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:

_images/stripes.png

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