Seeking In-Band Logitech C920 USB Webcam Manual Focus Control Strategy: Out of band workaround described.

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mysterylectricity
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Joined: Sat Jan 07, 2017 2:09 am

Seeking In-Band Logitech C920 USB Webcam Manual Focus Control Strategy: Out of band workaround described.

Post by mysterylectricity » Sun Aug 20, 2017 3:49 am

Hello world,

I'm trying to figure out how to manually control focus, sharpness, etc. of my Logitech C920 USB webcam, preferably from within ZoneMinder and preferably on a time-varying basis.

I see 3 potential strategies:

1)I've been fiddling with uvcdynctrl and find it promising, it allows access to the needed controls without interference with/from ZM. In theory I could run uvcdynctrl from RC files and crontab entries and achieve my goals. But I would appreciate some advice as to where to put my initial RC-file type scripting. My fear is that if I roll my own with no advice, I'll come up with something that seems stable but may fail if the system boots out-of-sequence. Haven't tested to see if ZM loads the camera with ZM defaults (might fiddle with it tonight).

2)Go the orthodox route and come up with Python control scripts: but I don't know Python and seems overblown for my purposes.

3)On each of the Monitor Feeds, I find a Settings link. This link brings up a table populated with Brightness, Contrast, Hue, and Colour controls (note Hue is not supported by the C920, the fact of which leads to periodic warnings in ZM top level log.) And sure enough, modifications in this table are accurately reflected when polling the cameras with uvcdynctrl. But I can't find any information as to how this table is built or how to modify it. Any tips for me?

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iconnor
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Re: Seeking In-Band Logitech C920 USB Webcam Manual Focus Control Strategy: Out of band workaround described.

Post by iconnor » Tue Aug 22, 2017 2:04 pm

So... in the local v4l code we have functions that get/set these values. The code is in C++ and is accessed using the zmu program.

mysterylectricity
Posts: 18
Joined: Sat Jan 07, 2017 2:09 am

Re: Seeking In-Band Logitech C920 USB Webcam Manual Focus Control Strategy: Out of band workaround described.

Post by mysterylectricity » Fri Jan 19, 2018 1:28 am

Hmmm, well I don't program in C++ either, but if I examine that piece of code I might be able to add entries to the table or at least replace the default table entries with entries I find more useful. If I were to try this and compile ZM myself:

What file would I modify, and:

Would I need to then recompile all of ZM, if not what might be the command line to compile the module and where would I put the resulting binary?

Thank you!

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