[Insight-developers] DifferenceOfGaussiansGradientImageFilter
Miller, James V (Research)
millerjv@crd.ge.com
Thu, 23 Jan 2003 13:18:43 -0500
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It really just a "Difference of displaced intensities". There is nothing gaussian related to the
implementation (internal to this filter, you have to feed a smoothed image). I would even avoid the
idea of difference of displaced gaussians because I infer from that name that multiple gaussians are
used.
What is there is basically just a digital derivative where the kernel is wider than 3 elements, i.e.
instead of using a kernel
-1, 0, 1
you are using a kernel
-1, 0, ..., 0,1
where there are an odd number of 0's between the -1 and 1.
I would probably call it something like a "WideCentralDifferenceGradientImageFilter".
-----Original Message-----
From: George Stetten [mailto:george@stetten.com]
Sent: Thursday, January 23, 2003 12:50 PM
To: Miller, James V (Research)
Cc: Insight-developers (E-mail)
Subject: Re: [Insight-developers] DifferenceOfGaussiansGradientImageFilter
Jim
Our use of the phrase "Difference of Gaussian" is perhaps unfortunate. We blur the image with a
recurrent binormial filter that approximates a Gaussian, and then produce the components of the
gradient by subtracting the intensity at two points displaced along each of the cardinal directions.
This is a "Difference of Gaussian" but not in the traditional sense. The traditional DOG is two
concentric Gaussians of different scale, yielding something approximating a Laplacian, which yields
zero-crossings at the boundaries independent of orientation.
How about we change the name of our "Difference of Gaussian" to "Difference of Displaced Gaussians"
which is more specific?
George
Miller, James V (Research) wrote:
3) the calculation does not appear to be a difference of gaussian
gradient calculation
I'll defer this to George - it's based on his code. As I
understand it,
this filter approximates a DOG computation when run in tandem
with the
BinomialBlurImageFilter.
So there are lots of issues with this filter's name then. At best it computes a gradient of the
image. However, it is not doing a difference of Gaussians approach internally to the filter. If you
have to pass it a blurred image, then it is merely doing a gradient calculation. Now if I am feeding
with a BinomialBlur, then I am not really doing a difference of Gaussians either.
I would say if you can use another gradient calculator in the system, then use that. I do think it
would be nice to have a DifferenceOfGaussians filter. It should take a single intensity image and
two sigmas.
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--
George Stetten, M.D., Ph.D.
Assistant Professor, Bioengineering, U. Pitt.
Research Scientist, Robotics Institute, CMU
http://www.stetten.com <http://www.stetten.com>
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<DIV><SPAN class=3D470150918-23012003><FONT color=3D#0000ff size=3D2>It =
really just a=20
"Difference of displaced intensities". There is nothing gaussian =
related to the=20
implementation (internal to this filter, you have to feed a smoothed=20
image). I would even avoid the idea of difference of displaced =
gaussians=20
because I infer from that name that multiple gaussians are=20
used.</FONT></SPAN></DIV>
<DIV><SPAN class=3D470150918-23012003><FONT color=3D#0000ff=20
size=3D2></FONT></SPAN> </DIV>
<DIV><SPAN class=3D470150918-23012003><FONT color=3D#0000ff =
size=3D2>What is there is=20
basically just a digital derivative where the kernel is wider than 3 =
elements,=20
i.e. instead of using a kernel</FONT></SPAN></DIV>
<DIV><SPAN class=3D470150918-23012003><FONT color=3D#0000ff=20
size=3D2></FONT></SPAN> </DIV>
<DIV><SPAN class=3D470150918-23012003><FONT color=3D#0000ff =
size=3D2>-1, 0,=20
1</FONT></SPAN></DIV>
<DIV><SPAN class=3D470150918-23012003><FONT color=3D#0000ff=20
size=3D2></FONT></SPAN> </DIV>
<DIV><SPAN class=3D470150918-23012003><FONT color=3D#0000ff =
size=3D2>you are using a=20
kernel</FONT></SPAN></DIV>
<DIV><SPAN class=3D470150918-23012003><FONT color=3D#0000ff=20
size=3D2></FONT></SPAN> </DIV>
