[Insight-developers] ImageBase->CopyInformation: Number of components per pixel copied

[Luis Ibanez]

Hi Stephen,


There seem to be a bug in your code.
Both print outs are from the VectorImage.


Your second print out:


 >   std::cout << "Char # of comp = "
 >             << myVectorImage->GetNumberOfComponentsPerPixel( )
 >             << std::endl;



should probably be:


 >   std::cout << "Char # of comp = "
 >             << myCharImage->GetNumberOfComponentsPerPixel( )
 >             << std::endl;




   Luis



-----------------------------
Stephen R. Aylward wrote:
> Hi,
> 
> The code below illustrates the problem.
> 
> That code does the following:
> 1) Creates a vector image, sets the number of components per pixel, and 
> prints the number of components per pixel.
> 2) Creates a "normal" (non-vector) image, calls CopyInfo passing the 
> vector image, and prints the number of components per pixel.
> 
> The result is that the number of components per pixel of the 
> itk::Image<char, 3> image is reported as 3.
> 
> Should we document, only call SetNumberOfComponents in CopyInfo if the 
> image is a vectorimage, or other?
> 
> Thanks,
> Stephen
> 
> 
> #include "itkImage.h"
> #include "itkVectorImage.h"
> 
> int main(int argc, char **argv)
>   {
>   // Create a vector image
>   typedef itk::VectorImage< char, 3 > VectorImageType;
>   VectorImageType::Pointer myVectorImage = VectorImageType::New();
>   myVectorImage->SetNumberOfComponentsPerPixel( 3 );
> 
>   VectorImageType::SizeType size;
>   size[0] = 25;
>   size[1] = 25;
>   size[2] = 25;
>   myVectorImage->SetRegions( size );
> 
>   VectorImageType::SpacingType spacing;
>   spacing[0] = 1;
>   spacing[1] = 2;
>   spacing[2] = 3;
>   myVectorImage->SetSpacing(spacing);
> 
>   myVectorImage->Allocate();
> 
>   std::cout << "Vector # of comp = "
>             <<  myVectorImage->GetNumberOfComponentsPerPixel( )
>             << std::endl;
> 
>   // Create a char image and copy vector images's info
>   typedef itk::Image< char, 3 > CharImageType;
>   CharImageType::Pointer myCharImage = CharImageType::New();
>   myCharImage->SetRegions( myVectorImage->GetLargestPossibleRegion() );
>   myCharImage->CopyInformation( myVectorImage );
>   myCharImage->Allocate();
> 
>   std::cout << "Char # of comp = "
>             << myVectorImage->GetNumberOfComponentsPerPixel( )
>             << std::endl;
>   }
> 
> 
> Luis Ibanez wrote:
> 
>>
>> Hi Stephen,
>>
>> That's a good point.
>>
>> Notice that yet nothing prevents you from changing the number of
>> components of the recipient image in the GenerateData() method
>> of your filter, before you fill in the content of the output
>> image.
>>
>> Note also, that in practice, the SetNumberOfComponentsPerPixel()
>> method only performs a real action when it is invoked in an
>> itkVectorImage.   In any other case, ITK images have compile-time
>> defined number of components per pixel and the call is simply
>> ignored.
>>
>> Are you dealing with a filter that produces an itkVectorImage
>> as output  ?
>>
>>
>>      Luis
>>
>>
>>
>> --------------------------
>> Stephen R. Aylward wrote:
>>
>>> Hi,
>>>
>>> The CopyInformation function of ImageBase sets largestPossibleRegion, 
>>> Spacing, Origin, Directions...all good.
>>>
>>> However, it also sets NumberOfComponentsPerPixel.   Perhaps this is 
>>> inappropriate since it is not necessary for the images to have the 
>>> same pixel type for CopyInformation to work.  Perhaps 
>>> NumberOfComponentsPerPixel is conceptually a pixel-type-specific 
>>> piece of information.   Admittedly this is arguable, but consider a 
>>> filter that has a vector image as input and outputs a scalar 
>>> image...we cannot use the CopyInformation command.
>>>
>>> Of course, the point is perhaps moot given the need for backward 
>>> compatibility...I cannot think of a backward-compatible solution 
>>> beyond better documentation.
>>>
>>> Stephen
>>>
>>
>