Convert RGB Image to Grayscale Image

Synopsis

Convert a RGB Image to its luminance image (grayscale one).

Results

Input image

Output image

Code

Python

#!/usr/bin/env python

import itk
import argparse

parser = argparse.ArgumentParser(description="Compute RBG Image To Grayscale Image.")
parser.add_argument("input_image")
parser.add_argument("output_image")
args = parser.parse_args()

Dimension = 2

ComponentType = itk.UC
InputPixelType = itk.RGBPixel[ComponentType]
InputImageType = itk.Image[InputPixelType, Dimension]

OutputPixelType = itk.UC
OutputImageType = itk.Image[OutputPixelType, Dimension]

reader = itk.ImageFileReader[InputImageType].New()
reader.SetFileName(args.input_image)

rgbFilter = itk.RGBToLuminanceImageFilter.New(reader)

writer = itk.ImageFileWriter[OutputImageType].New()
writer.SetFileName(args.output_image)
writer.SetInput(rgbFilter.GetOutput())

writer.Update()

C++

#include "itkImage.h"
#include "itkImageFileReader.h"
#include "itkImageFileWriter.h"
#include "itkRGBToLuminanceImageFilter.h"

int
main(int argc, char * argv[])
{
  if (argc != 3)
  {
    std::cerr << "Usage: " << std::endl;
    std::cerr << argv[0];
    std::cerr << "<InputFileName> <OutputFileName>";
    std::cerr << std::endl;
    return EXIT_FAILURE;
  }

  constexpr unsigned int Dimension = 2;

  using ComponentType = unsigned char;
  using InputPixelType = itk::RGBPixel<ComponentType>;
  using InputImageType = itk::Image<InputPixelType, Dimension>;

  using ReaderType = itk::ImageFileReader<InputImageType>;
  ReaderType::Pointer reader = ReaderType::New();
  reader->SetFileName(argv[1]);

  using OutputPixelType = unsigned char;
  using OutputImageType = itk::Image<OutputPixelType, Dimension>;

  using FilterType = itk::RGBToLuminanceImageFilter<InputImageType, OutputImageType>;
  FilterType::Pointer filter = FilterType::New();
  filter->SetInput(reader->GetOutput());

  using WriterType = itk::ImageFileWriter<OutputImageType>;
  WriterType::Pointer writer = WriterType::New();
  writer->SetFileName(argv[2]);
  writer->SetInput(filter->GetOutput());

  try
  {
    writer->Update();
  }
  catch (itk::ExceptionObject & error)
  {
    std::cerr << "Error: " << error << std::endl;
    return EXIT_FAILURE;
  }

  return EXIT_SUCCESS;
}

Classes demonstrated

template<typename TInputImage, typename TOutputImage>
class RGBToLuminanceImageFilter : public itk::UnaryGeneratorImageFilter<TInputImage, TOutputImage>

Converts an RGB image into a grayscale image.

This filters converts an RGB image into a Luminance on by computing pixel-wise a linear combination on the Red, Green and Blue channels. The pixel type of the input image must have a GetLuminance() method. This is the case of the itk::RGBPixel class.

See itk::RGBToLuminanceImageFilter for additional documentation.