[vtkusers] A Simple Question on vtkContourFilter

[Bill Lorensen]

The selection of the isosurface value very much depends on the data. The
contour filter does not threshold the data. It creates a surface at the
value specified and does sub voxel interpolation. Perhaps you should read
up on isosurface extraction. Here is the original Marching Cubes paper:
http://www.marchingcubes.org/images/f/f9/MarchingCubes.pdf

Here is a wikipedia page:
http://en.wikipedia.org/wiki/Isosurface



On Sun, Jul 7, 2013 at 12:25 PM, Hayden Smith <s_hayden_28 at yahoo.com> wrote:

> Hi,
>     I am not quite clear about binary volume. The original images were
> gray scale images. But I think definitely some binarization took place when
> "skinExtractor 0 127.5" is called. If I use "skinExtractor 0 30", the
> output is quite different. I just want to know how the threshold has been
> selected. Also I would like to know whether vtkImageCast or vtkImageReader
> do any filtering of images as I also used these to read and process the
> images.
>    It would be great if I get some clarification.
>
> Thanks,
> Hayden.
>
>
>    *From:* Bill Lorensen <bill.lorensen at gmail.com>
> *To:* Hayden Smith <s_hayden_28 at yahoo.com>
> *Cc:* VTK Users <vtkusers at vtk.org>
> *Sent:* Sunday, July 7, 2013 7:04 AM
>
> *Subject:* Re: [vtkusers] A Simple Question on vtkContourFilter
>
>
> It is not a binary volume, correct?
>
> I would expect that the 127 and 255 isosurfaces would be different.
>
>
> On Sat, Jul 6, 2013 at 10:03 PM, Hayden Smith <s_hayden_28 at yahoo.com>wrote:
>
> Hi,
>    It is 0 to  255.
>
> Thanks,
> Hayden.
>
>    *From:* Bill Lorensen <bill.lorensen at gmail.com>
> *To:* Hayden Smith <s_hayden_28 at yahoo.com>
> *Cc:* "vtkusers at vtk.org" <vtkusers at vtk.org>
> *Sent:* Saturday, July 6, 2013 7:05 AM
>
> *Subject:* Re: [vtkusers] A Simple Question on vtkContourFilter
>
> What is the range of your scalar data?
>
>
>
> On Fri, Jul 5, 2013 at 6:44 PM, Hayden Smith <s_hayden_28 at yahoo.com>wrote:
>
> Hello,
>       I have attached two images: the first one using "skinExtractor
> SetValue 0 127.5" and the second one "skinExtractor SetValue 0  255". Both
> showing the very similar output. My question as binarization on image is
> performed, how the threshold has been calculated as both values showing the
> similar output.
>
> Thanks,
>
> Hayden.
>
>
>    *From:* Bill Lorensen <bill.lorensen at gmail.com>
> *To:* Hayden Smith <s_hayden_28 at yahoo.com>
> *Cc:* "vtkusers at vtk.org" <vtkusers at vtk.org>
> *Sent:* Thursday, July 4, 2013 6:04 AM
>
> *Subject:* Re: [vtkusers] A Simple Question on vtkContourFilter
>
> If your data is 8 bit data, then the effect is similar to thresholding.
> Set the value to 127.5 and you will see an isosurface that has more
> character.
>
>
> On Wed, Jul 3, 2013 at 4:14 PM, Hayden Smith <s_hayden_28 at yahoo.com>wrote:
>
> Hello,
>      Thanks for the reply. But I need a little  bit clarification. When I
> use 'skinExtractor SetValue 0 255', it generates one iso-surface. Does it
> threshold the image into a binary image?
>
> Thanks again.
>
> Hayden.
>
>
>
>     *From:* Bill Lorensen <bill.lorensen at gmail.com>
> *To:* Hayden Smith <s_hayden_28 at yahoo.com>
> *Cc:* "vtkusers at vtk.org" <vtkusers at vtk.org>
> *Sent:* Tuesday, July 2, 2013 3:45 PM
> *Subject:* Re: [vtkusers] A Simple Question on vtkContourFilter
>
> skinExtractor GenerateValues 4 0 255 will extract 4 isosurfaces
>      Value 0: 0
>       Value 1: 85
>       Value 2: 170
>       Value 3: 255
>
> where
> skinExtractor SetValue 0 255
> will extract 1 isosurface with value
> 255
>
>
>
>
> On Tue, Jul 2, 2013 at 4:17 PM, Hayden Smith <s_hayden_28 at yahoo.com>wrote:
>
> Hello,
>          I have a simple question on vtkContourFilter. What is the
> difference between  the following two pieces of code:
>
>         vtkContourFilter skinExtractor
>                                     skinExtractor SetInput [v16 GetOutput]
>                                     eval skinExtractor GenerateValues 4 0
> 255
>                                     skinExtractor Update
>
>
>        vtkContourFilter skinExtractor
>                                    skinExtractor SetInput [v16 GetOutput]
>                                    skinExtractor SetValue 0 255
>                                    skinExtractor Update
>
>
> If I use 'eval skinExtractor GenerateValues 4 0 255' in vtkContourFilter,
> the reconstructed output is noisy whereas if I use 'skinExtractor SetValue
> 0 255', the output is better and much clear. Could any one clarify me how
> these two commands are making the difference in output?
> Thanks in advance.
>
>
> Hayden
>
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