vtk-m/docs/changelog/image_io.md

Implemented PNG/PPM image Readers/Writers

The original implementation of writing image data was only performed as a proxy through the Canvas rendering class. In order to implement true support for image-based regression testing, this interface needed to be expanded upon to support reading/writing arbitrary image data and storing it in a vtkm::DataSet. Using the new vtkm::io::PNGReader and vtkm::io::PPMReader it is possible to read data from files and Cavases directly and store them as a point field in a 2D uniform vtkm::DataSet

auto reader = vtkm::io::PNGReader();
auto imageDataSet = reader.ReadFromFile("read_image.png");

Similarly, the new vtkm::io::PNGWriter and vtkm::io::PPMWriter make it possible to write out a 2D uniform vtkm::DataSet directly to a file.

auto writer = vtkm::io::PNGWriter();
writer.WriteToFile("write_image.png", imageDataSet);

If canvas data is to be written out, the reader provides a method for converting a canvas's data to a vtkm::DataSet.

auto reader = vtkm::io::PNGReader();
auto dataSet = reader.CreateImageDataSet(canvas);
auto writer = vtkm::io::PNGWriter();
writer.WriteToFile("output.png", dataSet);