[Insight-users] absolute value and Hilbert transform

[Gavin Baker]

Bonjour Isabelle,

On Tue, May 24, 2005 at 07:43:21PM +0200, Renaud Isabelle wrote:

> I am working on RF images. In order to visualize these ones, I have
> to compute the absolute value of the image and then rescale image
> data.
>
> I am wondering if there is already an ITK function adapted to
> calculate the absolute value of an image. Or should I use abs()
> function of math library in C?

Yes, ITK has a filter to calculate the absolute value per-pixel.  It
is one of many unary functors, as described here:

  http://www.itk.org/Doxygen/html/classitk_1_1AbsImageFilter.html

You may also be interested in these filters (for the rescaling):

  http://www.itk.org/Doxygen/html/classitk_1_1RescaleIntensityImageFilter.html
  http://www.itk.org/Doxygen/html/classitk_1_1ShiftScaleImageFilter.html
  http://www.itk.org/Doxygen/html/classitk_1_1IntensityWindowingImageFilter.html

> In future, I would have to transform RF images in B-mode images for
> a better visualization. This is by computing the absolute value of
> the Hilbert transform of RF image data. Is it also an ITK Hilbert
> transform already computed?

ITK doesn't currently provide such a filter (AFAIK).  The Software
Guide has a section on writing new filters, and you should be able to
base your new filter on an existing filter (most likely starting with
ImageToImageFilter).  The VNL library has quite a comprehensive matrix
math library, which should provide what you need for the implementation.

Good luck,

  :: Gavin

-- 
Gavin Baker                                      Complex Systems Group
http://www.cs.mu.oz.au/~gavinb             The University of Melbourne