Re: programming the usb cam

On Jun 7, 6:05 am, cmk...@xxxxxxxxxxx wrote:
On 6 4 , 10 00 , Lew Pitcher <lpitc...@xxxxxxxxxxxx> wrote:



On Jun 4, 2:24 am, cmk...@xxxxxxxxxxx wrote:

Hi
I have a logitech video cam, i want to programming it to capture
the screen back. Where i can download the protocol?

Sorry, Peter, but it is unclear to me what you want to do with your
webcam.
[snip]
Please clarify

Yes, i want to write a program to control the webcam directly.

OK, I need a little more clarification here. You say that you want to
"control the webcam directly"; what do you mean by "control"?

Is this "control" as in "capture images", or "control" as in "point
the camera somewhere else, and change the focus"?

If you mean "capture images", then you already have the ability with
the v4l2 (video4linux v2) set of syscalls that the Linux kernel
supports directly. If you mean "point the camera, change the focus",
then I don't think that there are any builtin facilities available.

If the V4L2 API answers your access problem, the only other question
is whether or not there is a video device driver for your brand of
webcam. You can check the Linux USB support (assuming that your webcam
is a USB connected one) for a driver - I have 4 USB webcams, all
working without problem under the Linux.

But
i don't think logitech or other web cam manufacturer will provide you
a sdk. So no API is available.

Are you certain that the v4l2 API won't do? As for "no sdk", you may
have to sign a NDA and/or pay a fee to the manufacturer to get that
sort of information. At least one Linux webcam driver was developed
that way. Otherwise, you've got a lot of debugging to do :-S

I am planning to build my linux robot
running on an arm development board.
I nearly have nothing on my embedded linux, not much library. so i
want to control the cam directly, that why i ask for a communication
protocol/API.

Well, you've got a lot of work ahead of you.

My recommendations would be to
a) use a supported webcam (IIRC, most of the logitech webcams are
supported)
b) use the V4L2 syscalls to access the video information
c) use libusb if possible to send any camera controls (rotate, tilt,
pan, zoom) directly, otherwise
d) build your own physical automation, and use the existing usb/serial/
parallel drivers to control it

Luck be with you
--
Lew

.

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