Hello, World

Write an Image

This example exrwriter.cpp program writes a simple image stripes.exr:

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

using namespace OPENEXR_IMF_NAMESPACE;

int
main()
{
    int width =  100;
    int height = 50;
        
    Array2D<Rgba> pixels(height, width);
    for (int y=0; y<height; y++)
    {
        float c = (y / 5 % 2 == 0) ? (y / (float) height) : 0.0;
        for (int x=0; x<width; x++)
            pixels[y][x] = Rgba(c, c, c);
    }

    try {
        RgbaOutputFile file ("stripes.exr", width, height, WRITE_RGBA);
        file.setFrameBuffer (&pixels[0][0], 1, width);
        file.writePixels (height);
    } catch (const std::exception &e) {
        std::cerr << "error writing image file stripes.exr:" << e.what() << std::endl;
        return 1;
    }
    return 0;
}

This creates an image 100 pixels wide and 50 pixels high with horizontal stripes 5 pixels high of graduated intensity, bright on the bottom of the image and dark towards the top. Note that pixel[0][0] is in the upper left:

The CMakeLists.txt file to build is:

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

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

To build:

$ mkdir _build
$ cmake -S . -B _build -DCMAKE_PREFIX_PATH=<path to OpenEXR libraries/includes>
$ cmake --build _build

For more details, see The OpenEXR API.

Read an Image

This companion example exrreader.cpp program reads the stripes.exr file written by the writer program above:

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

int
main()
{
    try {
        Imf::RgbaInputFile file("stripes.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 stripes.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(${PROJECT_NAME} exrreader.cpp)
target_link_libraries(${PROJECT_NAME} OpenEXR::OpenEXR)

To build:

$ mkdir _build
$ cmake -S . -B _build -DCMAKE_PREFIX_PATH=<path to OpenEXR libraries/includes>
$ cmake --build _build