[Insight-users] logarithmic scaling

[Jakub Bican]

Hi Isabelle,

you should add 1 to all image values after Abs filter and before Log 
filter. This can be done by

       AddImageAdaptor 
(http://www.itk.org/Doxygen/html/classitk_1_1AddImageAdaptor.html)

which enables you to add a constant value to all image pixels. The value 
can set via SetValue() method of the adaptor class. Log filter will then 
produce no "infinities" as you skip "problematic" interval <0,1).


HTH,
          Jakub



Renaud Isabelle napsal(a):

> Hi,
>  
> I'm still triing to improve the quality of visualization of raw data.
>  
> - by computing *absolute value* of raw data, my displayed images are 
> too *dark*.
>  
> - by applliing a *log scaling* after abs(), my displayed data are now 
> too *bright*. That's the reason why:
>       after having taken a look on *LogImageFilter* and 
> *LogImageAdaptor*, it seems that *the case where input data = 0* is 
> not dealed with: log(x=0) returns a very big negative value equivalent 
> to -infinite. So, when I applied a linear *rescaling* between 0 and 
> 255, my rescaled data is in [-infinite, alpha]. 
>  
> Here is why I did:
>  
> *absFilter->SetInput( imageInitiale );*
> *logFilter->SetInput( absFilter->GetOutput() );
> rescaleFilter->SetInput( logFilter->GetOutput()) ;*
>
> ** 
>
> So I'm triing to implement my own *logImageAdaptor* to deal with the 
> case where my input data is null.
>
> class LogPixelAccessor
> {
> public:
>  typedef short InternalType;
>  typedef short ExternalType;
>
> ExternalType Get( const InternalType & input ) const
> {
>
>       return ( (input != 0) ? (ExternalType)log((double)input) : 0 );
>
> }
> };
>
> But I'm always having an error at execution that I can't solve: the 
> debugger says error encounterd is in Set function of 
> DefaultPixelAccessor  class.
>
> class ITK_EXPORT DefaultPixelAccessor 
> {
> public:
>
>  /** External typedef. It defines the external aspect
>    * that this class will exhibit. */
>   typedef TType ExternalType ;
>
>   /** Internal typedef. It defines the internal real
>    * representation of data. */
>   typedef TType InternalType ;
>
>  * /** Set the pixel. */
>   inline void Set(TType & output, const TType & input) const
>     {output = input;}*
>
> --> Could anybody tell me why?
>
> isabelle
>
> */Kuba Bican <kuba at smyslzivota.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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