[ITK-users] How to determine PixelType of itk::Image

Dženan Zukić dzenanz at gmail.com
Tue Mar 15 15:49:01 EDT 2016 

Hi Lambert,

a 'general' interface cannot be made. You are not the first to face this
issue. One way is to do if/else for all the supported cases. Another way is
to define some template function or helper class, and then let compiler
take care of type matching. But indeed, the code is either bloated (version
one) or somewhat exotic (version two).

RGB image can be stored either way. You can have itk::Image<char,3> with 3
dimensions x,y,color (consecutive color planes) or
itk::Image<itk::RGBPixel<char>, 2> (consecutive triplets). It depends on
your treatment. I believe that consecutive triplets is more common.

Regards,
Dženan

On Tue, Mar 15, 2016 at 3:39 PM, Lambert Zijp <ljzijp at gmail.com> wrote:

> Hi Dženan,
>
> Haha, true enough, ItkToAvs would have to return an errorcode
> 'unsupported'. Yes, pixelspacing and origin can be retrieved. Also the
> size of each dimension, though that took me a while: it was well hidden.
> Still, it is very frustrating that it cannot be determined from itk::image
> whether it is an ordinary, commonly occurring image like an BGR ARGB or a
> 3-vector float image.
> At least, that is what I gather from your answer: a 'general' interface to
> other image processing libraries cannot be made!
>
> Am I the first person having problems with this?
> How is an RGB image stored in itk, as consecutive triplets or as
> consecutive color-planes.
>
> Greetings,
> Lambert
>
> On Tue, Mar 15, 2016 at 7:57 PM, Dženan Zukić <dzenanz at gmail.com> wrote:
>
>> Yes, it knows. Using something like this:
>>
>> template <typename ImageType>
>> void ItkToAvs(AVSfield** ppAvs, typename ImageType::Pointer image)
>> {
>> typename ImageType::PixelType *pixelPointer=image->GetBufferPointer();
>> unsigned int dimension=ImageType::ImageDimension;
>> //the rest of conversion code
>> }
>>
>> However, ImageType::PixelType can be arbitrary type. Consider this:
>> class myClass {int a; complex<double> c; string sRep;};
>> typedef itk::Image<myClass, 2> ImageType;
>> ItkToAvs(ppAvs, image);
>>
>> What do you expect ItkToAvs to do?
>>
>> Regards,
>> Dženan
>>
>> On Tue, Mar 15, 2016 at 2:53 PM, Lambert Zijp <ljzijp at gmail.com> wrote:
>>
>>> This is all very confusing to me. In the FileWriter example, the caller *already
>>> knows* what the IOComponentType
>>> <http://www.itk.org/Doxygen/html/classitk_1_1ImageIOBase.html#a8dc783055a0af6f0a5a26cb080feb178> and
>>> what the IOPixelType
>>> <http://www.itk.org/Doxygen/html/classitk_1_1ImageIOBase.html#abd189f096c2a1b3ea559bc3e4849f658> of
>>> the itk::Image is (it is hard-coded; not retrieved from the itk::Image).
>>> The same holds for the reader: it gets that information from the file.
>>> I want to make a general function that takes *ANY* itk::Image as input,
>>> and converts it to an AVS datasructure (which supports all of them). So I
>>> need to get the information from itk::Image.
>>> Is there a way to get it from itk::Image? Or is it true that an
>>> itk::Image does not know what it actually is/represents?
>>>
>>> On Tue, Mar 15, 2016 at 7:07 PM, Dženan Zukić <dzenanz at gmail.com> wrote:
>>>
>>>> If I remember correctly, using this
>>>> <http://www.vtk.org/Wiki/ITK/Examples/IO/ReadUnknownImageType>
>>>> approach you can also get number of components with something like:
>>>> imageIO->GetNumberOfComponents();
