortunately. And GH4's 4K modes are 100 Mbps, which isn't really that high bitrate considering the resolution. If we split it in 4 (the same as 1080/2k) then it's 25 Mbps. Regular h264.

  • And GH4's 4K modes are 100 Mbps, which isn't really that high bitrate considering the resolution. If we split it in 4 (the same as 1080/2k) then it's 25 Mbps. Regular h264.

    It is quite high, and no, you can't "just split" it, it is more complex. For usual interviews and such (about 90% of all green screen that small firms and amateurs do) it is near loseless.

    And I think that such tests are necessary to do. Not so hard to make, really.

  • 10bit 422 1080 should key great. Mind you, if your green screen is poorly lit, all resolution and color space arguments don't amount to much, imho

  • The biggest problem in my experience hasn't been data rate, but color space. 4:2:0 is horrible to work with.

  • 422 color isn't ideal but it's doable, with proper filtering, and much better than any compressed format. 420 compressed, fuggetaboutit, that's amateur and will take a lot of effort to get decent results with. It's only advisable if you have no alternative. You'll spend effort just trying to get a decent, clean key, effort that could be spent on actually making the overall composite better.

    To answer the OP, no, the GH4 is not as good as or better than any Blackmagic camera for green screen, regardless of mode, Prores or RAW, but RAW is the way to go.

    edit: on top of shooting RAW, or at least 422, lens is going to be very critical. Even shooting RAW you could still get problematic edges if your lens suffers from chromatic effects. Here's where having a bland, clinical, "too sharp" lens, like, for instance, something Leica, really comes in handy. Something really modern will be better for shooting green screen than your classic lenses good for narrative and normal cinematography.

  • but RAW is the way to go.

    What software for keying work directly with raw data?

  • You debayer the RAW and work high precision linear.

  • You debayer the RAW and work high precision linear.

    Cool, in this case we must talk about 422 ProRes.

    And I still want to see good, well thought tests comparing 4K 420 and 2K 422 keying.

  • 422 Prores will still require special handling and filtering.

    The only thing well thought out, regarding 4K 420, is knowing it's not good, not advisable and only something you do if you have no other choice. It's a "make do" sort of deal, making the best of a bad situation.

    All of the problems with 420 1080P video are plainly evident in 420 4K imagery from the GH4. In fact the codec is even more harsh in a lot of sample imagery posted here and elsewhere than high-bit GH2 footage (highlights, particularly the blue channel). Scaling down 4K has already proven to retain macroblocking and other artifacts. There's no free lunch here. Dark, noisy edges at 4K are still going to look bad at 1080P the same way dark, bad edges done to 2K film scanned imagery still looks bad when viewed at 480P or even worse, once transferred to VHS.

    All those bad edges from opticals done in the '80s at ILM were effectively much higher than 4K resolution, given they did optical work with VistaVision plates. Even after all filtering from duplication and reduction for eventual broadcast or home video release there was absolutely no improvement to their quality. A similar principle applies here.

  • @BurnetRhoades

    Can you make tests or at least few illustrations showing issues, so everyone could understand?

  • I made a test using the GH3 internally recorded. Just guessing the GH4 externally recorded at 10 bits would be even better. If this can be achieved with a couple of clicks in Premiere I'm certain with a little love you could get good results in after effects. Check out all the detail that was kept in the fly away hairs by the crown. Didn't bother softening the key or messing with too many details but I really don't see why getting a decent key would be an issue. I've even done full body shots with green spill everywhere and keying it was no problem. It's just a matter of knowing your way around After Effects. As long as there is a difference in color there is a key to be had.

  • You can download the original ProRes file so you can see what I was referring to about the hair. Vimeo really mushes up the details. Even around the crown which I thought might be a problematic key, it was a breeze.

  • I think today's powerful keyer has made keying 4.2.0 footage much easier.

  • 60% of this video was shoot in front of a green screen using Gh3

  • @CarlosMorillo The hair is not too bad but I still see clearly green edges at the hands and the forearms

    image

  • @peaceonearth You are right. That can easily be corrected with a couple more clicks. The point was to show how easy is to key out 4:2:0 footage from a GH3 with it's compressed internal code and minimal effort by color picking the background. The ultra keyer has settings for removing spill from the edges adjusting saturation of color being keyed and to choke/soften the matte etc. The GH4 recorded to 10 bits in 4K uncompressed should key more cleanly.

  • I been doing digital keying since the video cube ;) the most important things to remember are object isolation against the background to avoid the spill, separate illuminations to the background and the subject, avoid shadow casting and keep a plain illumination on the background. Modern software make to easy to do Chroma Key, mainly digital compositing software (After effects, Nuke, etc..) thanks to better tools to do this. The image from the GH4 with a external recorder at 10Bit definitive will help, thanks to the improved resolution and additional color space, RAW data i don't think it will help too much if the first rules are not accomplished. My two cents.

  • I re-upped the video and with just 2 more clicks removed some of that green edging. Again this is not to say keying 4:2:0 footage is optimal but simply to say it's not nearly as big a nightmare as it's being made out to be.

  • @CarlosMorillo awesome for 4:2:0, corrected result was worth the effort. Well done!