[Insight-users] HELP! A "magic" bug bites me.

[Luis Ibanez]

Hi Michael,
Thanks for the update.

When you installed the Gremlin detectors,
I assume that you found that the

* Size (in pixels)
* Origin
* Spacing

of both the read Dicom image and the processed threshold image
were the same.

Can you confirm this ?



Gremlins are very vicious creatures, and if they know that you are
a C# or Java developer who is adventuring into the C++ heaven,
they will do whatever it takes to hold you back and force you to
live in darkness.

Here are some simple C++ rules:

1) Leave no variables uninitialized

2) Use ITK Smart Pointers

3) Use defensive programming techniques
    (e.g. check for everything, even what seems to be obvious,
    Gremlins love to fiddle with the aspects of your code that
    you trust the most).


The main suspect here is the m_DicomReader class....


Tell us more about it....


Are you , by any chance, using the vtkKWImageIO classes ?


if so, are you using a smart pointer for holding this variable ?


Also,  typical trace of Gremlin wizardry is that your code may
do the right thing when run in Debug, and then fail, when run
in Release. (particularly when you have uninitialized variables).


        Be brave and stick to your C++ aspirations.


The path may be hard,
but the rewards are proportional to the suffering.


     Regards,


           Luis


-------------------------------
On Mon, Aug 17, 2009 at 12:07 PM, Michael Xanadu <
xanadu.michael at googlemail.com> wrote:

> Hi Luis,
>
> thank you for your quick reply. You're right, usually I'm a C# & Java
> programmer and I'm into C++/VTK/ITK for just a few weeks. Do you really
> think my problems lies in uninitialized variables?
> I already used your "gremlin detectors" earlier, the m_Dicomreader works
> fine and the thresholder always produces a black output (all pixels are
> zero). But I think the problem really is C++ (not ITK), too. What do you
> think should I do? Are there special rules, when using ITK in C++ (for
> example, should I initialize my pipelines in a special way or something?)
> Are there some important C++ topics I should know about?
>
> Regards, Michael
>
>
>
> 2009/8/17 Luis Ibanez <luis.ibanez at kitware.com>
>
>
>> Hi Michael,
>>
>>                             This is clearly the work of Gremlins!
>>
>>
>> Here are some of the typical mechanisms used by Gremlins to exasperate C++
>> developers
>> with the evil hope of making adopt C# or Java:
>>
>>
>>    - Distract the C++ developer to make her/him leave some uninitialized
>>    variables
>>    (You can check for uninitialized variables by using Valgrind)
>>
>>    - Gremlins may have removed from your m_DicomReader class the code
>>    that
>>    triggers the read of the DICOM image, so that when you call
>>    GetITKImage()
>>    you get an empty image.
>>
>>
>> You can install Gremlin detectors by adding a couple of lines:
>>
>>
>>    - m_Dicomreader->GetITKOutput()->Print( std::cout );
>>    before you set the image to the threshold filter
>>
>>    - thresholder->GetOutput()->Print( std::cout )
>>    after you call Update in the connected threshold filter.
>>
>>
>>
>>    Regards,
>>
>>
>>          Luis
>>
>> ---------------------------
>> On Mon, Aug 17, 2009 at 5:26 AM, Michael Xanadu <
>> xanadu.michael at googlemail.com> wrote:
>>
>>> Hallo itk users,
>>>
>>> now take a look at some real strange bug. I programmed a
>>> ConnectedThresholdImageFilter, which works (surprisingly).
>>> But if add add some lines of QT code into the method (which don't mess
>>> with the filter) - all I get is a black output!
>>> This kind of bug has happened to me a lot lately. Sometimes a filter
>>> doesn't seem to work, I tinker around with it for a day and after the SAME
>>> code works!
>>> I even have a fast marching filter which only works, if I add some lines
>>> in which I create some itk::ImageFileWriter objects (BUT I DON'T USE THEM!).
>>> And once I get a code to work, it only works in the current
>>> method/class/project. If I copy and paste the code -> black ouput!
>>> Do Someone know, what went wrong?
>>>
>>> Thanx in advance, Michael
>>>
>>>
>>>
>>> void MyMainWindow::connectedThresholdFilter()
>>> {
>>>     typedef itk::ConnectedThresholdImageFilter<ImageType, ImageType>
>>> ThresholderType;
>>>     ThresholderType::Pointer thresholder = ThresholderType::New();
>>>     thresholder->SetInput( m_Dicomreader->GetITKOutput() );
>>>
>>>     // if I uncomment following line, I get a black output !!!!
>>>     //QString s1 = this->qlineedit1->text();
>>>
>>>     thresholder->SetLower(0);
>>>     thresholder->SetUpper(800);
>>>     ImageType::IndexType  index;
>>>     index[0] = 250;
>>>     index[1] = 250;
>>>     thresholder->SetSeed(index);
>>>     thresholder->SetReplaceValue(255);
>>>
>>>     try
>>>     {
>>>         thresholder->Update();
>>>     }
>>>     catch( itk::ExceptionObject & excep )
>>>     {
>>>         std::cerr << "Exception caught !" << std::endl;
>>>         std::cerr << excep << std::endl;
>>>     }
>>>
>>>     // Here I use a vtkImageViewer2 to show the output
>>>     Utility::popUpImage(thresholder->GetOutput());
>>> }
>>>
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>>
>
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