Common knowledge tells us that codec and compression are two of the most important factors (after lighting, of course) when it comes to green screen work and being able to pull a quality key from your source footage. Anybody who has ever had the opportunity to shoot green screens both with DSLRs and higher quality cameras with more robust codecs can attest to the fact that it's significantly easier to pull a key from the latter. However, seeing as the GH4 keeps blowing past people's expectations, it was only a matter of time before we started to see green screen comparisons to cameras with better internal codecs. The fine folks at Video Alchemy performed one such test recently, and ran the GH4 up against the BMCC's ProRes and CinemaDNG. The results are surprising, to say the least.
Before we get to the comparison video, we should talk about what the expectations would be for a test of this nature. Taking the GH4's 8-bit 4:2:0 4K output and running it up against the 1080p ProRes 4:2:2 and the 2.5K CinemaDNG from the Blackmagic Cinema Camera seems like a bit of a mismatch, especially considering that the BMCC is an incredibly sharp camera in its own right, but with far superior codecs. Based on this alone, it would be safe to assume that the BMCC would outperform the GH4, even despite the fact that it's not a 4K camera.
With that in mind, here's the test from Video Alchemy.
Right off the bat, it's clear that the GH4 holds an advantage in terms of overall image detail, which should come as no surprise considering that it almost holds up to the EPIC (just in terms of detail). However, what's really surprising is that the GH4 looks to pull a slightly better key than either of the BMCC examples, despite the fact that the 8-bit codec should be struggling around the edges of that afro. It's hard to say that the GH4 wins this battle outright because the key is slightly softer around the edges than either of the BMCC examples. However, you can't argue with the fact that the GH4 example looks absolutely fantastic.
Of course, the BMCC was no slouch in this competition either, and both the ProRes 422 and CinemaDNG pulled fairly solid keys with little work. Ultimately, both of these cameras are going to be viable options if you intend to shoot against a green screen with any frequency. Considering they're both in the same price range, the decision between the GH4 and BMCC should come down to whether or not you need 4K output or RAW versatility, and not the performance of the internal codecs.
What do you guys think of this test? Are you surprised that the GH4 performs so well despite its inferior 8-bit codec?