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Logitech C920 and Isadora



  • Hi,
    I'm looking forward to buying a new cam for the show I'm currently working on. My goal is to stream a hand that is drawing on a sheet of paper and display it along with a few other video streams simultaneously (picture players into projector actors). I will also use some CPU-intensive effects such as blur, so I would like to avoid as much processing on the computer as possible. A very high resolution is not that important (720p would be enough), but image quality and smoothness are (hand movements should not appear too blurry). And more importantly, I need a camera that can be manually focused/white-balanced.
    I don't know much about cameras but I stumbled across the C920 from Logitech that seems great. Someone here wrote that he could use this cam with success in Isadora, but I have a couple of questions I would like to ask you forumers/C920 users, as you are much more competent on this subject than I am.
    From what I read on various websites, the C920 (in 1080p and 720p) captures video and then encodes it to H.264, thus reducing CPU load. The "Optimizing for speed" page on Isadora website explains that H.264 can be quite heavy.
    So **question #1** is: Does this H.264 'limitation' still apply to live streams or does it just concern movie files on a drive?
    Also, it seems that 1080p (and maybe H264 encoding?) can only be obtained using proprietary Logitech Webcam Software (LWS). The C920 seems not to be compatible with common UVC, only H.264 UVC. I don't understand this well but I'm afraid I won't be able to change the brightness/focus/white balance/etc in Isadora. Note that if these settings can't be changed during the show, I can put up with it. [You might find this page helpful: [http://logitech-en-amr.custhelp.com/app/answers/detail/a_id/28951](http://logitech-en-amr.custhelp.com/app/answers/detail/a_id/28951)]
    So **question #2**: Is it possible to configure the C920 with LWS when using it with Isadora? Is Isadora compatible with this software?
    Some C920 users also reported bad frame rates, even in well lit situations.
    So **question #3**: Did you notice any drops in frame rate for 720p/1080p or is everything running at a smooth 30fps?
    And to sum up, **question #4**: Is this cam still a good choice in that respect? Or is there another model I should consider?
    Even the shortest piece of advice would be greatly appreciated, as I'm really stuck on this.
    Oh, and I'd like to use it on a PC with Windows 7.


  • Hi djinoui,
    personally I don't use the C920 to get live video streams in performances (I use camcorders with the Blackmagic Extreme to get HD quality with very little lag; and lately I have use the iphone 4S and 5S with EpocCam/Multicam software to get live video streams in HD quality in performance).
    I use the C920 for motion tracking and teaching. However, if you want  to use the C920 in performance, you can easily test the performance on your PC.
    _The Performance Monitor actor will help you to check on the framerates you get in your setup.
    _By default I get Y'CbCr 4:2:2 compression with the C920 (this is a chroma sub-sampling image encoding that uses less resolution for chroma information than luma information) - just check the Live Capture Settings/Settings/Compression and experiment with different compression types! On my MBP 2013 I get good results at 720p/30fps/high image quality (0.1-0.2 seconds lag) with the Y'CbCr 4:2:2 compression; 1080p/30fps/high image quality lags 0.3 seconds and more; frame rate drops to 20fps.
    _You can also correct the images saturation, brightness, contrast and sharpness under Live Capture Settings/Settings/Adjustments, if you need to (or use the respective actors according to your needs). Whitebalance and focus are automatic and work well in my opinion.
    _You can improve fps considerably if you set the frame rate under Live Capture Settings/Settings/Compression from best to your project's frame rate (30 fps for example).
    Hope this helps,
    best Stephan



  • Hi Stephan,

    Thanks very much for your feedback. After thinking about it for a little while, I suppose I should buy one and test it on my PC, as resolution is not my main concern. Wether Y'CbCr 4:2:2 or H.264 is finally not really important, as soon as global image quality is OK. 200ms lag is still acceptable for what we're trying to do, and so is 720p@30fps for the time being (I understand that performance depends on the computer, of course).
    The only thing I still don't get is if it's possible or not to configure white balance and focus *manually* (if it's only automatic I won't be able to use actors based on colors and contours such as ChromaKey and [FloodFill](http://forum.troikatronix.com/cgi-bin/forum/gforum.cgi?post=13235), and we're intending to make intensive use of these). Is it allowed from within the Live Capture Settings menu (inside Isadora), or is automatic the only possible mode?
    I really appreciate your help so thanks again!


  • Hi Djinoui,
    the white balance and focus is not available in the Live Capture Settings, but the image settings can be used.
    However, chroma key and your FloodFill plugin work perfectly fine (check attached print screens).
    Thanks for the plugin :-)

    Best Stephan
    601f34-djinoui1.png 999f7e-djinoui2.png



  • Hi Stephan,

    Thanks very much for your feedback. I suppose the image settings gives enough control, so it seems all good to me. Thanks for testing!
    (By the way, combining Mouse Watcher w/ Measure Color  is a brilliant idea!)


  • OK, I bought a C920 recently. Bad luck, it is properly recognized in Isadora but limited to 640x480. Installing or removing Logitech Webcam Software doesn't change this.

    My current computer doesn't meet the exact CPU requirement for this cam, but I can access the H.264 stream in GraphEdit for instance. Looks like this LWS crap limits users to some resolutions.
    But yesterday I tried [Spout](http://troikatronix.com/troikatronixforum/discussion/582/syphon-for-windows#Item_4). SpoutCam didn't register properly at first, but after reinstalling Spout, I was able to find it in Isadora as a live source stream. Spout provides a Processing example, which I tweaked for my needs (removed the TexturedCube demo stuff and used a Capture object instead). Now it works perfectly (though I must be really unlucky, because my system has nVidia Optimus, which makes Spout fall back to memoryshare mode, so it doesn't use the GPU, if I understand correctly).
    Here is the modified SpoutSender for Processing if anyone is interested. Rename the original file in SpoutInstallDir\PROCESSING\x64\SpoutSender and use this one instead.
    (Thanks again Stephan!)

    2bae6c-spoutsender.zip



  • Hello,

    Just updated to Isadora 1.5.3f25\. The C920 works perfectly now (1280x720, Logitech Webcam Software installed). No need to use SpoutCam anymore!

  • Tech Staff

    @djinoui
    regarding Spout.. check your Bios settings to see if you can turn off optimus support there.

    these instructions might help: http://forums.autodesk.com/t5/Hardware/Disabling-nVidia-Optimus-amp-Perform-Clean-Install/td-p/4363279


  • @DusX

    Thanks, but I already checked after reading your advice on the Spout forum. There's nothing I can do in my old yet up-to-date BIOS...

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