[Insight-developers] So -- no concensus on smoothing re MultiResolutionPyramidImageFilter?

Luis Ibanez luis.ibanez at kitware.com
Thu Apr 9 09:28:35 EDT 2009 


           This filter is reaching the point
           where it is not recoverable.


This discussion start looking like a symposium on how
to fix a duck-tape patch with another duck-tape patch.


I vote for :


     a) Leaving it in a state that is closer to what we
        could call backward compatible.

     b) Then mark it as deprecated,
        and discourage anybody from using it again.

     c) Write a new filter(s), with a new name(s).
        From a fresh start based on the requirements
        that we know today.


The requirements could be:

     1) Performance when no smoothing is needed.

     2) Keeping the center of mass of the images at different levels.

     3) ...more.. ?


If the requirements turn out to be conflictive, then I would vote
for writing separate variations of the filter, and make each one
of them fine tunned for its correct use.

Saturating a class with booleans and enums is a symptom that we
are failing to design a hierarchy of classes where the various
behaviors should be implemented in separate derived classes.

Using the "boolean" and "enum" approach, one would have to wonder
why is that we don't have a single monstrous itkOptimizer class,
and through dark-magic combinations of boolean settings we make it
behave like a : GradientDescent, or Powell, or Evolutionary....,
or why don't we have a single itkImageMetric class, and through
enums settings we make it behave as Mutual Information, or MeanSquares,
or NormalizedCorrelations...

There is no reason why we have to stick to a single
"MultiResolutionPyramidImageFilter" when we could have a clean
framework/hierarchy with multiple classes, where each one:


               "do one thing, do it well"



    Luis

--


PS.

     High density of "if" statements (and its cousin, the "switch")
     is an indicator of poor software design, and/or poor software
     maintenance practices. We can do much better than that...


----------------------
Stephen Aylward wrote:
> I could be misunderstanding...but shouldn't the default be "true" to
> keep backward compatibility?
> 
> Having an option to offer backward compatibility, but having the
> default be to not enable backward compatibility seems very odd (ok, it
> seems simply wrong).
> 
> Bill?
> 
> Luis?
> 
> Stephen
> 
> On Thu, Apr 9, 2009 at 7:30 AM, Hans Johnson <hans-johnson at uiowa.edu> wrote:
> 
>>Since this is considered a bug for over a year
>>http://www.vtk.org/Bug/view.php?id=7002 we should consider the fact that
>>MultiResolutionPyramidImageFilter smooths for unit shrink factors a bug that
>>would allow us to fix it (even through numerical sameness/backwards
>>compatibility will be lost).
>>
>>This is not the behavior that I would expect by reading the documentation on
>>how an Image Pyramid should be constructed (i.e. The top level should be an
>>exact copy of the reference images).
>>
>>I think that this is a bug that also affects the
>>RecursiveMultiResolutionPyramidImageFilter because it would produce
>>different results for the unit shrink factor image if I change the shrink
>>schedule from being downward divisible to being non-downward divisible.
>>This is particularly nasty because given the same "shrink schedule
>>[8,4,2,1]" the unit shrink result will be different depending on the size of
>>the input image.
>>
>>===============
>>If there are no objects today, then the solution that will be implemented
>>will be:
>>
>>1) Add a test that fails when the unit shrink image is not the same as the
>>reference image (and the m_SmoothIfUnitShrinkFactors =false).
>>2) Add the m_SmoothIfUnitShrinkFactors conditional flag to allow explicit
>>smoothing of the unit shrink factors.
>>3) Set the default to "false" in all cases.
>>===============
>>
>>
>>Regards,
>>Hans
>>
>>
>>On 4/9/09 1:56 AM, "Tom Vercauteren" <tom.vercauteren at gmail.com> wrote:
>>
>>
>>>Hi Kent,
>>>
>>>Even if there is no consensus about what the default should be, it
>>>could be add a flag that lets the user decide (as Stephen suggested).
>>>
>>>Maybe something like:
>>>  m_SmoothIfUnitShrinkFactors
>>>
>>>For backwards compatibility, the default for this flag would be:
>>>  - true for MultiResolutionPyramidImageFilter
>>>  - false for RecursiveMultiResolutionPyramidImageFilter
>>>
>>>Now, I also would like to propose a NON-backward compatible change to
>>>fix something that might be very confusing to the user.
>>>
>>>Since RecursiveMultiResolutionPyramidImageFilter wil call
>>>MultiResolutionPyramidImageFilter if the schedule is not downward
>>>divisible, I suggest that RecursiveMultiResolutionPyramidImageFilter
>>>sets
>>>
>>>internalNonRecursivePyramid->SetSmoothIfUnitShrinkFactors(this->m_SmoothIfUnit
>>>ShrinkFactors)
>>>when the schedule is not downward divisible.
>>>
>>>With this small non-backward compatible change, it would at least make
>>>things a bit clearer.
>>>
>>>Otherwise we might need a three state flag for
>>>RecursiveMultiResolutionPyramidImageFilter:
>>>  - AlwaysSmoothIfUnitShrinkFactors
>>>  - NeverSmoothIfUnitShrinkFactors
>>>  - SmoothIfUnitShrinkFactorsAndScheduleDownardDivisible (this being
>>>the default for true backwards compatibility)
>>>
>>>Thoughts anyone?
>>>
>>>Tom
>>>
>>>On Wed, Apr 8, 2009 at 23:27, kent williams <norman-k-williams at uiowa.edu>
>>>wrote:
>>>
>>>>It seems Hans assigned me yesterday to fix this 'bug':
>>>>
>>>>http://www.vtk.org/Bug/view.php?id=7002
>>>>
>>>>As is noted there, there still doesn't appear to be a consensus on how to
>>>>handle this problem.  So I've taken ownership of a bug with no clear way to
>>>>fix it.
>>>>
>>>>If the issue is truly tabled, does it need to hang around as an open bug?
>>>>
>>>>
>>>>
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> 
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> 
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