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GH2 HDMI output 4:2:0 or 4:2:2 with garbled chroma timing
  • For over a year, there have been contrasting reports. Can @Vitaliy_kesselev give a final answer ? Is the GH2 HDMI output a YCbCr 8bit 4:2:0 or a YCbCr 8bit 4:2:2 with timing and cadence issues ?

    On every thread, the opinions seem to change between 4:2:0 and 4:2:2.

  • 15 Replies sorted by
  • If no one can tell, what's point to know it ?

  • Because its worth picking up a recorder and testing it if its definitely 4:2:2. The dude at Marvels film is sure its 4:2:2 and that there is additional shadow detail.

    Its a big effort to test it, so I am making sure I am not reinventing the wheel.

    The difference will show up during grading, and greenscreening. Especially in greenscreening with reduced color bleed.

  • @zcream

    Search for AviSynth solution. And read it carefully.

  • My tests with some of the best Driftwood patches and an external recorder (Ninja, 25p, well, actually PsF) by using difference images showed such minor nuances that it seems to be 4:2:0 and that external recording doesn't make much sense with a hacked GH2.

  • I read this part earlier.

    IS THE HDMI OUTPUT 4.2.2 ?

    The question of whether the HDMI output is 4.2.2 constantly comes up. The fact is, nobody knows because the chroma is so mangled up. What we know for certain is that after applying the Chroma Fix, we have a clean, uncompressed 4.2.0 picture. As a practical matter, this is the best way to think of it.

    However, the 4:2:2 reference still keeps on turning up. Here is Marvels film blog.

    The HDMI signal from the has been described by Barry Green as “screwed up 4:2:0″, but other tests by Jorgen Escher shows that it’s really 4:2:2 that has been deliberately crippled by Panasonic to make the camera less interesting for professional vido use. This “cripple” mainly exists of timing disturbances, applied to both the video timing (“field cadence”) as well as the timing of the separate chroma channels. Despite everything, HDMI recording eclipses the AVCHD recording in many ways, such as:

    • More detail in shadows (less muddy blacks)
    • No compression artifacts
    • Better overall detail
    • Better color rendition
    • Different noise pattern (finer)
    • Less pronounced solarization (a.k.a. color-banding -> yes, this is an 8 bit camera)
  • Images?

  • How come you guys are so sure that it is YCbCr and not RGB? I've read the whole topic but can't find any information on that (see this other thread)

  • Because any kind of chroma subsampling on the signal means it's not in RGB color space. It can be converted to RGB color space with more or less losses depending on the subsampling scheme, but it's still not RGB to begin with.

    And most if not all external video recorder won't accept a signal who is not in YCbCr space (like a computer monitor output for instance).

  • @nomad Exactly the problem. I have no images. So far its only been hearsay.

  • @zcream Do you have a device to record the HDMI signal? If you do, you can run your own tests. If not, it's probably not worth the effort and expense to get one. The hacked patches bring the quality so close, it just doesn't make any difference. If you think there's some advantage to using HDMI for greenscreen work, forget it. I have done extensive tests with this. First, if you don't process the HDMI footage with Avisynth and use the Chroma fix, the HDMI picture will key WORSE than the onboard footage. If you apply the Chroma fix, then it will key the same as the onboard footage. In no case, will it ever key better.

  • @duch most recorders (like Atomos Ninja) do support HDMI RGB input, as of specs all HDMI devices must support the sRGB color space at 8 bits per component (source: HDMI specs).

    I am with you on the part that chroma subsampling has for sure been done, but why are you so sure that converting to RGB is not done by the HDMI output-unit of the GH2 itself?

  • I'm pretty sure the chroma subsampled signal is not converted back to RGB as it won't make any sense (and I don't know if the GH2 has enough processing power to do a double conversion).

    On the other hand, digital still camera are RGB pieces of hardware to begin with, so it might make sense to send non chroma subsampled signal to the HDMI out.

    Regarding recorders, AJA Ki Pro and Ki Pro Mini do not support RGB over HDMI. Tried and confirmed by AJA themselves. As those recorders reads the HDMI out from the GH2 juste fine, it is my understanding that the signal on this output is not RGB.

  • I am receiving a GH2 and AJA Kona LHi next week. The Kona card supports many video modes over hdmi so I will try and capture a signal and do some pixel peeping.

  • Heeey guys!

    Sorry for bringing this old topic up! But I was wondering, especially to @vicx, have you've had any luck with your experiment??? What were the results or your outcome? :D

  • I'm fairly sure the HDMI out is 8bit 4:2:0. The chroma sampling in Y Cr Cb happen very early in the signal chain and are handled by hardware not software. The resulting signal is compressed into the recording format (AVCHD) and also sent to the HDMI out.