The resulting units are in world coordinates. You will not need to divide by spacing. The sigma is also in world coordinates.<br><br>Kishore<br><br><div class="gmail_quote">On Tue, Sep 8, 2009 at 11:49 AM, Gomez Herrero, Alberto <span dir="ltr"><<a href="mailto:alberto.gomez-herrero@philips.com">alberto.gomez-herrero@philips.com</a>></span> wrote:<br>
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<p><span style="font-size: 11pt; color: rgb(31, 73, 125);" lang="EN-US">Hello all,</span></p>
<p><span style="font-size: 11pt; color: rgb(31, 73, 125);" lang="EN-US"> </span></p>
<p><span style="font-size: 11pt; color: rgb(31, 73, 125);" lang="EN-US">this is a question regarding derivative filters in general and the RecursiveGaussianImageFilter in particular.</span></p>
<p><span style="font-size: 11pt; color: rgb(31, 73, 125);" lang="EN-US"> </span></p>
<p><span style="font-size: 11pt; color: rgb(31, 73, 125);" lang="EN-US">When we compute, say, the first order derivative of, say, a 2D image “ I“ we get two images of the same size, “Ix”, and “Iy”. My question is,
the resulting value (i.e. the Ix and Iy gray levels) is expressed in what units?, I mean, if the gradient is defined as increment_of_gray_level / increment_of_distance_in_world_coordinates, everything is ok; but if this filter works as a simple pixelwise convolution
mask, then the gradient is in increment_of_gray_level / increment_of_pixels. In that case, I need to divide by the spacing to get the right units.</span></p>
<p><span style="font-size: 11pt; color: rgb(31, 73, 125);" lang="EN-US"> </span></p>
<p><span style="font-size: 11pt; color: rgb(31, 73, 125);" lang="EN-US">I guess this is a very basic question, but I really need to make sure that this filters work as the first definition. I can’t find it in the
code, I only know that the sigma for the smoothing is in world coordinates though…</span></p>
<p><span style="font-size: 11pt; color: rgb(31, 73, 125);" lang="EN-US"> </span></p>
<p><span style="font-size: 11pt; color: rgb(31, 73, 125);" lang="EN-US">Anyone can clarify this please?</span></p>
<p><span style="font-size: 11pt; color: rgb(31, 73, 125);" lang="EN-US"> </span></p>
<p><span style="font-size: 11pt; color: rgb(31, 73, 125);" lang="EN-US">Thanks,</span></p>
<p><span style="font-size: 11pt; color: rgb(31, 73, 125);" lang="EN-US"> </span></p>
<p><span style="font-size: 11pt; color: rgb(31, 73, 125);" lang="EN-US">Alberto</span></p>
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