[Insight-users] logarithmic scaling

[Renaud Isabelle]

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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