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Panasonic GH4 will be an incredible 1080p camera - 10 bit 4:4:4

Discussion in 'Panasonic Cameras' started by Promit, Apr 10, 2014.

  1. Promit

    Promit Mu-43 All-Pro

    Jun 6, 2011
    Baltimore, MD
    Promit Roy
    I'm going to break this post into a short version for people who understand some technical details of video, and then a longer elaboration for people who don't.

    The short version is this: The GH4 records 4K video internally at 8 bit in 4:2:0. Andrew Reid at EOSHD theorized that it should be possible to downsample this in a way that produces real 10 bit, 4:4:4 data. An alpha version of a tool to do exactly that has now been published. Sample footage is here: http://vimeo.com/91573346 It bears repeating something I said in an earlier GH4 thread: 4K capture doesn't require 4K distribution. There are major advantages to recording in 4K and downsampling to 2K for final output. It's the same reason we have 16, 24, or higher megapixel count cameras. The extra pixels improve sharpness, decrease noise, and produce a better final image. The same applies to video, maybe even more so.

    Ok, now to back up and explain some of the technicalities. There are detailed articles out there if you really want to know; I just wanted to provide a brief summary here. Human vision is much more sensitive to luminance than color. Video compression takes advantage of this by throwing away half or even three quarters of the color data and interpolating it after the fact. When half the data is thrown away, it's called 4:2:2. When three quarters is gone, it's 4:2:0. Full detail, where every pixel is a full YUV value, is 4:4:4. This has the net effect of smudging color detail, particularly on sharp edges. It ruins color keying and can be a real hassle for color grading. From the EOSHD post:
    gh4-colour-sampling-660x466.
    Most of you are probably familiar with 8 bit versus 10 bit; it improves the number of color gradations that can be properly represented by quite a bit. It's very easy to get banding artifacts in 8 bit, where things that should show subtle color changes don't. This is an exaggerated example:
    Colour_banding_example01.
    These kinds of details are a big reason that modern movies can still be recorded in 1080p or 2.5k and shown on large screens without breaking apart. The raw resolution doesn't sound higher than consumer equipment, but they're recording a lot more data in both color and luminance detail. While a number of consumer cameras can do this, they come with big hassles. External recorders may be required, or they may be recording fully RAW which looks great but consumes enormous amounts of card and disk space.
     
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  2. PhilS

    PhilS Mu-43 Veteran

    261
    Oct 24, 2012
    Brisbane, Australia
    Phil Savory
    This camera sure has piqued my interest
     
  3. TheRenaissanceMan

    TheRenaissanceMan Mu-43 Regular

    84
    Oct 11, 2013
    The whole downsampling 4K 8 bit 4:2:0 into 1080p 10 bit 4:4:4 idea has been largely torn apart over on the EOSHD forums. Not only does the math work out more like 8.67 bits--not much improvement--but it grades exactly the same as the original 8 bit files. Using an external recorder to get 10 bit Prores 4:2:2 should be a much bigger step up, be it 1080p or 4K.

    http://www.eoshd.com/comments/topic...c-gh4-4k-prores-next-to-arri-alexa-2k-prores/

    Sent from my SCH-I535 using Mu-43 mobile app
     
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  4. tosvus

    tosvus Mu-43 Top Veteran

    632
    Jan 4, 2014
    I'd like to see some more real life results before passing judgement. I have seen a couple of examples that seemed more promising as well. It is true that if the algorithms that do the compression in camera are not optimized at all, mathematically you can expect about 8.67 bits accuracy on average. However, we don't know exactly how Panasonic implemented the in camera processing. In a best case scenario (which granted is unlikely), they could actually make sure that data is stored in such a way that you will get 10 bit accuracy out when down-converting. (This is possibly because a 4K picture has 4 times more pixels to store information, and 8 bit to 10 bit also happens to take 4 times more space, so space wise, IF DONE PROPERLY, you can store enough info in 4k 8-bit to get true 1080p 10-bit.). It is probably too much to hope that Panasonic added the fairly few lines of code that would be needed (but that would increase CPU usage to some extent), but not impossible I suppose, and maybe it could be fixed in a firmware update in the future (depending on where the logic resides).
     
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  5. TheRenaissanceMan

    TheRenaissanceMan Mu-43 Regular

    84
    Oct 11, 2013
    I was referring more to recording internal 4K and converting in post. Panasonic's internal 1080p processing still yields 8 bit 4:2:0 files. It may be possible to do a better job of downscaling 4K to 1080p, but the fact is that most of the tonal range was already thrown away once the 8bit encoding took place. Clipped highlights and crushed blacks will stay clipped highlights and crushed blacks, no matter what you do to them in post. It's a cool idea and a no-brainer for those capturing in 4K for 1080p delivery, but I still haven't seen anything to indicate the kind of jump in quality that uncompressed HDMI would give.

    Sent from my SCH-I535 using Mu-43 mobile app
     
  6. Lobbamobba

    Lobbamobba Mu-43 Veteran

    388
    May 15, 2013
    Sweden
    For me its not about grading. I have test graded the 4K, 4K downsampled and 4K downsampled by my self and its all gradable enough.
    What I think I have found is that the 4K and 2K 4:4:4 is much more durable for ading sharpening without aliasing artefacts. I have to test more before I can really confirm that (have a preorder).

    BUT what the 4:4:4 thing does do is getting the camera over thre threshold for HD broadcast where the limit often is 50mbit/s in a 4:2:2 colorspace. Granted most chanels will sometimes make acceptions depending on how good your video is but its one less thing for them to concider.
    But as always, they care more about good audio than good picture so get that mic close :)
     
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  7. RRRoger

    RRRoger Mu-43 Regular

    57
    Apr 28, 2014
    Monterey Bay
    How about just recording thru HDMI to something like the Odyssey 7 or Q or Atomos Shogun 4k?
     
  8. Promit

    Promit Mu-43 All-Pro

    Jun 6, 2011
    Baltimore, MD
    Promit Roy
    Sure - if you want to spend a camera's worth of money again on the recorder, plus rig it up (with power?).
     
  9. RRRoger

    RRRoger Mu-43 Regular

    57
    Apr 28, 2014
    Monterey Bay
    I am already investing more than a camera's worth in lens.

    Both of these have plates for cheap Sony and other batteries.
    Both have 7" high definition monitors with effects for focus aid.
    Both can record at a much higher bit rate than the in-camera card.
     
  10. Promit

    Promit Mu-43 All-Pro

    Jun 6, 2011
    Baltimore, MD
    Promit Roy
    Then go for it. It's clearly something the GH is built to handle, and handle well. I did not mean to imply that it's a bad idea, but I think that relatively few people will be using the camera fully rigged. It's a rather different scenario for usage than what is common in this particular niche, is all. Personally I use a compact portable rig to handle some custom audio stuff and a follow focus. While a recorder/monitor wouldn't be totally unreasonable, I'm happy with the camera's ability to deliver high quality internal recordings. I don't feel the extra cost or weight benefits me. If you're setting up for broadcast or on-set style usage, by all means do what works for you.