[Insight-users] X-ray flat field correction filter

[Robert.Atwood at diamond.ac.uk]

Hi,

I've created a filter for applying the simple (S-D)/(F-D) correction that we use for eliminating the effect of spatial variation in the incoming beam intensity; I didn't find such a filter present already ; but I simply copied TernaryAddImageFilter and changed the formula (and the name). However I did this without understanding how it works; the functor is defined in the header file but nowhere can I find where the functor is actually set in the class that is derived from the parent TernaryFunctorImageFilter class . (i.e. the call to SetFunctor(), where is it?) I suppose this is done by some clever trick.

It does, however, appear to work.

I did not incorporate any rescaling or casting of data types into the filter, so this must be done in a pipeline if using the filter with e.g. ushort data and expecting useful results (because the result of the division will usually be between 0 and 1, so the filter will work fine and return 0 everywhere except where noise has caused the image 'S' to have a greater value than 'F' or less than 'D' ) I think keeping it simple is best and doing the required transformations. 
For example, I may have 1000 images for which I wish to apply the same F and D, but I want to use these in a tomo reconstruction and so I don't want independant rescaling based on each image's contents. My first test applet thus applies the filter for one image, then runs the output through RescaleIntensityImageFilter, calls the Get*() functions , applys a little margin and sets the factors for IntensityWindowingFilter to apply to each of the images in the set. Other applications might require a different approach i.e. automatic scaling to each image's range might be desirable.

Would it be useful to contribute these (albeit minor) modifications , I've called it TernaryFlatcorrImageFilter;  or is this already in the library and I've missed it?
 
(I suppose one could have used the parent class, defined a functor and used SetFunctor, but actually copying TernaryAdd and modifying it seemed easier!)

Regards
Robert


 54 /** \class TernaryFlatcorrImageFilter
 55  * \brief Pixel-wise flat field correction using three images.
 56  *
 57  * Applying the formula I = ( (S-D) / (F-D))
 58  * where input1 is S (signal i.e input image)
 59  *       input2 is F (Flat or White Field Image)
 60  *       input3 is D (Dark field image)
 61  *       GetOutput() returns I (corrected Intensity)

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