<DIV><SPAN class=3D470150918-23012003><FONT color=3D#0000ff =
size=3D2>-1, 0, ...,=20
0,1</FONT></SPAN></DIV>
<DIV><SPAN class=3D470150918-23012003><FONT color=3D#0000ff=20
size=3D2></FONT></SPAN> </DIV>
<DIV><SPAN class=3D470150918-23012003><FONT color=3D#0000ff =
size=3D2>where there are=20
an odd number of 0's between the -1 and 1.</FONT></SPAN></DIV>
<DIV><SPAN class=3D470150918-23012003><FONT color=3D#0000ff=20
size=3D2></FONT></SPAN> </DIV>
<DIV><SPAN class=3D470150918-23012003><FONT color=3D#0000ff size=3D2>I =
would probably=20
call it something like a=20
"WideCentralDifferenceGradientImageFilter".</FONT></SPAN></DIV>
<DIV><SPAN class=3D470150918-23012003><FONT color=3D#0000ff=20
size=3D2></FONT></SPAN> </DIV>
<DIV><SPAN class=3D470150918-23012003><FONT color=3D#0000ff=20
size=3D2></FONT></SPAN> </DIV>
<BLOCKQUOTE=20
style=3D"PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px =
solid">
<DIV class=3DOutlookMessageHeader dir=3Dltr align=3Dleft><FONT =
face=3DTahoma=20
size=3D2>-----Original Message-----<BR><B>From:</B> George Stetten=20
[mailto:george@stetten.com]<BR><B>Sent:</B> Thursday, January 23, =
2003 12:50=20
PM<BR><B>To:</B> Miller, James V (Research)<BR><B>Cc:</B> =
Insight-developers=20
(E-mail)<BR><B>Subject:</B> Re: [Insight-developers]=20
=
DifferenceOfGaussiansGradientImageFilter<BR><BR></FONT></DIV>Jim<BR><BR>=
Our=20
use of the phrase "Difference of Gaussian" is perhaps unfortunate. =
We=20
blur the image with a recurrent binormial filter that approximates a =
Gaussian,=20
and then produce the components of the gradient by subtracting the =
intensity=20
at two points displaced along each of the cardinal directions. =
This is a=20
"Difference of Gaussian" but not in the traditional sense. The=20
traditional DOG is two concentric Gaussians of different scale, =
yielding=20
something approximating a Laplacian, which yields zero-crossings at =
the=20
boundaries independent of orientation. <BR><BR>How about we =
change the=20
name of our "Difference of Gaussian" to "Difference of Displaced =
Gaussians"=20
which is more specific?<BR><BR>George<BR><BR>Miller, James V =
(Research)=20
wrote:<BR>
<BLOCKQUOTE =
cite=3Dmid:FBE90DFC240BA541B38A43F39913A16D04460F84@xmb02crdge=20
type=3D"cite">
<BLOCKQUOTE type=3D"cite">
<BLOCKQUOTE type=3D"cite"><PRE wrap=3D"">3) the calculation does =
not appear to be a difference of gaussian <BR>gradient =
calculation<BR></PRE></BLOCKQUOTE><PRE wrap=3D"">I'll defer this to =
George - it's based on his code. As I <BR>understand it, <BR>this =
filter approximates a DOG computation when run in tandem <BR>with the =
<BR>BinomialBlurImageFilter.<BR><BR><BR></PRE></BLOCKQUOTE><PRE =
wrap=3D""><!----><BR>So there are lots of issues with this filter's =
name then. At best it computes a gradient of the<BR>image. However, =
it is not doing a difference of Gaussians approach internally to the =
filter. If you<BR>have to pass it a blurred image, then it is merely =
doing a gradient calculation. Now if I am feeding<BR>with a =
BinomialBlur, then I am not really doing a difference of Gaussians =
either.<BR><BR><BR>I would say if you can use another gradient =
calculator in the system, then use that. I do think it<BR>would be =
nice to have a DifferenceOfGaussians filter. It should take a single =
intensity image and<BR>two =
sigmas.<BR><BR>_______________________________________________<BR>Insigh=
t-developers mailing list<BR><A class=3Dmoz-txt-link-abbreviated =
href=3D"mailto:Insight-developers@public.kitware.com">Insight-developers=
@public.kitware.com</A><BR><A class=3Dmoz-txt-link-freetext =
href=3D"http://public.kitware.com/mailman/listinfo/insight-developers">h=
ttp://publ
ic.kitware.com/mailman/listinfo/insight-developers</A><BR></PRE></BLOCKQ=
UOTE><BR><PRE class=3Dmoz-signature cols=3D"$mailwrapcol">--=20
George Stetten, M.D., Ph.D.
Assistant Professor, Bioengineering, U. Pitt.
Research Scientist, Robotics Institute, CMU
<A class=3Dmoz-txt-link-freetext =
href=3D"http://www.stetten.com">http://www.stetten.com</A>
</PRE><BR></BLOCKQUOTE></BODY></HTML>
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