[Insight-users] Pluggable Factories

[Luis Ibanez]

Hi Bart,


Thanks for pointing this out.


We should clarify the text in the Software Guide.


Here is what happens:

1) Every new file format requires you to implement
    two classes. If the fileformat is called WWWW,
    then the classes will be called:


           itkWWWImageIO
           itkWWWImageIOFactory


2) They will derive respectively:

    itkWWWImageIO         from    itkImageIOBase
    itkWWWImageIOFactory  from    itkObjectFactoryBase**

    **All factories in ITK derive from this base factory


3) The class itkImageIOFactory, is the front end to
    all the IO factories. You can see it as a sort of
    "Dispatcher" pattern. All the actuall IO factories
    get registered with the ImageIOFactory in the file
    Insight/Code/IO/itkImageIOFactory.cxx


4) When you ask the ImageFileReader or the ImageFileWriter
    to read/write (respectively) a file. They will ask the
    ImageIOFactory to find an actual IO factory for that file
    format.

    A more appropriate name for the ImageIOFactory could
    have been:


                   "ImageIOFactoryFinder"
             or    "ImageIOFactoryCollection"
             or    "ImageIOFactoryRegistry"
             or    "ImageIOFactoryDispatcher"


     Since this class does not really create ImageIO objects
     but ImageIOFactory objects.



Please let us know if you have further questions,


   Thanks


     Luis


=================
deboeck wrote:
> Hi,
> 
>  
> 
>   The ITK book mentions on page 211 that “each time a new file format is 
> added (i.e. a new ImageIO subclass is created), a factory must be 
> implemented as a derived class of the ImageIOFactory class”.
> 
>   The PNGImageIO and PNGImageIOFactory types in ITK, however, are 
> derived from ImageIOBase and ObjectFactoryBase respectively. How does 
> this relate ?
> 
>  
> 
> Thanks,
> 
> Bart
> 
> 
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