[Nottingham] Webcam snapshots

[Martin]

On 23 August 2011 10:27, James Moore <jmthelostpacket at googlemail.com> wrote:
> On 18/08/2011 12:24, Martin wrote:
>>
>> Folks,
>>
>> Anyone know of how to, or any utilities, that can take a single frame
>> snapshot from a webcam *without* having the webcam running
>> continuously?
>>
>> That is: How can you use one of the new fangled HD-quality webcams as
>> a 'camera'?
>>
>> (This is also to get around the problem that you cannot use multiple
>> HD webcams on one USB2 hub...)
>>
>>
>
> um... you can... I have.
> There's a Mandriva-based ISO around called Zoneminder, which allows you to
> capture video or stills on a timebase or a motion-detect basis, from any
> number of cameras, USB or network (LAN or WAN), into a single location. If

Had a brief look at that. The problem there is a single HD-webcam
grabs the entire bandwidth available on a USB2 root hub. Hence, unless
you start adding additional USB2 interface cards so that you can have
one root hub per HD-webcam, you can't concurrently run multiple
webcams.

Unless... You could only ever have just one of them active at any instant.


I'm wanting to experiment with 3d reconstruction and want to switch
between 4 webcams. It's rather too tedious (and too slow) to manually
individually select between them in sequence with such a camorama.

Hence... Any tricks to automate selecting each webcam in sequence to
grab the 3rd frame of 3 frames of a video stream?

Or indeed use them as a snapshot camera in the first place?

(3rd frame of a 3 frames video streaming needed to allow the camera
settings to settle... First two frames usually have the wrong
exposure.)


Anyone any ideas? I think this has got to be one of those things that
has already been done...

Cheers,
Martin