[Insight-users] Getting unknown amount random Pixels

[N.E. Mackenzie Mackay]

Hey Luis,

	Thanks for the help.  This certainly helps.

	One question.  When trying to compile itkSetMacro( Threshold,  
PixelType ) and itkGetMacro( Threshold, PixelType ) I get a error:

	 " 'GetDebug': is not a member of  
'ImageRandomConditionalIteratorWithIndex<class itk::Image<float,3>' "

	I am assuming this because the GetDebug method is in itkObject.h which  
is not inherited by ImageRandomConditionalIteratorWithIndex.  What  
would you recommend in getting around this problem?

Thank you again,
Neilson
On Sep 12, 2004, at 5:19 PM, Luis Ibanez wrote:

>
>
> Hi Neilson,
>
>
> You can easily overcome this difficulty by taking the code of the
> Iterator, renaming the class and adding to it the functionality
> you need for evaluating the threshold.
>
>
> Please do the following:
>
>
> 1) Take the files
>
>
>    Insight/Code/Common
>
>       itkImageRandomConstIteratorWithIndex.h
>       itkImageRandomConstIteratorWithIndex.txx
>
>    and rename them as
>
>       itkImageRandomConditionalConstIteratorWithIndex.h
>       itkImageRandomConditionalConstIteratorWithIndex.txx
>
>
>
>
> 2) Edit both new files and replace all occurrences of the string
>
>       ImageRandomConstIteratorWithIndex
>
> with
>
>       ImageRandomConditionalConstIteratorWithIndex
>
>
>
>
>
> 3) At the end of the header file (extension .h) just below the line
>
>         unsigned long  m_NumberOfPixelsInRegion;
>
>     add a new member variable
>
>         IndexType   m_Threshold;
>
>
> 4)   In the current  method  Operator++()
>
>  Self & operator++()
>  {
>    this->RandomJump();
>    m_NumberOfSamplesDone++;
>    return *this;
>  }
>
> add the following the condition for checking the
> pixel value against the threshold
>
>  Self & operator++()
>  {
>    do {
>       this->RandomJump();
>       }  while( this->Get() < m_Threshold );
>     m_NumberOfSamplesDone++;
>     return *this;
>  }
>
>
>
>  With this change, every time to increment the iterator, it will
>  keep picking random samples until it finds one with value
>  above the threshold that you set.
>
>   NOTE This may take significant time if the pixels with values
>   over the threshold are not very abundant in your image.
>
>
>
> 5) Add the Set/Get methods for the Threshold by
>   inserting lines
>
>
>      itkSetMacro( Threshold, PixelType );
>      itkGetMacro( Threshold, PixelType );
>
>
>
>   6) Then in your code instantiate this new Iterator
>
>
>  typedef ImageRandomConditionalConstIreratorWithIndex<ImageType>  
> RandomIterator;
>
>  RandomIterator randIter( M_FixedImage, this->GetFixedImageRegion());
>
>  randIter.SetNumberOfSamples( TheNumberOfSamplesThatIReallyWantToGet );
>
>  randIter.SetThreshold( ThisIsMyThresholdForSelectingPixels );
>
>  randIter.GoToBegin();
>
>  // this is just in case you want to put them in an array....    
> std::vector<PixelType> myRandomPixelValuesOverThreshold;
>
>  do {
>     ++randIter;
>     myRandomPixelValuesOverThreshold.push_back( randIter.Get() );
>   } while( !randIter.IsAtEnd() );
>
>
> // At this point, the STL::Vector container has a list of // grayscale  
> values selected from randomly distributed
> // pixels, all of which have values over the threshold.
>
>
>
>
> You should read the Chapter on Image
> Iterators from the ITK Software Guide.
>
>
>    http://www.itk.org/ItkSoftwareGuide.pdf
>
>
>
>
>
>
> Regards,
>
>
>
>     Luis
>
>
> ----------------------------
>
>> ---------------------------------------------------------------------- 
>> --
>>
>> Hi,
>>
>> 	I am currently trying to get a set of N number of Pixels in a image  
>> in random locations over a set threshold.  I was attempting to use  
>> ImageRandomConstIteratorWithIndex but have come to realize that you  
>> need to set the number of samples you will be using before starting  
>> the iterator.  My problems is I don't know how many pixels I need to  
>> sample before getting N pixels over the threshold.
>>
>> Here is my code:
>>
>> 	typedef ImageRandomConstIreratorWithIndex<ImageType> RandomIterator;
>> 	RandomIterator randIter( M_FixedImage, this->GetFixedImageRegion())
>>
>> 	randIter.SetNumberOfSamples( m_NumberOfSpatialSamples );
>> 	randIter.GoToBegin();
>>
>> 	RandomIterator ::PixelType pixelValue;
>> 	
>> 	for(int i = 0; i< N; i++)
>> 	{
>> 		pixelValue = randIter.Get();
>> 		
>> 		while(PixelValue == 0)
>> 		{
>> 			++randIter;
>> 			pixelValue = randIter.Get();
>> 		}
>> 		printf("pixel value = %e \n", pixelValue);
>>
>> 		container[i] = pixelValue;
>> 	}
>>
>> 	The stuff that is printed to the screen is something like 8.61e-304
>>
>> Even when I simply try to use "get" some strange number comes out.   
>> Is it because get doesn't return a float or double but a object of  
>> some kind of container?
>>
>> Neilson
>>
>>
>> ---------------------------------------------------------------------- 
>> --
>
>
>
>