>>>> You can take a look at class documentation
>>>> <http://www.itk.org/Doxygen/html/classitk_1_1ImageIOBase.html> for
>>>> more details.
>>>>
>>>> On Tue, Mar 15, 2016 at 1:09 PM, Lambert Zijp <ljzijp at gmail.com> wrote:
>>>>
>>>>> I'm still not sure how to handle vector images. Dženan gave an
>>>>> example of an RGB image. That would be a 3-vector unsigned char pixeltype.
>>>>> Would I have to write out in those *'if  **(**typeid(ValueType) ==
>>>>> ???)'* statements all permutations of the number of vectors and the
>>>>> type? Or is there a way to separate the number of vectors and the pixeltype?
>>>>> How are vector images stored in memory in ITK. In an RGB image for
>>>>> example, are the pixels consecutive triplets, or is the image stored as
>>>>> three consecutive color planes?
>>>>> I'm particular interested in 3D displacement vector fields, that are
>>>>> the result of deformable registration.
>>>>>
>>>>>
>>>>> On Tue, Mar 15, 2016 at 5:22 PM, Bill Lorensen <
>>>>> bill.lorensen at gmail.com> wrote:
>>>>>
>>>>>> This example may help
>>>>>> http://www.vtk.org/Wiki/ITK/Examples/IO/ReadUnknownImageType
>>>>>> On Mar 15, 2016 8:44 AM, "Dženan Zukić" <dzenanz at gmail.com> wrote:
>>>>>>
>>>>>>> Of course it complained, switch statement is for integral types (if
>>>>>>> I remember correctly).
>>>>>>>
>>>>>>> Regards
>>>>>>>
>>>>>>> On Tue, Mar 15, 2016 at 11:39 AM, Lambert Zijp <ljzijp at gmail.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> Hi Dženan,
>>>>>>>>
>>>>>>>> Thank you very much!
>>>>>>>> Visual Studio 9 does not recognize decltype(), but typeid() worked
>>>>>>>> fine. At least, when you make separate if statements, like you did in your
>>>>>>>> example. When tried to use it in a switch statement, the compiler
>>>>>>>> complained.
>>>>>>>>
>>>>>>>> Greetings,
>>>>>>>> Lambert
>>>>>>>>
>>>>>>>>
>>>>>>>> On Tue, Mar 15, 2016 at 2:47 PM, Dženan Zukić <dzenanz at gmail.com>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>> Hi Lambert,
>>>>>>>>>
>>>>>>>>> the classic way is using a bunch of if-else's.
>>>>>>>>>
>>>>>>>>> if (decltype(ValueType)==decltype(int))
>>>>>>>>> {
>>>>>>>>> //int specific processing
>>>>>>>>> }
>>>>>>>>> else if (decltype(ValueType)==decltype(itk::RGB<char>))
>>>>>>>>> {
>>>>>>>>> //RGB<char> specific processing
>>>>>>>>> }
>>>>>>>>> ​else if ...​
>>>>>>>>>
>>>>>>>>> ​If you can't use C++11's decltype then use typeid from
>>>>>>>>> <typeinfo>​ header.
>>>>>>>>>
>>>>>>>>> Regards,
>>>>>>>>> Dženan
>>>>>>>>>
>>>>>>>>> On Tue, Mar 15, 2016 at 5:48 AM, Lambert Zijp <ljzijp at gmail.com>
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>> I want to write a function that converts an arbitrary ITK image
>>>>>>>>>> to another format (AVS in my case).
>>>>>>>>>> It has been suggested that following functionprototype could de
>>>>>>>>>> the job:
>>>>>>>>>> template<typename ValueType,unsigned int Dimension>
>>>>>>>>>> int ItkToAvs(AVSfield** ppAvs, typename
>>>>>>>>>> itk::Image<ValueType,Dimension>::Pointer pItkImage);
>>>>>>>>>>
>>>>>>>>>> Now I want to know whether ValueType equals unsigned char or
>>>>>>>>>> short or int etc. Also whether the pixels are single numbers or vectors.
>>>>>>>>>> How does one do that?
>>>>>>>>>>
>>>>>>>>>> Greetings,
>>>>>>>>>> Lambert
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
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>>> Visit other Kitware open-source projects at
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