[Insight-users] Fwd: reading jpg files

[Julien Jomier]

Hi Jie,

Welcome to ITK!

Couple of comments regarding your code.

1) You don't have to allocate the image when the image is produced by a
reader (the reader is allocating the memory and setting the regions, etc...)

2) You need to do a "reader->Update();" before trying to access the image.

3) Is your JPEG image RGB? if this is the case, you should change your
ImageType to be:

    typedef itk::RGBPixel<unsigned char> PixelType;
    typedef itk::Image<PixelType,2>            ImageType;

4) GetPixel() is very slow when accessing the pixel value of an image. In
your case, you can simply do:

    std::cout << inputIt.Get() << " " << std::endl;

Hope this helps,
Let us know if you have any further problems,

Julien

> -----Original Message-----
> From: insight-users-bounces at itk.org 
> [mailto:insight-users-bounces at itk.org] On Behalf Of Jie Zhu
> Sent: Wednesday, September 15, 2004 5:35 PM
> To: insight-users at itk.org
> Subject: [Insight-users] Fwd: reading jpg files
> 
> 
> Hi All,
> I am new to itk, and I need to use it with JPEG files. I wrote a
> simple program putting the jpeg file in  image and tested to see if
> image.GetPixel() returns the correct value of the pixels. But the
> result I get looks like:
> 205
> 205
> 205
> 205
> ...
> Although the input image have a variety of pixel values, the pixel
> values GetPixel() return are all 205 or "=" if I dont convert it to
> (int). Can somebody please help me and tell me what I'm doing wrong.
> Thank you.
> Jie
> 
> Below is the code
> --------------------------------------------------------------
> -----------------------------------------------
>  typedef itk::Image<unsigned char,2>            ImageType;
> 
>  typedef itk::ImageFileReader< ImageType >  ReaderType;
> 
>  ReaderType::Pointer reader = ReaderType::New();
> 
>  const char * inputFilename  = argv[1];
>  const char * outputFilename = argv[2];
> 
>  reader->SetFileName( inputFilename  );
>  writer->SetFileName( outputFilename );
> 
>  ImageType::Pointer image = reader->GetOutput();
> 
>  //set regions in input image
>  ImageType::RegionType region;
>  ImageType::RegionType::SizeType size;
>  ImageType::RegionType::IndexType index;;
>  index[ 0 ] = 0;
>  index[ 1 ] = 0;
>  size[ 0 ] = 255;
>  size[ 1 ] = 255;
> 
>  region.SetSize( size );
>  region.SetIndex( index );
> 
>  image->SetRegions( region );
>  image->Allocate();
> 
>  //creat linear iterators
>  //typedef itk::ImageRegionConstIterator< ImageType > 
> ConstIteratorType;
> 
>  typedef itk::ImageLinearConstIteratorWithIndex< ImageType >
> ConstIteratorType;
>  ConstIteratorType inputIt( image, image->GetRequestedRegion() );
>  inputIt.SetDirection(0);
> 
>   //iteration
>  for ( inputIt.GoToBegin(); ! inputIt.IsAtEnd();
>         inputIt.NextLine())
>    {
>    inputIt.GoToBeginOfLine();
>    while ( ! inputIt.IsAtEndOfLine() )
>      {
>      ImageType::PixelType   pixelValue = image->GetPixel( indx );
>      std::cout<<(int)pixelValue<<" "<<std::endl;
>       ++inputIt;
> 
>      }
>    }
> 
> --
> Jie Zhu
> Cornell University
> 
> 
> 
> 
> -- 
> Jie Zhu
> Cornell University
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