[Insight-users] Re: Re

[Zachary Pincus]

*Any* contour (zero-level or otherwise) with "inside" regions less and  
"outside" regions greater is a valid initial level set. You tell the  
level set filter what this contour is with SetIsoContourValue(), as I  
stated in my last email.

So, as per my last email and Luis's email, you can use such a contour  
as an initial level set. However, I have a suspicion that the numerical  
solution of the level set PDEs might be smoother (more artifact-free)  
or converge a little faster if the input is a true distance map. Others  
who know more about this issue will hopefully correct me if I am wrong.

Zach


On Jun 29, 2005, at 1:44 AM, Yixun Liu wrote:

> Thank you for your help!
>
> Can I draw this conclusion that a contour, with value zero on it and  
> inside value less or equal zero and outside value large zero, is a  
> correct initial level set? To get the initial level set,in my  
> opinion,we have no need to make the value of each pixel to equal to  
> the minimum  distance to the nearest edge.
>
>
> Yixun
>
>
> ----- Original Message -----
> From: "Zachary Pincus" <zpincus at stanford.edu>
> To: "Yixun Liu" <yxliu at fudan.edu.cn>
> Cc: "insight-users @ itk. org" <insight-users at itk.org>
> Sent: Wednesday, June 29, 2005 2:57 PM
> Subject: (ÈðÐÇÌáʾ-´ËÓʼþ¿ÉÄÜÊÇÀ¬»øÓʼþ)Re: [Insight-users] about  
> initial level set
>
>
>> Did you set the filter's IsoContourValue? This tells the filter where
>> the boundary is in the initial level set. If you don't set it, it
>> defaults to zero, which is bad for an binary image where either the
>> inside or the outside would be zero. (This is all covered in the ITK
>> software guide.)
>>
>> Also, the ITK convention is that the "inside" of a shape is defined by
>> values less that the IsoContourValue. So if your mask is zero outside
>> of the shape and 255 inside of the shape, you'd need to negate/invert
>> the image so that the inside values are less than the outside values.
>> Then, with a mask that has (say) inside with values of zero and  
>> outside
>> with values of one, you'd set the IsoContourValue to 0.5.
>>
>> Luis knows this system better than I, and will probably have some
>> additional comments/corrections about the above.
>>
>> Of course, you still might have better luck converting the binary
>> outline to a signed distance map; this might help the stability of the
>> subsequent computations. You would use either the
>> SignedDanielssonDistanceMapImageFilter (note: requires the "outside"
>> value of the binary mask to be zero), or the
>> ApproximateSignedDistanceMapImageFilter (faster, less accurate, and
>> allows arbitrary inside and outside values).
>>
>> Zach Pincus
>>
>> Department of Biochemistry and Program in Biomedical Informatics
>> Stanford University School of Medicine
>>
>>
>>
>> On Jun 28, 2005, at 11:12 PM, Yixun Liu wrote:
>>
>>> Hi,
>>>
>>> I did as you said. However, the result is wrong.
>>>
>>> I use the ShapeDetectionLevelSetImageFilter. It's first input is the
>>> segmented binary image and it's second input is a feature image,which
>>> is the output of the sigmoid filter. The result is obvious wrong.  I
>>> look for the document about this filter. It says that the first input
>>> should be a initial level set, which is different from a binary  
>>> image.
>>> So, in my opinion, some filters should be used to convert the bianry
>>> image to a distance map.
>>>
>>> Best regards,
>>>
>>> Yixun Liu
>>>
>>> ----- Original Message -----
>>> From: "Luis Ibanez" <luis.ibanez at kitware.com>
>>> To: "Yixun Liu" <yxliu at fudan.edu.cn>
>>> Cc: <insight-users at itk.org>
>>> Sent: Thursday, June 16, 2005 9:45 PM
>>> Subject: Re: [Insight-users] about initial level set
>>>
>>>
>>>>
>>>> Yixun,
>>>>
>>>>
>>>> Don't need to do anything particular.
>>>>
>>>> You can feed your binary image directly as input level set.
>>>>
>>>>
>>>> Regards,
>>>>
>>>>
>>>>    Luis
>>>>
>>>>
>>>> ----------------
>>>> Yixun Liu wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> I have a  segmented image represented by binary image. I want to  
>>>>> use
>>>>> level set to refine the segmentation based on the segmented image.
>>>>> How
>>>>> to generate a initial level set based on this binary image?
>>>>>
>>>>> Best regards,
>>>>>
>>>>> Yixun Liu
>>>>>
>>>>>
>>>>> ------------------------------------------------------------------- 
>>>>> --
>>>>> ---
>>>>>
>>>>> _______________________________________________
>>>>> Insight-users mailing list
>>>>> Insight-users at itk.org
>>>>> http://www.itk.org/mailman/listinfo/insight-users
>>>>
>>>>
>>>>
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