[Insight-users] logarithmic intensity transformation

[Jakub Bican]

Hi Isabelle

How to access the pixel data is described in the ITK Software Guide

    http://www.itk.org/ItkSoftwareGuide.pdf

Look for the chapter 4.1.3 "Accessing Pixel Data" (page 38).

You can also use more efficient way - iterators. See chapter 11 
"Iterators" (page 687).

Regards,
	Jakub.



Renaud Isabelle napsal(a):
> Hi Jakub,
>  
> I took a look on  your filter. However, I think there was a 
> misunderstanding.
>  
> I don't want to perform a pixel-wise log operation on my image.
>  
> Actually, I want to perform a kind of histogram transform called 
> *histogram logarithmic* to improve the contrast of my image.
>  
> So far, I performed histogram usual rescaling to transform my 
> intensities into the interval 0-255. Now, I would like my distribution 
> of gray intensities would be adjusted to improve contrast like:
>  
> f`'(x,y) = f min * (fmax / fmin) * P(f(x,y)) where P is the cumulated 
> histogram.
>  
> So adaptor will not help me, because this is an overall transform of the 
> image. Maybe I have to create my own filter but how can I access the 
> matrice of my pixel data form my image?
>  
> thanks,
>  
> Isabelle
> 
> 
> */Jakub Bican <jakub.bican at matfyz.cz>/* a écrit :
> 
> 
>     Hi Isabelle,
> 
>     logarithmic scaling can be done by these filters:
> 
>     LogImageFilter (
>     http://www.itk.org/Doxygen/html/classitk_1_1LogImageFilter.html )
>     Log10ImageFilter (
>     http://www.itk.org/Doxygen/html/classitk_1_1Log10ImageFilter.html )
> 
>     and/or adaptors:
> 
>     LogImageAdaptor (
>     http://www.itk.org/Doxygen/html/classitk_1_1LogImageAdaptor.html )
>     Log10ImageAdaptor (
>     http://www.itk.org/Doxygen/html/classitk_1_1Log10ImageAdaptor.html )
> 
>     Hope this will help you.
> 
>     Regards,
>     Jakub
> 
> 
>     Renaud Isabelle napsal(a):
> 
>      > Hi Luis,
>      >
>      > In one of your numerous posted replies, you already mentioned the
>     use
>      > of *logarithmic scaling* to improve visualisation of images.
>      >
>      > "It is not rare to use a logarithmic intensity transformation in
>     order
>      > to display the FFT output and still be able to "see" something."
>      >
>     http://public.kitware.com/pipermail/insight-users/2004-November/011201.html
>      >
>      > This is actually what I need to do to improve the quality of my
>      > ultrasonographic image.
>      >
>      > --> Could you tell me a way to perform this logarithmic scaling? Is
>      > there already a function for that, or maybe could I compute my
>     own one
>      > if you tell me how to get access of the pixel data of my image
>      > displayed with ITK and VTK.
>      >
>      > Thanks for answer,
>      >
>      > Isabelle
>      >
>      >
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