Posted by
H. Gluender on
URL: http://imagej.273.s1.nabble.com/polygon-selection-tp3700848p3700855.html
Dear Kenneth Sloan,
nice to hear some current news about the apparently advanced
religious debate in your country...
>>Since the pixels are point samples, not areas,
>
>This is a common point of view, but in my opinion it is not the most
>useful one.
>
>There are at least 3 different working assumptions you can make
>about how to treat pixels and co-ordinates - and I fear that there
>is not universal agreement among all IJ users/developers.
>
>The dangerous part is that each camp often assumes that their view
>is "obviously" the correct one. That way be religious wars.
>
>--
>Kenneth Sloan
>
[hidden email]
>Computer and Information Sciences +1-205-934-2213
>University of Alabama at Birmingham FAX +1-205-934-5473
>Birmingham, AL 35294-1170
http://www.cis.uab.edu/sloan/Because on this list we are dealing with scientific image processing,
we should try to solve certain issues mathematically, i.e. in a
hopefully objective fashion.
Images in digital computers are represented as arrays of numbers and
numbers aren't spatially extended.
Pixels (Picture Elements) -- sometimes (and in the following)
understood as more or less tiny and mostly square areas -- mainly are
a means for visualization and printing, they represent the most
simple interpolation between samples, i.e. the above mentioned
numbers. As we all know, this interpolation is cheap but inadequate.
Regarded as interpolated samples, such extended pixels of course have
a defined area and side-length(s) that may be even calibrated.
To answer the original question, of where to localize the sample
value (with respect to the pixel area), depends on how the
interpolation function -- i.e. the square or rectangular area -- is
defined. The origin of this interpolation function may be at the
center, or at one of its corners, or wherever you like.
If one knows the exact way digital images have been acquired, this
knowledge could be used to choose the origin of the interpolation
function more adequately, but this is a topic that should be treated
in a different thread...
Best
--
Herbie
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http://www.gluender.de>