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Does the GH3 output 4:2:2 or 4:4:4 video from it's HDMI?
  • tommydog35tommydog35

    Does the GH3 output 4:2:2 or 4:4:4 video from it's HDMI? I can't find this in Panasonic's technical specifications anywhere. Does anyone know?

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  • MikeLinnMikeLinn

    You better check GH3 topic for this. It can be 422, but I doubt it.

  • tommydog35tommydog35

    sorry but I don't understand what you mean. For HD I thought there were only 2 approved standards for HDMI 4:2:2 or 4:4:4

  • thetricksterthetrickster

    The GH3 is 8 Bit 4:2:2 via the HDMI port.

  • tommydog35tommydog35

    thanks thetrickster for confirming 4:2:2 - this is what I thought. Do you know the mbps what the HDMI outputs?

    One thing that was confusing me was that many people say the GH3 only outputs 4:2:0 from it's HDMI. See these links:

    http://luminous-landscape.com/panasonic-gh3-field-review/ "One of the GH3’s capabilities will perk up the ears (and eyes) of serious videographers is that the camera puts out a clean recordable HDMI signal (4:2:0 colour space and in 8 bit). One could have wished for 4:2:2 and 10 bit, but not at this price point, I suppose."

    http://www.imaging-resource.com/PRODS/panasonic-gh3/panasonic-gh3VIDEO.HTM "There are no specifications in the GH3 manual as to the quality level of the uncompressed HDMI signal, however we've seen reports stating that it is an 8-bit 4:2:0 signal, which is not as high quality as 4:2:2"

    There was even some comments on personal view regarding this: http://www.personal-view.com/talks/discussion/4733/official-panasonic-gh3-topic-series-2/p15

    I don't understand what people are talking about with regards to 4:2:0, as research tells me that this is not even a recognized HDMI standard for HD video. Plus I just got an email from Panasonic confirming that the GH3 outputs 4:2:2 from the HDMI, so what's all this talk about 4:2:0 ?

  • davedvdavedv

    HDMI 1.4 and earlier only allowed 4:2:2 and 4:4:4 chroma subsampling formats. Support for 4:2:0 wasn't added until HDMI 2.0. Since the GH3 doesn't support HDMI 2.0, it's HDMI output format would have to be at least 4:2:2.

    Having said that, just because the HDMI signal format is 4:2:2 is no guarantee that there is actually that much color information available. In principle, a 4:2:2 signal has twice the vertical color resolution of a 4:2:0 signal. However, it's pretty easy to take a 4:2:0 signal and copy the chroma samples (vertically) to produce an artificial 4:2:2 signal that can then be sent over HDMI 1.4. The amount of actual color information in this case would be identical to what is contained in a 4:2:0 signal with the extra color samples there just to satisfy the HDMI specification.

    This is what happens in the case of Bluray movies which are all stored on disc using a 4:2:0 codec. But when the Bluray player outputs this video over HDMI to a TV, it converts it to 4:2:2 since that is what is supported by the HDMI spec (pre-HDMI 2.0 anyway).

    This is why there may be some confusion about the GH3's HDMI output format. The GH3's internal codec is 4:2:0 (when writing to an SD card). So somewhere along the image processing pipeline between the sensor and the SD card, the video signal gets converted to 4:2:0 subsampling. If the HDMI output happens after this conversion, it would be a 4:2:0 signal in terms of color information, output as 4:2:2 to satisfy the HDMI spec. If instead the HDMI output is from some earlier stage of the image processing pipeline (before the 4:2:0 conversion), it could be a true 4:2:2 signal that is output.

    But I haven't seen much definitive information one way or the other about this.

  • thetricksterthetrickster

    @davedv - thanks. thats very informative!

  • tommydog35tommydog35

    Thanks davedv that's a really helpful answer.

    surely it would make sense for Panasonic to output 4:2:2 through the HDMI before the conversion to 4:2:0. Otherwise what is the advantage of using the HDMI? Also do you know what the HDMI output is in terms of mbps?

    You think Panasonic would publish such specs.

  • davedvdavedv

    Video signals sent over HDMI are uncompressed, so there is no video compression codec (like H.264) that is applied in the case of HDMI output. Which means that the video bitrate is determined by the HDMI specification and depends on the video format (resolution, frame rate, color depth, and chroma subsampling). Any camera outputting an HDMI signal with the same video format (resolution, etc.) would be sending the same bitrate.

    Roughly speaking, if you had a 1920 x 1080 video signal at 30 fps, with 8-bit color depth, and 4:4:4 RGB format, you could calculate the video bitrate: 1920 x 1080 = 2073600 pixels x 8 x 3 (eight bits each for RGB) = 49766400 x 30 frames/sec = 1492992000 bits/sec Or 1492.992 Mbps

    In practice, with HDMI there is some padding in the encoding, and vertical and horizontal blanking intervals (among other things), so the total data rate being sent over the cable is slightly higher than this.

    But, in any case, certainly one advantage of using the HDMI output is that you bypass the internal H.264 encoder of the camera. And so if you take the uncompressed HDMI output signal you can then record it directly (which would take a lot of storage space), or you could record it in ProRes, DNxHD or another video codec that uses a higher bitrate (and less aggressive compression) than the built in H.264 encoder.

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