Hello, World

A simple program to write a simple .exr file of an image of 10x10 pixels with values that are a ramp in green and blue:

#include <ImfRgbaFile.h>
#include <ImfArray.h>
#include <iostream>

int
main()
{
    int width =  10;
    int height = 10;
        
    Imf::Array2D<Imf::Rgba> pixels(width, height);
    for (int y=0; y<height; y++)
        for (int x=0; x<width; x++)
            pixels[y][x] = Imf::Rgba(0, x / (width-1.0f), y / (height-1.0f));
        
    try {
        Imf::RgbaOutputFile file ("hello.exr", width, height, Imf::WRITE_RGBA);
        file.setFrameBuffer (&pixels[0][0], 1, width);
        file.writePixels (height);
    } catch (const std::exception &e) {
        std::cerr << "error writing image file hello.exr:" << e.what() << std::endl;
        return 1;
    }
    return 0;
}

And the CMakeLists.txt file to build:

cmake_minimum_required(VERSION 3.12)
project(exrwriter)
find_package(OpenEXR REQUIRED)

add_executable(${PROJECT_NAME} writer.cpp)
target_link_libraries(${PROJECT_NAME} OpenEXR::OpenEXR)

To build:

$ mkdir _build
$ cmake -S . -B _build
$ cmake --build _build

For more details, see The OpenEXR API.

And a simple program to read an .exr file:

#include <ImfRgbaFile.h>
#include <ImfArray.h>
#include <iostream>

int
main()
{
    try {
        Imf::RgbaInputFile file("hello.exr");
        Imath::Box2i       dw = file.dataWindow();
        int                width  = dw.max.x - dw.min.x + 1;
        int                height = dw.max.y - dw.min.y + 1;

        Imf::Array2D<Imf::Rgba> pixels(width, height);
        
        file.setFrameBuffer(&pixels[0][0], 1, width);
        file.readPixels(dw.min.y, dw.max.y);

    } catch (const std::exception &e) {
        std::cerr << "error reading image file hello.exr:" << e.what() << std::endl;
        return 1;
    }

    return 0;
}

And the CMakeLists.txt file to build:

cmake_minimum_required(VERSION 3.12)
project(exrreader)
find_package(OpenEXR REQUIRED)

add_executable(${PROJECT_NAME} reader.cpp)
target_link_libraries(${PROJECT_NAME} OpenEXR::OpenEXR)

To build:

$ mkdir _build
$ cmake -S . -B _build
$ cmake --build _build