[Insight-users] logarithmic intensity transformation

[Renaud Isabelle]

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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