[Insight-developers] ShrinkFilter - Bugs from double precision

[Bradley Lowekamp]

To look into why my changes caused problem, I compared the computed  
index between the ImageBase::Transform and the my supposed optimized  
algebraic equivalent based on integer index operation.

http://public.kitware.com/cgi-bin/viewcvs.cgi/Code/BasicFilters/itkShrinkImageFilter.txx?root=Insight&r1=1.56&r2=1.57&sortby=date

The following is some debug information I printed comparing the two.  
Notice with the shrink factors 2 1 1, the current implementation  
repeats the second index, even though there is no shrinking being  
performs. Clearly this is a bug, and is the likely candidate for  
causing the segfault, when computed in the  
GenerateInputRequestedRegion, and the regions don't match up correctly  
with the optimized version.

The other thing to notice is the third component of the computed  
Origin. Even though the shrink factor is 1 for both cases, the origin  
changes. I can not find a reason for this. Any thoughts?

I am planning on committing the change with the matched computation in  
the ThreadedGenerateData and GernerateInputRequestedRegion methods.

ShrinkFactors: 4 2 1
  Spacing: [2, 5.4, 7.5]
Origin: [-33.35, -178.2, -179.25]


ShrinkFactors: 2 1 1
Spacing: [1, 2.7, 7.5]
Origin: [-32, -178.2, -179.75]


output         input            optimized input
Index          Index           Index
[0, 2, 0] ->  [0, 1, 0] not [0, 2, 0]
[0, 3, 0] ->  [0, 3, 0]
[0, 4, 0] ->  [0, 3, 0] not [0, 4, 0]
[0, 5, 0] ->  [0, 5, 0]
[0, 6, 0] ->  [0, 6, 0]
[0, 7, 0] ->  [0, 7, 0]
[0, 8, 0] ->  [0, 8, 0]
[0, 9, 0] ->  [0, 8, 0] not [0, 9, 0]
[0, 10, 0] -> [0, 10, 0]
[0, 11, 0] -> [0, 11, 0]
[0, 12, 0] -> [0, 12, 0]
[0, 13, 0] -> [0, 12, 0] not [0, 13, 0]
[0, 14, 0] -> [0, 14, 0]
[0, 15, 0] -> [0, 15, 0]
[0, 16, 0] -> [0, 16, 0]
[0, 17, 0] -> [0, 17, 0]
[0, 18, 0] -> [0, 17, 0] not [0, 18, 0]
[0, 19, 0] -> [0, 19, 0]
[0, 20, 0] -> [0, 20, 0]
[0, 21, 0] -> [0, 21, 0]
[0, 22, 0] -> [0, 22, 0]
[0, 23, 0] -> [0, 22, 0] not [0, 23, 0]
[0, 24, 0] -> [0, 24, 0]
[0, 25, 0] -> [0, 25, 0]
[0, 26, 0] -> [0, 26, 0]
[0, 27, 0] -> [0, 27, 0]
[0, 28, 0] -> [0, 28, 0]
[0, 29, 0] -> [0, 29, 0]
[0, 30, 0] -> [0, 30, 0]
[0, 31, 0] -> [0, 31, 0]
[0, 32, 0] -> [0, 32, 0]


On Apr 8, 2009, at 4:56 PM, Luis Ibanez wrote:

>
> Hi Brad,
>
> I would seem that your commit:
> http://www.cdash.org/CDash/viewUpdate.php?buildid=308797
>
> generated the following segmentation fault:
> http://www.cdash.org/CDash/viewTest.php?onlyfailed&buildid=308797
>
> Could you please take a look ?
>
>
>    Thanks
>
>
>       Luis
>