The RecursiveGaussian filter doesn't use convolution.<br><br>The value of sigma is set in physical coordinates.<br><br>The output pixel values will have units of :<br><br> input intensity values / physical coordinates<br>
<br> *IF* you use the FirstOrder setting.<br><br>Note that there are also ZeroOrder and SecondOrder<br>settings.<br><br>In which case the intensity units of the output will be:<br><br>ZeroOrder: input intensity units<br>
<br>Second Order : input intensity units / (physical units)^2<br><br><br><br> Regards,<br><br><br> Luis<br><br><br><br>-------------------------------------------------------------------------------<br><div class="gmail_quote">
On Wed, Sep 9, 2009 at 9:51 AM, Oleksandr Dzyubak <span dir="ltr"><<a href="mailto:adzyubak@gmail.com">adzyubak@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Don't you change the units while convolving with the Gaussian?<br>
<br>
Alex<br>
<br>
Kishore Mosaliganti wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div class="im">
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><div><div></div><div class="h5">
On Tue, Sep 8, 2009 at 11:49 AM, Gomez Herrero, Alberto <<a href="mailto:alberto.gomez-herrero@philips.com" target="_blank">alberto.gomez-herrero@philips.com</a> <mailto:<a href="mailto:alberto.gomez-herrero@philips.com" target="_blank">alberto.gomez-herrero@philips.com</a>>> wrote:<br>
<br>
Hello all,<br>
<br>
<br>
this is a question regarding derivative filters in general and the<br>
RecursiveGaussianImageFilter in particular.<br>
<br>
<br>
When we compute, say, the first order derivative of, say, a 2D<br>
image “ I“ we get two images of the same size, “Ix”, and “Iy”. My<br>
question is, the resulting value (i.e. the Ix and Iy gray levels)<br>
is expressed in what units?, I mean, if the gradient is defined as<br>
increment_of_gray_level /<br>
increment_of_distance_in_world_coordinates, everything is ok; but<br>
if this filter works as a simple pixelwise convolution mask, then<br>
the gradient is in increment_of_gray_level / increment_of_pixels.<br>
In that case, I need to divide by the spacing to get the right units.<br>
<br>
<br>
I guess this is a very basic question, but I really need to make<br>
sure that this filters work as the first definition. I can’t find<br>
it in the code, I only know that the sigma for the smoothing is in<br>
world coordinates though…<br>
<br>
<br>
Anyone can clarify this please?<br>
<br>
<br>
Thanks,<br>
<br>
<br>
Alberto<br>
<br>
<br>
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