Subtract Constant From Every Pixel

Synopsis

Subtract a constant from every pixel in an image.

Results

output.png

Code

C++

#include "itkImage.h"
#include "itkSubtractImageFilter.h"
#include "itkImageFileWriter.h"

using ImageType = itk::Image<unsigned char, 2>;
static void
CreateImage(ImageType::Pointer image);

int
main(int, char *[])
{
  ImageType::Pointer image = ImageType::New();
  CreateImage(image);

  using SubtractImageFilterType = itk::SubtractImageFilter<ImageType, ImageType, ImageType>;
  SubtractImageFilterType::Pointer subtractConstantFromImageFilter = SubtractImageFilterType::New();
  subtractConstantFromImageFilter->SetInput(image);
  subtractConstantFromImageFilter->SetConstant2(2);
  subtractConstantFromImageFilter->Update();

  using WriterType = itk::ImageFileWriter<ImageType>;
  WriterType::Pointer writer = WriterType::New();
  writer->SetFileName("output.png");
  writer->SetInput(subtractConstantFromImageFilter->GetOutput());
  writer->Update();

  return EXIT_SUCCESS;
}

void
CreateImage(ImageType::Pointer image)
{
  ImageType::IndexType start;
  start.Fill(0);

  ImageType::SizeType size;
  size.Fill(100);

  ImageType::RegionType region;
  region.SetSize(size);
  region.SetIndex(start);

  image->SetRegions(region);
  image->Allocate();

  itk::ImageRegionIterator<ImageType> imageIterator(image, region);

  while (!imageIterator.IsAtEnd())
  {
    if (imageIterator.GetIndex()[0] < 70)
    {
      imageIterator.Set(255);
    }
    else
    {
      imageIterator.Set(0);
    }

    ++imageIterator;
  }
}

Classes demonstrated

template<typename TInputImage1, typename TInputImage2 = TInputImage1, typename TOutputImage = TInputImage1>
class SubtractImageFilter : public itk::BinaryGeneratorImageFilter<TInputImage1, TInputImage2, TOutputImage>

Pixel-wise subtraction of two images.

Subtract each pixel from image2 from its corresponding pixel in image1:

Output = Input1 - Input2.

This is done using

SetInput1( image1 );
SetInput2( image2 );

This class is templated over the types of the two input images and the type of the output image. Numeric conversions (castings) are done by the C++ defaults.

Additionally, a constant can be subtracted from every pixel in an image using:

SetInput1( image1 );
SetConstant2( constant );

Note

The result of AddImageFilter with a negative constant is not necessarily the same as SubtractImageFilter. This would be the case when the PixelType defines an operator-() that is not the inverse of operator+()

ITK Sphinx Examples:

• All ITK Sphinx Examples

• Subtract Two Images

• Subtract Constant From Every Pixel

See itk::SubtractImageFilter for additional documentation.