[Insight-users] native function returning an itk::Image

[namgyun Lee]

On Sun, Aug 31, 2008 at 10:56 PM, namgyun Lee <ggang56 at gmail.com> wrote:

> I have a further question about this.
>
> Let me describe the situation briefly.
>
> I have defined all types in the header file of class and also defined a
> private member variable "list" as std::vector<ImageType::Pointer>.
> And I return the ImageType::Pointer to the "list" using two different
> methods,
>
> 1) list.push_back(this->readImg("brain.dcm"));
> 2)ImageType::Pointer myImage = this->readImg("brain.dcm");
>   list.push_back(myImage);
>
> My question is what is the difference between the methods describe above?
> Could you explain the difference emphasizing the scope and reference
> counting perspective?
>
>
> Thank you so much.
>
> Sincerely,
> Namgyun Lee
>
>
>
>
> On Sun, Aug 31, 2008 at 7:56 AM, Luis Ibanez <luis.ibanez at kitware.com>wrote:
>
>>
>> Hi Protein,
>>
>>
>> In order to keep an ITK image alive when returning it from
>> a function, you *MUST* return it as a SmartPointer.
>>
>> Instead of your current signature:
>>
>>     ImageType* readImg(char* imageFileName);
>>
>> You should use
>>
>>    ImageType::Pointer readImg(char* imageFileName);
>>
>>
>> In that way the smart pointer will be copied in the stack when
>> the function is returning, and that temporary copy wil keep the
>> image alive long enough to survive the destruction of data in
>> the local scope of the function.
>>
>> Make sure that the returned variable is assigned to a
>> SmartPointer as well.
>>
>>
>> That is, when you call the function do something like:
>>
>>   ImageType::Pointer myImage = readImg("brain.dcm");
>>
>>
>> NOTE: You *do not* need, and you *should not* modify the
>>      reference counting of ITK images. SmartPointers
>>      are supposed to do that for you.
>>
>>
>>
>>  Regards,
>>
>>
>>      Luis
>>
>>
>> ---------------
>>
>> protein wrote:
>>
>>> Hey all,
>>>
>>> This might be a duplicated question but I really didn't find a answer..
>>>
>>> Basically my scenario could be described as to write a native function
>>> to read a .png file, using an instantiated itk::ImageFileReader<unsigned
>>> char>,
>>> and return an itk::Image<unsigned char>. How to keep that itk::Image
>>> alive
>>> after returning from the native function?
>>>
>>> So in the header file I defined:
>>>
>>>   const    unsigned int    Dimension = 2;
>>>   typedef  float           PixelType;
>>>   typedef itk::Image< PixelType, Dimension >  ImageType;
>>>   typedef itk::ImageFileReader< ImageType  > ImageReaderType;
>>>
>>> then I declear a function, which takes
>>> char* imageFileName as input
>>> and
>>> output an ImageType*
>>>
>>>    ImageType* readImg(char* imageFileName);
>>>
>>> the definition readImg function:
>>>    ImageReaderType reader = ImageReaderType::New();
>>>    reader->SetFileName(imageFileName);
>>>    reader->Update();
>>>    return reader->GetOutput();
>>>
>>>
>>> But when calling this function in main(), by:
>>>    ImageType::Pointer img = readImg("test.png");
>>>
>>> I know the reader is destructed when going back to main, thus the
>>> there will be error.
>>>
>>> So I increased the reference count of reader before returning,
>>> to keep it alive even after returned from the readImg function, I added:
>>>    reader->SetReferenceCount(1+reader->GetReferenceCount());
>>> before "return reader->GetOutput();"
>>>
>>> Then in the main, I could use the img.
>>>
>>> However this seems not that nice to me since reader won't get
>>> released....
>>>
>>>
>>> Could anyone tell me in general how to deal with such kind of problems?
>>> I really appreciate that!
>>>
>>> Thanks,
>>> Yi
>>> _______________________________________________
>>> Insight-users mailing list
>>> Insight-users at itk.org
>>> http://www.itk.org/mailman/listinfo/insight-users
>>>
>>>  _______________________________________________
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>>
>
>
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