UVC webcam exposure under Mac OS X

Apple's Mac OS X includes drivers for USB Video Device Class (UVC) cameras, which means that most webcams, including  the Xbox Live Vision, are just plug and play without needing to install any specialist drivers. However, the Apple provided webcam software Photo Booth doesn't allow any control over things like the exposure, gain, or frames per second (FPS), which are quite important in astrophotography. And it only captured at 640 × 426 pixels. So what can we do about this?

I would like to use a particular UVC webcam, the Xbox Live Vision, USB identifiers 0x045e 0x294, but most of the problems below are down to trying to use Mac OS X for webcam astrophotography.

Although not free, iUSBcam looked possible - but surprisingly it says it is not compatible with Snow Leopard or Lion. This company seems to have switched their efforts to iGlasses 3 which does support Snow Leopard and Lion. This does allow exposure control, but I suspect it is done with image processing rather than the camera settings which is what I want. I did contact their support for clarification, but heard nothing back.

Back in July 2009, Dominic Szablewski demonstrated it was possible to control the exposure, white balance and gain directly with a demo application using QTKit. I had a little play with it - it compiled fine with Xcode 4.2 on Lion after running the update project option, but I failed to get it to show any signal from any of the USB webcams I tried - it insisted on using the laptop's built in camera.

What I would like is either a more sophisticated web camera app for the Mac that allows access to these settings and record images or movies with them, or a way of changing the settings at the driver level for all applications. That seems to be what Max Grosse set out to do in Feb 2010, write an alternative Mac UVC camera driver, which he released in March 2010. The code is in his SVN repository, so I took a look:

svn co http://svn.ioctl.eu/mac_uvc/trunk/mac_uvc

The last revision was from Nov 2010, and there doesn't seem to be any instructions which would have been on Max's website but that page was lost in an upgrade. However, I could find a uvc_mac wiki snapshot from March 2010 which included important details like the code is released under the free zLib-License, was still considered unstable, and the API likely to change. Folder uvc/ contains the uvc.framework, while UVCCap/ contains a very basic sample application (Cocoa) that uses the framework to render the video stream. There is also a third folder, UVCCap_Old which I think we can ignore. I didn't get very far with this.

Where next? Perhaps macam will assist me - I had a look on the list of web cameras supported in macam for the Xbox Live Vision camera (which I'm hooking up to my telescope). Sadly the Xbox Live Vision isn't supported in macam, just via UVC. I tried anyway, but neither it nor two other USB webcams I had seem to show up in the macam v0.9.2 application. Issue logged.

Maybe I should just spend some more money tracking down a Phillips SPC900NC which should work in macam? It would probably make life easier as this is quite a popular webcam for astrophotography, so other people have posted recommended settings etc.

Reading the CloudyNights post on Webcam Astrophotography on the Mac there are also commercial webcam drivers from IOXperts, but they seem quite old - even support for Mac OS X 10.5 Leopard is currently in beta - and they don't seem to support the Xbox webcam anyway.

On the image capture side, I've downloaded Nebulosity 2 (free demo mode), but it doesn't seem to support any USB web cameras. Likewise their free mini-app, Craterlet for Mac only handles some firewire cameras.

I've also downloaded Equinox Pro 7 (free demo mode), which do a lot of stuff but go to the menu "Connect", "Webcam" (or Apple+Shift+W) and it seems to work with my webcam - and has some sort of exposure controls. This looks promising in that I could record some movies where Jupiter was not too washed out, which seemed to be the typical result using Photo Booth. Also it only recorded QuickTime movies at 640 × 480 pixels (VGA, better than just 640 × 426 with Photo Booth), both only managing up to 10 FPS at these light levels.

However, running under Linux on my elderly old laptop, wxAstroCapture version 1.8-1 (the 23 Oct 2010 beta) offers to connect to the Xbox Live Vision at resolutions of 320×240,  352× 288,  640 × 480,  960 × 720 and 1280 × 960 pixels (YUYV). It lets me turn off auto-exposure and set the gain and shutter speed manually. It lets me adjust the gamma, brightness and try to set the frames per second (FPS) - although unsurprisingly that seems to be limited according to the image size.

It looks like life would be easier for image capture if I switched to Windows or Linux... maybe there is a role for my elderly old Linux laptop yet?

Update

I found a nice little command line app for capturing webcam frames under Mac OS X called ImageSnap, but it doesn't seem to have any code for controlling the image settings.

I've since found other public grumbles about Apple crippling their camera capture API, e.g.

There currently is no way to change the exposure, gain, etc. ... via the QTKit Capture APIs (duplicate rdar://5760371 "Ability to set brightness, gain, etc. for cameras in QTKit Capture API" if you'd like this functionality). – Brad Larson, 15 March 2011

Also see this blog post on disabling auto-exposure and auto-whitebalance features of a UVC webcam, which would also be useful for astrophotography.