Hello,
Hello,
Guy Keren said:
in the dark, movement causes only a few pixels to change
1) A lot depends of course on the type of the WebCam. I had tested Logitech
4000 Pro and it gave
very good results in darkness; At first I did not belive the quality of what
I saw. (If I am not wrong it is relatively more expensive than the average).
2) Specifically regarding what Amichai Rotman asked this point is probably
less important (since kindergardens work at
daylight) ; But he mentioned that he wants to use a couple of USB WebCams
, and also
that he want to use it on old PIII machine. If he insists on more than one
WebCam , this can pose
a problem in terms of Bandwidth/Power.
It also depends on how many free USB ports he has
(and sometimes connecting a USB hub won't solve the problem because of
power/bw considerations;
though sometimes it does work, as you probably know). Also the type of USB
Host Controller can have some significance in
some cameras (the most common USB Host Controllers on Intel x386 based PCs
are OHCI and UHCI).
You can get details on USB devices connected to your Linux (like MxPwr and
MxPS , which are max power and max packet size ) by cat
/proc/bus/usb/devices.
You can also get it visually if you install USBView from
http://www.kroah.com/linux-usb
This is a gtk based application which GregKH wrote for viewing USB devices.
USB webcams usually use high speed isochronous (ISO) transfers.
However , it seems to me that the best thing to do, instead of delving into
the complexities of
linux USB layer and starting meaurmenets (and it is quite complex) is
simply connect more than one webcam
and run some tests.
There is another aspect here - the audio; some webcams have a built in USB
microphone. (Like logitech 4000 , logitech quickcam messenger, some Creative
Labs models,
and many more). It is important to disable the USB audio (assuming that it
is not needed) in these
tests; it takes quite a bandwidth. (You can achieve it simply by removing
the USB audio driver running "rmmod audio.")
If have some experience in video4linux and Linux USB and if anyone
interested in more details on Linux USB , he is invited to read an article I
wrote titled : "An Overview of Linux USB" which was published in
LinuxJournal last month : http://www.linuxjournal.com/article/8093
(Though this article deals generally with USB layer , it has some
relevance to using Video4Linux 1 devices).
good luck,
Regards,
Rami Rosen
From: guy keren <[EMAIL PROTECTED]>
To: Yoni Levy <[EMAIL PROTECTED]>
CC: Amichai Rotman <[EMAIL PROTECTED]>, "" <[email protected]>
Subject: motion (was: Re: WebCam Server)
Date: Sun, 29 May 2005 03:40:46 +0300 (IDT)
On Sat, 28 May 2005, Yoni Levy wrote:
> Hello, there is an application called motion which might help you, it
> records a video or captures a picture when it detects motion .
> You can place a camera near the entrance with motion running, and it
> will take a picture of anyone entering ...
and it indeed work(ed) when i tried it (about 2 years ago), to spy on what
my dog was doing when i wasn't home. i found one problem: the way that
'motion' is defined, is by the number of pixels of difference between two
consecutive images. this made it hard to use with light canges (in the
dak, movement causes only a few pixels to change, so it requires a low
threshold. in the light, movement causes much more pixels to change. it
was also not possible to define where in the pictures to make these
calculations - it takes the entire picture for this calculation, whether
you like it or not.
thus, you need to do some "calibrating" for your lighting and movement
conditions, and then it works quite well. it also only records once
picture every X seconds, so it does not fill your hard drive too quickly.
good luck,
--
guy
"For world domination - press 1,
or dial 0, and please hold, for the creator." -- nob o. dy
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To unsubscribe, send mail to [EMAIL PROTECTED] with
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Regards,
Rami Rosen
MxPwr
From: guy keren <[EMAIL PROTECTED]>
To: Yoni Levy <[EMAIL PROTECTED]>
CC: Amichai Rotman <[EMAIL PROTECTED]>, "" <[email protected]>
Subject: motion (was: Re: WebCam Server)
Date: Sun, 29 May 2005 03:40:46 +0300 (IDT)
On Sat, 28 May 2005, Yoni Levy wrote:
> Hello, there is an application called motion which might help you, it
> records a video or captures a picture when it detects motion .
> You can place a camera near the entrance with motion running, and it
> will take a picture of anyone entering ...
and it indeed work(ed) when i tried it (about 2 years ago), to spy on what
my dog was doing when i wasn't home. i found one problem: the way that
'motion' is defined, is by the number of pixels of difference between two
consecutive images. this made it hard to use with light canges (in the
dak, movement causes only a few pixels to change, so it requires a low
threshold. in the light, movement causes much more pixels to change. it
was also not possible to define where in the pictures to make these
calculations - it takes the entire picture for this calculation, whether
you like it or not.
thus, you need to do some "calibrating" for your lighting and movement
conditions, and then it works quite well. it also only records once
picture every X seconds, so it does not fill your hard drive too quickly.
good luck,
--
guy
"For world domination - press 1,
or dial 0, and please hold, for the creator." -- nob o. dy
=================================================================
To unsubscribe, send mail to [EMAIL PROTECTED] with
the word "unsubscribe" in the message body, e.g., run the command
echo unsubscribe | mail [EMAIL PROTECTED]
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