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X70: UHD in firmware v3.0 compared to HD

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    X70: UHD in firmware v3.0 compared to HD

    Hi all,

    I've just uploaded a test comparing UHD ("4K") on the X70 to HD, with firmware v3.0.

    This seems of interest particularly now that we have UHD at 100Mb/second. To my eye, HD on this camera looks pretty awesome, which I have attributed to the 10-bit pixel depth; since UHD is only 8-bit, and also has a relatively low bit-rate of 100Mb/s, I was wondering how well it holds up. Of course the resolution should be a lot better.

    So, I shot a bunch of test shots, including some low-light and shots with moving water for tons of motion. I've compiled these into movies that you can download and enjoy at your leisure. There are shots of the outside and inside of an old chapel; rocks on the cliffs below the chapel; and waves on rocks, with tons of motion in frame. It was dark in the chapel, but not dark enough to need gain -- both shots inside were wide open at f/2.8, zero gain.

    I've posted two versions; the original files can be downloaded from these pages:
    • https://vimeo.com/171821970 "UHD version" is a UHD video which contains all 6 test scenarios, with some of them having lightened versions. The HD shots have been scaled up to UHD (so of course they are less sharp).
    • https://vimeo.com/171828961 "HD version" is a 1080p video which contains the same shots, but with the UHD shots scaled down to 1080p. I've also added some "punch-ins" on selected shots; in these the HD shot has been scaled up 200% and cropped, and the UHD shot has just been croppped. This lets people with 1080p monitors see what the UHD looks like pixel-for-pixel, when seen next to the HD.


    All shots were exposed using a 95% zebra, adjusting the exposure to eliminate all zebra (except maybe in extreme hightlights). Nothing, including the exposure, was adjusted between the HD and UHD versions of shots.

    Unfortunately the clouds were patchy, so the exposure did vary a little due to that, specially in the wave shots.

    Also unfortunately, I screwed up on the picture profile; I didn't realise that UHD keeps its PP setting separately from HD. (And why the heck does it????) So all the HD shots were shot in PP6 as factory, and all the UHD shots were shot in PP "off". So ignore any colour shift. It doesn't seem to have hurt things too badly, as the exposures were basically the same. I'm going to re-test at least a little, to make sure that "PP off" doesn't do a ton of sharpening. (But based on the footage, I don't think so.)

    My observations:
    1. Framing: the UHD mode has a very slightly wider field of view -- you would think it would just be a 2:1 scaling, but apparently more is going on. The difference looks like about 6 UHD pixels horizontally.
    2. Resolution: the UHD shots are very noticeably sharper, even when watching the HD version of the movie, even without punching in. Note that there was absolutely no change to the focus, zoom or iris -- the change of framing between the HD and UHD shots is purely coming from the camera. If you're going to deliver in HD, it looks to me like you'll get much sharper results by shooting in UHD.
    3. Noise: both HD and UHD show noise when the exposure is raised, but it doesn't look a lot worse in UHD -- particularly look at the rocks in the middle of the last pair of shots; both show noise, but I don't think the UHD case is any worse.
    4. Compression: I can't see any compression artifacts in the UHD (thinking about the 100 Mb/s here), even on the wave shots where there's a ton of motion in the frame, even when the brightness has been raised a lot. (Interestingly, if I export the HD sequence at 10 Mb/s there is serious compression artifacting visible in the last shot; the UHD sequence at 40 Mb/s doesn't show it. The current exports are both 40.)


    So overall I'm pleased with the UHD. I don't see the 8-bit depth being a problem, and 100 Mb/s looks like enough. What do you think?
    Last edited by AtticusLake; 06-22-2016, 11:34 PM.


    #2
    Very nice, I am watching the 4k on a 1080p screen and it looks sharper than the 1080p footage. The lightened versions however show more noise on the 4k. I am considering the Z150 or the Panasonic DVX200, are you familiar with either one of them.

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      #3
      Thanks! As for noise, I think it's clearer in the 4k, and more smudged out in the 1080p; but I have feeling it's actually just as strong in the 1080p footage. Of course the perceived noisiness is what matters.

      I'm not familiar with those other cams, sorry.

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