ITK  5.2.0
Insight Toolkit
Examples/Filtering/GradientMagnitudeImageFilter.cxx
/*=========================================================================
*
* Copyright NumFOCUS
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0.txt
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
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*=========================================================================*/
// Software Guide : BeginCommandLineArgs
// INPUTS: {BrainProtonDensitySlice.png}
// OUTPUTS: {GradientMagnitudeImageFilterOutput.png}
// Software Guide : EndCommandLineArgs
//
// Software Guide : BeginLatex
//
// The magnitude of the image gradient is extensively used in image analysis,
// mainly to help in the determination of object contours and the
// separation of homogeneous regions. The
// \doxygen{GradientMagnitudeImageFilter} computes the magnitude of the
// image gradient at each pixel location using a simple finite differences
// approach. For example, in the case of $2D$ the computation is equivalent
// to convolving the image with masks of type
//
// \begin{center}
// \begin{picture}(200,50)
// \put( 5.0,32.0){\framebox(30.0,15.0){-1}}
// \put(35.0,32.0){\framebox(30.0,15.0){0}}
// \put(65.0,32.0){\framebox(30.0,15.0){1}}
// \put(105.0,17.0){\framebox(20.0,15.0){1}}
// \put(105.0,32.0){\framebox(20.0,15.0){0}}
// \put(105.0,47.0){\framebox(20.0,15.0){-1}}
// \end{picture}
// \end{center}
//
// then adding the sum of their squares and computing the square root of the
// sum.
//
// This filter will work on images of any dimension thanks to the internal
// use of \doxygen{NeighborhoodIterator} and \doxygen{NeighborhoodOperator}.
//
// \index{itk::GradientMagnitudeImageFilter}
//
// Software Guide : EndLatex
#include "itkImage.h"
// Software Guide : BeginLatex
//
// The first step required to use this filter is to include its header file.
//
// \index{itk::GradientMagnitudeImageFilter!header}
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
// Software Guide : EndCodeSnippet
int
main(int argc, char * argv[])
{
if (argc < 3)
{
std::cerr << "Usage: " << std::endl;
std::cerr << argv[0] << " inputImageFile outputImageFile " << std::endl;
return EXIT_FAILURE;
}
// Software Guide : BeginLatex
//
// Types should be chosen for the pixels of the input and output images.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
using InputPixelType = float;
using OutputPixelType = float;
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// The input and output image types can be defined using the pixel types.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
using InputImageType = itk::Image<InputPixelType, 2>;
using OutputImageType = itk::Image<OutputPixelType, 2>;
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// The type of the gradient magnitude filter is defined by the
// input image and the output image types.
//
// \index{itk::GradientMagnitudeImageFilter!instantiation}
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
using FilterType =
// Software Guide : EndCodeSnippet
ReaderType::Pointer reader = ReaderType::New();
reader->SetFileName(argv[1]);
// Software Guide : BeginLatex
//
// A filter object is created by invoking the \code{New()} method and
// assigning the result to a \doxygen{SmartPointer}.
//
// \index{itk::GradientMagnitudeImageFilter!New()}
// \index{itk::GradientMagnitudeImageFilter!Pointer}
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
FilterType::Pointer filter = FilterType::New();
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// The input image can be obtained from the output of another filter. Here,
// the source is an image reader.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
filter->SetInput(reader->GetOutput());
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// Finally, the filter is executed by invoking the \code{Update()} method.
//
// \index{itk::GradientMagnitudeImageFilter!Update()}
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
filter->Update();
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// If the output of this filter has been connected to other filters in a
// pipeline, updating any of the downstream filters will also trigger an
// update of this filter. For example, the gradient magnitude filter may be
// connected to an image writer.
//
// Software Guide : EndLatex
using WritePixelType = unsigned char;
using WriteImageType = itk::Image<WritePixelType, 2>;
using RescaleFilterType =
RescaleFilterType::Pointer rescaler = RescaleFilterType::New();
rescaler->SetOutputMinimum(0);
rescaler->SetOutputMaximum(255);
WriterType::Pointer writer = WriterType::New();
writer->SetFileName(argv[2]);
// Software Guide : BeginCodeSnippet
rescaler->SetInput(filter->GetOutput());
writer->SetInput(rescaler->GetOutput());
writer->Update();
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// \begin{figure}
// \center
// \includegraphics[width=0.44\textwidth]{BrainProtonDensitySlice}
// \includegraphics[width=0.44\textwidth]{GradientMagnitudeImageFilterOutput}
// \itkcaption[GradientMagnitudeImageFilter output]{Effect of the
// GradientMagnitudeImageFilter on a slice from a MRI proton density image
// of the brain.}
// \label{fig:GradientMagnitudeImageFilterInputOutput}
// \end{figure}
//
// Figure \ref{fig:GradientMagnitudeImageFilterInputOutput} illustrates the
// effect of the gradient magnitude filter on a MRI proton density image of
// the brain. The figure shows the sensitivity of this filter to noisy
// data.
//
// Attention should be paid to the image type chosen to represent the
// output image since the dynamic range of the gradient magnitude image is
// usually smaller than the dynamic range of the input image. As always,
// there are exceptions to this rule, for example, synthetic images that
// contain high contrast objects.
//
// This filter does not apply any smoothing to the image before computing
// the gradients. The results can therefore be very sensitive to noise and
// may not be the best choice for scale-space analysis.
//
// Software Guide : EndLatex
return EXIT_SUCCESS;
}
itk::GradientMagnitudeImageFilter
Computes the gradient magnitude of an image region at each pixel.
Definition: itkGradientMagnitudeImageFilter.h:42
itkImageFileReader.h
itkImage.h
itk::ImageFileReader
Data source that reads image data from a single file.
Definition: itkImageFileReader.h:75
itk::ImageFileWriter
Writes image data to a single file.
Definition: itkImageFileWriter.h:87
itkRescaleIntensityImageFilter.h
itkImageFileWriter.h
itk::RescaleIntensityImageFilter
Applies a linear transformation to the intensity levels of the input Image.
Definition: itkRescaleIntensityImageFilter.h:154
itk::Image
Templated n-dimensional image class.
Definition: itkImage.h:86
itkGradientMagnitudeImageFilter.h