[ITK Community] Bug in DefaultVectorPixelAccessor

[Bradley Lowekamp]

OK,

Then another approach is to take advantage that the iterators are default constructible. Something like this:

ImageRegionIterator it2;
if (myfeatureImage2)
{
	it = ImageRegionIterator(myfeatureImage2, region);
}

There are a lot of options.

Hope one works for you,
Brad

On Mar 11, 2014, at 9:04 AM, Jan Ehrhardt <ehrhardt at imi.uni-luebeck.de> wrote:

> Hi Brad,
> 
> yes this is an alternative way, but the code inside the loop has approx. 200 lines (is quite complicated stuff) and I'm still testing and in your solution, I have to maintain the code four times...
> 
> Best regards,
> Jan
> 
> On 03/11/2014 01:55 PM, Bradley Lowekamp wrote:
>> Hello,
>> 
>> You are right that the GetPixel methods are slow, but that's why iterators are recommended.
>> 
>> Currently you are trying to have you "if( featureImage2 )" in side the per-pixel loop. Not only does this cause you iterator initialization issue it also is slower of have this if statement inside the loop.
>> 
>> Here is an alternative way to construct your logic:
>> 
>> https://github.com/InsightSoftwareConsortium/ITK/blob/master/Modules/Filtering/ImageFilterBase/include/itkBinaryFunctorImageFilter.hxx#L224-L297
>> 
>> Hope this help,
>> Brad
>> 
>> On Mar 11, 2014, at 8:34 AM, Jan Ehrhardt <ehrhardt at imi.uni-luebeck.de> wrote:
>> 
>>> Hi Matt,
>>> 
>>> yes, I currently use the ITK iterators, but I have the following problem. 
>>> 
>>> Standard code looks like:
>>> 
>>> itk::ImageRegionIterator<ImageType1> it( radius, myImage, region );
>>> itk::ImageRegionIterator<ImageType2> featureIt1( radius, featureImage1, region );
>>> itk::ImageRegionIterator<ImageType3> featureIt2( radius, featureImage2, region );
>>> 
>>> it.GotoBegin();
>>> featureIt1.GotoBegin();
>>> featureIt2.GotoBegin();
>>> 
>>> while(!it.IsAtEnd())
>>> {
>>>    // do some complicated processing stuff with or without feature1 and/or feature2
>>> 
>>>   ++it;
>>>   ++featureIt1;
>>>   ++featureIt2;
>>> }
>>> 
>>> I only know at runtime, whether featureImage1 and/or featureImage2 are available. If
>>> featureImage1 or featureImage2 is NULL, a segmentation fault occurs.
>>> 
>>> Therefore, I have currently implemented:
>>> 
>>> itk::ConstNeighborhoodIterator<ImageType1> it( radius, myImage, region );
>>> 
>>> it.GotoBegin();
>>> 
>>> while(!it.IsAtEnd())
>>> {
>>>    currentIndex=it.GetIndex();
>>>    if( featureImage1.IsNotNull())
>>>    {
>>>         // use featureImage1->GetPixel(currentIndex) to process feature 1
>>>     }
>>>     if( featureImage2.IsNotNull())
>>>    {
>>>         // use featureImage2->GetPixel(currentIndex) to process feature 2
>>>    }
>>>    
>>>    // do some other stuff
>>> 
>>>   ++it;
>>> }
>>> 
>>> The Image::GetPixel() method is quite time-consuming and therefore I look for a more efficient method
>>> to implement this code (without writing four different versions).
>>> 
>>> Any suggestions?
>>> 
>>> Best regards,
>>> Jan
>>> 
>>> On 03/11/2014 06:12 AM, Matt McCormick wrote:
>>>> Hi Jan,
>>>> 
>>>> To iterator through an Image or VectorImage, use the Iterators as described in the Software Guide [1]
>>>> 
>>>> HTH,
>>>> Matt
>>>> 
>>>> [1] http://itk.org/ItkSoftwareGuide.pdf
>>>> 
>>>> 
>>>> On Thu, Mar 6, 2014 at 8:23 AM, Jan Ehrhardt <ehrhardt at imi.uni-luebeck.de> wrote:
>>>> Hi folks,
>>>> 
>>>> I want to iterate through a vector image without an iterator. My approach was:
>>>> 
>>>>     MultiChannelImageType::AccessorType accessor = pImage->GetPixelAccessor();
>>>>     MultiChannelImageType::InternalPixelType* pBuffer = pImage->GetBufferPointer();
>>>> 
>>>>     for( OffsetValueType i = from; i < to; ++i )
>>>>     {
>>>>         vecPixel = accessor.Get(*pBuffer, i);
>>>>     }
>>>> 
>>>> but the results are not correct (see bug(?) below). If the bug(?) in DefaultVectorPixelAccessor is corrected ( m_OffsetMultiplier = l ) the behaviour of standard itk iterators change. I assume, I don't understand the parameters of DefaultVectorPixelAccessor::Get() correctly.
>>>> How can I use the DefaultVectorPixelAccessor correctly?
>>>> 
>>>> best,
>>>> jan
>>>> 
>>>> 
>>>> On 03/06/2014 12:25 PM, Jan Ehrhardt wrote:
>>>> Hi folks,
>>>> 
>>>> there is a bug in DefaultVectorPixelAccessor (ITK 4.4.0):
>>>> 
>>>>   void SetVectorLength(VectorLengthType l)
>>>>   {
>>>>     m_VectorLength = l;
>>>>     m_OffsetMultiplier = ( l - 1 );
>>>>   }
>>>> 
>>>>   DefaultVectorPixelAccessor(VectorLengthType l)
>>>>   {
>>>>     m_VectorLength = l;
>>>>     m_OffsetMultiplier = l - 1;
>>>>   }
>>>> 
>>>> OffsetMultiplier should be m_OffsetMultiplier = l;
>>>> 
>>>> Best regards,
>>>> Jan
>>>> 
>>>> 
>>>> _______________________________________________
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>>>> 
>>> 
>>> _______________________________________________
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>> 
> 

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