Re: Basic Setup Question

Posted by Gabriel Landini on Nov 17, 2010; 1:49pm
URL: http://imagej.273.s1.nabble.com/Basic-Setup-Question-tp3686410p3686412.html

On Wednesday 17 Nov 2010  13:21:58 you wrote:
> I am looking to set up a basic webcam (venus USB 2.0 webcam) to take a
> picture every few minutes over a period of hours, and then calculate the
> greyscale average of a particular ROI, and I would like this to be as
> automated as possible. I can find various bits and pieces - for example I
> am ok doing the ROI, but I am not sure how to tie all this together.
> Initially this would be done on a Mac, but eventually I will be running it
> on a PC too. Does anyone know of any particular plugin/script combinations
> which would be good for this?

Hi,
SambaJ had some interface to capture from a webcam, not sure if that is still
maintained or if it will drive your device.

However, I doubt that using a webcan will produce any usable data. Webcams
output lossy compressed signals and most commonly have automatic gain (in many
this is impossible to turn off). That means that the intensity measurements
will not be controlled (the image gets darker and the camera will "compensate"
for that, changing the gain). Measurements of grey intensity obtained that way
will be meaningless.

Depending on what you want to do, it might be an option to spend some time
interfacing a photocell via an AD converter (there are several cheap options
that use the parallel port or the USB), calibrate it, so you know what you get
in the signal, and use that instead.

Cheers

Gabriel