ITK/Examples/Images/ConvertPixelBuffer

This example shows how to convert an RGBAImage to an RGBImage using ConvertPixelBuffer::Convert. ConvertPixelBuffer is used internally in itkImageFileReader to convert raw data into itk Images.

NOTE: This example accesses internal pointers for pixel container data. If you think you need to use this approach, be extremely careful. Since you are dealing with raw pointers, you must be certain that the memory organization for the input and output is compatible in C++ type and dimensions.

A safer approach uses itkCastImageFilter as illustrated in this example: CastImageFilter

ConvertPixelBuffer.cxx

<source lang="cpp">

1. include "itkRGBPixel.h"
2. include "itkRGBAPixel.h"
3. include "itkImage.h"
4. include "itkDefaultConvertPixelTraits.h"
5. include "itkConvertPixelBuffer.h"
6. include "itkImageRandomConstIteratorWithIndex.h"

int main(int, char*[]) {

 const int xDimension = 200;
 const int yDimension = 100;

 typedef unsigned char                  ComponentType;
 typedef itk::RGBPixel<ComponentType>   RGBPixelType;
 typedef itk::RGBAPixel<ComponentType>  RGBAPixelType;
 typedef itk::Image< RGBPixelType, 2 >  RGBImageType;
 typedef itk::Image< RGBAPixelType, 2 > RGBAImageType;
 typedef itk::DefaultConvertPixelTraits< RGBPixelType >
                                        TraitsType;
 typedef itk::ConvertPixelBuffer< ComponentType, RGBPixelType, TraitsType >
                                        RGBAConverterType;

 RGBImageType::Pointer rgbImg   = RGBImageType::New();
 RGBAImageType::Pointer rgbaImg = RGBAImageType::New();

 // Create the two images
 // RGBAImage
 RGBAImageType::IndexType rgbaStart;
 rgbaStart[0] = 0;
 rgbaStart[1] = 0;

 RGBAImageType::SizeType rgbaSize;
 rgbaSize[0] = xDimension;
 rgbaSize[1] = yDimension;

 itk::ImageRegion<2> rgbaRegion(rgbaStart,rgbaSize);
 rgbaImg->SetRegions(rgbaRegion);
 rgbaImg->Allocate();

 RGBAPixelType rgbaDefault;
 rgbaDefault[0] = 127;
 rgbaDefault[1] = 100;
 rgbaDefault[2] = 230;
 rgbaDefault[3] = 255;
 rgbaImg->FillBuffer(rgbaDefault);

 // RGBImage
 itk::ImageRegion<2>     rgbRegion = rgbaRegion;
 rgbImg->SetRegions(rgbRegion);
 rgbImg->Allocate();

 size_t numberOfPixels =
   rgbImg->GetLargestPossibleRegion().GetNumberOfPixels();

 // Convert a raw buffer to a buffer of pixel types
 RGBAConverterType::Convert(
   rgbaImg->GetBufferPointer()->GetDataPointer(),
   rgbaImg->GetNumberOfComponentsPerPixel(),
   rgbImg->GetBufferPointer(),
   numberOfPixels);

 // Check a few random values
 itk::ImageRandomConstIteratorWithIndex<RGBImageType>
   rgbIterator(rgbImg, rgbImg->GetLargestPossibleRegion());
 rgbIterator.SetNumberOfSamples(numberOfPixels / 10);
 rgbIterator.GoToBegin();
 
 while(!rgbIterator.IsAtEnd())
   {
   if (rgbImg->GetPixel(rgbIterator.GetIndex())[0] !=
       rgbaImg->GetPixel(rgbIterator.GetIndex())[0] ||

       rgbImg->GetPixel(rgbIterator.GetIndex())[1] !=
       rgbaImg->GetPixel(rgbIterator.GetIndex())[1] ||

       rgbImg->GetPixel(rgbIterator.GetIndex())[2] !=
       rgbaImg->GetPixel(rgbIterator.GetIndex())[2])
     {
     std::cout << "Copy failed for index " << rgbIterator.GetIndex()
               << " got " << rgbImg->GetPixel(rgbIterator.GetIndex())
               << " but expected " << rgbaImg->GetPixel(rgbIterator.GetIndex())
               << std::endl;
     }
   ++rgbIterator;
   }
 return EXIT_SUCCESS;

} </source>

CMakeLists.txt

<syntaxhighlight lang="cmake"> cmake_minimum_required(VERSION 3.9.5)

project(ConvertPixelBuffer)

find_package(ITK REQUIRED) include(${ITK_USE_FILE}) if (ITKVtkGlue_LOADED)

 find_package(VTK REQUIRED)
 include(${VTK_USE_FILE})

endif()

add_executable(ConvertPixelBuffer MACOSX_BUNDLE ConvertPixelBuffer.cxx)

if( "${ITK_VERSION_MAJOR}" LESS 4 )

 target_link_libraries(ConvertPixelBuffer ITKReview ${ITK_LIBRARIES})

else( "${ITK_VERSION_MAJOR}" LESS 4 )

 target_link_libraries(ConvertPixelBuffer ${ITK_LIBRARIES})

endif( "${ITK_VERSION_MAJOR}" LESS 4 )

</syntaxhighlight>

Download and Build ConvertPixelBuffer

Click here to download ConvertPixelBuffer and its CMakeLists.txt file. Once the tarball ConvertPixelBuffer.tar has been downloaded and extracted,

cd ConvertPixelBuffer/build

• If ITK is installed:

cmake ..

• If ITK is not installed but compiled on your system, you will need to specify the path to your ITK build:

cmake -DITK_DIR:PATH=/home/me/itk_build ..

Build the project:

make

and run it:

./ConvertPixelBuffer

WINDOWS USERS PLEASE NOTE: Be sure to add the ITK bin directory to your path. This will resolve the ITK dll's at run time.

Building All of the Examples

Many of the examples in the ITK Wiki Examples Collection require VTK. You can build all of the the examples by following these instructions. If you are a new VTK user, you may want to try the Superbuild which will build a proper ITK and VTK.

ItkVtkGlue

ITK >= 4

For examples that use QuickView (which depends on VTK), you must have built ITK with Module_ITKVtkGlue=ON.

ITK < 4

Some of the ITK Examples require VTK to display the images. If you download the entire ITK Wiki Examples Collection, the ItkVtkGlue directory will be included and configured. If you wish to just build a few examples, then you will need to download ItkVtkGlue and build it. When you run cmake it will ask you to specify the location of the ItkVtkGlue binary directory.