[Insight-users] FFTImageFilter

[Markus Neuner]

I just looked at the code in the example and all seems working (at
leasts for me).
What do you expect as output?
Change the "WriteImageType" to float or double and try it again.
Open the image with paraview, imagej or any other suited image viewer.
It may be useful to take the log of the real and complex images for a
better contrast.

On 04.08.2010 21:45, Ming Chao wrote:
> float
>
> On Wed, Aug 4, 2010 at 2:38 PM, Markus Neuner <neuner.markus at gmx.net
> <mailto:neuner.markus at gmx.net>> wrote:
>
>     What is the pixel type of "ImageType"?
>
>
>     On 04.08.2010 21:11, Ming Chao wrote:
>>     I checked the complex image FFT created from the input image was
>>     fine. Also I checked the real and imaginary parts in floating
>>     point format, respectively. They both are fine. The problem
>>     started to happen when rescaling the real/imaginary image into an
>>     interger-type image. Here is part of the rescaling code:
>>
>>       typedef unsigned char WritePixelType;
>>       typedef itk::Image< WritePixelType, Dimension > WriteImageType;
>>      
>>       typedef itk::RescaleIntensityImageFilter<ImageType,
>>     WriteImageType > RescaleFilterType;
>>
>>       RescaleFilterType::Pointer intensityRescaler =
>>     RescaleFilterType::New();
>>       intensityRescaler->SetOutputMinimum(  0  );
>>       intensityRescaler->SetOutputMaximum( 255 );
>>      
>>       intensityRescaler->SetInput( realFilter->GetOutput() );
>>
>>       typedef itk::ImageFileWriter< WriteImageType > WriterType;
>>       WriterType::Pointer writer = WriterType::New();
>>       writer->SetFileName( argv[2] );
>>       writer->SetInput( intensityRescaler->GetOutput() );
>>
>>       try
>>         {
>>     writer->Update();
>>         }
>>       catch( itk::ExceptionObject & excp )
>>         {
>>     std::cerr << "Error writing the real image: " << std::endl;
>>     std::cerr << excp << std::endl;
>>     return EXIT_FAILURE;
>>         }
>>
>>       typedef itk::ImageRegionConstIterator< WriteImageType >
>>     ConstIteratorType;
>>       WriteImageType::Pointer RealImage = intensityRescaler->GetOutput();
>>       ConstIteratorType in( RealImage, RealImage->GetRequestedRegion() );
>>       
>>       for ( in.GoToBegin(); !in.IsAtEnd(); ++in )
>>       {
>>      std::cout << in.Get() << std::endl;
>>       }
>>
>>
>>     From the output I got all zeros....Apparently something wrong
>>     with the rescaler. Could anybody take a look? Thanks very much,
>>
>>     Ming
>>
>>
>>     On Wed, Aug 4, 2010 at 9:35 AM, Ming Chao <mingchao2005 at gmail.com
>>     <mailto:mingchao2005 at gmail.com>> wrote:
>>
>>         I tried to run FFTImageFilter.cxx to do an FFT of an image.
>>         The input image is a 512x512, 24 bit thoracic CT image in jpg
>>         format. The output of the example cxx code are the real and
>>         imaginary parts of FFT of the input image. However, when I
>>         look at the two output images, they are just uniformly
>>         grey/black, depending on 
>>
>>           intensityRescaler->SetOutputMinimum(  0  );
>>           intensityRescaler->SetOutputMaximum( 255 );
>>
>>         in the code. What did I do wrong? Many thanks,
>>
>>         Ming
>>
>>
>>
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