[Insight-users] Gradient filter problems

[Stephen R. Aylward]

Hi,

What you are asking for is a second-derivative-magnitude-image-filter - 
something that captures "barness" instead of "edgeness."   The issue 
becomes the scale (i.e. width) of the lines that you are looking for. 
Are all of your lines of the same width?  If so, then this filter could 
be easily created by modifying the GradientMagnitudeImageFilter...

Does that sound like what you need?

Stephen


Bjorn Hanch Sollie wrote:

> Hi all,
> 
> I find that when I use the GradientMagnitudeImageFilter I obtain
> double edges in the filtered picture.  For example single line
> (typically about one pixel wide in the data I'm working with) turns
> into two lines in the output image, one line on either side of where
> the actual line is.
> 
> The result of this is that when I do edge detection on a volume of a
> rather thin pipe-shaped structure, the filtered image contains one
> pipe within the other, and this makes it significantly harder to
> segment the picture afterwards.
> 
> I assume the filter "sees" the pixel-wide line as two transitions,
> from dark to light to dark, for example, thus producing two edges
> rather than one, but this makes little sense for my application,
> unfortunately, and I've seen other similar filters producing only one
> edge in this instance.
> 
> So, what I want is an edge-detection filter where the detected edges
> are actually in the same place as the boundaries I'm interested in.
> It isn't really obvious to me why the GradientMagnitudeImageFilter
> doesn't do this in the first place, so if I'm really looking for
> another filter, I'd be happy if someone can point me in the right
> direction.
> 
> -Bjorn
> 


-- 
===============================================
Dr. Stephen R. Aylward
Assistant Professor of Radiology
Adjunct Assistant Professor of Computer Science
http://caddlab.rad.unc.edu
aylward@unc.edu
(919) 966-9695