No subject
Mon Aug 10 18:29:21 EDT 2009
<br>
RecursiveGaussianImageFilter <<a href=3D"http://www.itk.org/Doxygen/html=
/classitk_1_1RecursiveGaussianImageFilter.html" target=3D"_blank">http://ww=
w.itk.org/Doxygen/html/classitk_1_1RecursiveGaussianImageFilter.html</a>>=
; is the base class for recursive filters that approximate convolution with=
the Gaussian kernel.<br>
<br>
In this case, wouldn't the units from the RecursiveGaussian filter matc=
h those you would have<br>
from the convolution?<br>
<br>
Alex<br>
<br>
Luis Ibanez wrote:<br>
<blockquote class=3D"gmail_quote" style=3D"border-left: 1px solid rgb(204, =
204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div class=3D"im"=
>
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>
=A0 =A0 =A0 input intensity values / =A0physical coordinates<br>
<br>
=A0 =A0*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: =A0 =A0 =A0input intensity units<br>
<br>
Second Order : =A0input intensity units / (physical units)^2<br>
<br>
<br>
<br>
=A0 =A0Regards,<br>
<br>
<br>
=A0 =A0 =A0 =A0 Luis<br>
<br>
<br>
<br>
---------------------------------------------------------------------------=
----<br></div><div><div></div><div class=3D"h5">
On Wed, Sep 9, 2009 at 9:51 AM, Oleksandr Dzyubak <<a href=3D"mailto:adz=
yubak at gmail.com" target=3D"_blank">adzyubak at gmail.com</a> <mailto:<a hre=
f=3D"mailto:adzyubak at gmail.com" target=3D"_blank">adzyubak at gmail.com</a>>=
;> wrote:<br>
<br>
=A0 =A0Don't you change the units while convolving with the Gaussian?<=
br>
<br>
=A0 =A0Alex<br>
<br>
=A0 =A0Kishore Mosaliganti wrote:<br>
<br>
=A0 =A0 =A0 =A0The resulting units are in world coordinates. You will not<=
br>
=A0 =A0 =A0 =A0need to divide by spacing. The sigma is also in world coord=
inates.<br>
<br>
=A0 =A0 =A0 =A0Kishore<br>
<br>
=A0 =A0 =A0 =A0On Tue, Sep 8, 2009 at 11:49 AM, Gomez Herrero, Alberto<br>
=A0 =A0 =A0 =A0<<a href=3D"mailto:alberto.gomez-herrero at philips.com" ta=
rget=3D"_blank">alberto.gomez-herrero at philips.com</a><br>
=A0 =A0 =A0 =A0<mailto:<a href=3D"mailto:alberto.gomez-herrero at philips.=
com" target=3D"_blank">alberto.gomez-herrero at philips.com</a>><br>
=A0 =A0 =A0 =A0<mailto:<a href=3D"mailto:alberto.gomez-herrero at philips.=
com" target=3D"_blank">alberto.gomez-herrero at philips.com</a><br>
=A0 =A0 =A0 =A0<mailto:<a href=3D"mailto:alberto.gomez-herrero at philips.=
com" target=3D"_blank">alberto.gomez-herrero at philips.com</a>>>> wr=
ote:<br>
<br>
=A0 =A0 =A0 =A0 =A0 Hello all,<br>
<br>
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 this is a question regarding deri=
vative filters in general<br>
=A0 =A0 =A0 =A0and the<br>
=A0 =A0 =A0 =A0 =A0 RecursiveGaussianImageFilter =A0in particular.<br>
<br>
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 When we compute, say, the first o=
rder derivative of, say, a 2D<br>
=A0 =A0 =A0 =A0 =A0 =A0image =93 I=93 we get two images of the same size, =
=93Ix=94, and<br>
=A0 =A0 =A0 =A0=93Iy=94. My<br>
=A0 =A0 =A0 =A0 =A0 question is, =A0the resulting value (i.e. the Ix and I=
y gray<br>
=A0 =A0 =A0 =A0levels)<br>
=A0 =A0 =A0 =A0 =A0 is expressed in what units?, I mean, if the gradient i=
s<br>
=A0 =A0 =A0 =A0defined as<br>
=A0 =A0 =A0 =A0 =A0 increment_of_gray_level /<br>
=A0 =A0 =A0 =A0 =A0 increment_of_distance_in_world_coordinates, everything=
is<br>
=A0 =A0 =A0 =A0ok; but<br>
=A0 =A0 =A0 =A0 =A0 if this filter works as a simple pixelwise convolution=
<br>
=A0 =A0 =A0 =A0mask, then<br>
=A0 =A0 =A0 =A0 =A0 the gradient is in increment_of_gray_level /<br>
=A0 =A0 =A0 =A0increment_of_pixels.<br>
=A0 =A0 =A0 =A0 =A0 In that case, I need to divide by the spacing to get t=
he<br>
=A0 =A0 =A0 =A0right units.<br>
<br>
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 I guess this is a very basic ques=
tion, but I really need to<br>
=A0 =A0 =A0 =A0make<br>
=A0 =A0 =A0 =A0 =A0 sure that this filters work as the first definition. I=
<br>
=A0 =A0 =A0 =A0can=92t find<br>
=A0 =A0 =A0 =A0 =A0 it in the code, I only know that the sigma for the<br>
=A0 =A0 =A0 =A0smoothing is in<br>
=A0 =A0 =A0 =A0 =A0 world coordinates though=85<br>
<br>
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Anyone can clarify this please?<b=
r>
<br>
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Thanks,<br>
<br>
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Alberto<br>
<br>
<br>
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 -----------------------------------------=
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</blockquote></div><br>
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