Subject:
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lenses, webcams, magnafication
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Newsgroups:
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lugnet.off-topic.geek
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Date:
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Mon, 29 Oct 2001 01:41:14 GMT
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Viewed:
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213 times
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As part of my masters research I need to collect images of the leaves of
the plant that I study for later image analysis. Typically this is done
through a destructive harvest of the tissue and the image is captured
using a flatbed scanner. My situation doesn't allow for this technique
since a) the plant is threatened, and b) removing the tissue might cause
hormonal/ecophysiological changes within in the plant that will confound
later measurements (I plan on measuring three times over the next six
months).
I am looking to get the following measurements:
1. left/right distance to the edge of the leaflet from the midrib -->
symmetry index
2. leaf area
3. some measure of shape (?)
I've been working out a cool solution using a webcam(1) as the capture
device, but a problem arises when I try to look at leaf area. These
leaves vary in size from 1.5 to 8 centimeters across so the camera to
leaf distance varies to fit it the image within the frame. As many of
you must have already realized- this varies the magnafication and
therefore would produce errors in the measured area. I see three ways
to counter this problem:
1. keep a fixed focal distance *easy* (i think)
2. using some sort of lens equation figure out the magnafication for
each measurement
3. place a scale(i.e. 1cm) at leaf level and use that as a reference
image in each measurement.
1 and 3 are pretty straightfoward but if I chose to look into #2 how
would I go about doing to this for a webcam? Their lenses are tiny and
I haven't had any luck finding this spec anywhere.
-chris
1- the LEGO Vision Command Camera but my Mavica could be *easily*
swapped for it.
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