phunm211 / libultrahdr

Ultra HDR is a true 10-bit HDR image format, and is backcompatible. libultrahdr is the reference codec for the Ultra HDR format. The codecs that support the format can render the HDR intent of the image on HDR displays; other codecs can still decode and display the SDR intent of the image.

Background

libultrahdr is an image compression library that uses gain map technology to store and distribute HDR images. Conceptually on the encoding side, the library accepts SDR and HDR rendition of an image and from these a Gain Map (quotient between the two renditions) is computed. The library then uses backward compatible means to store the base image (SDR), gain map image and some associated metadata. Legacy readers that do not support parsing the gain map image and/or metadata, will display the base image. Readers that support the format combine the base image with the gain map and render a high dynamic range image on compatible displays.

More information about libultrahdr can be found at https://developer.android.com/guide/topics/media/platform/hdr-image-format.

Building libultrahdr

libultrahdr compresses base image and gain map image in to jpeg format. For this libjpeg-turbo is used. This is cloned from https://github.com/libjpeg-turbo/libjpeg-turbo.git and included in the build process.

Requirements

• CMake v3.13 or later

• NASM or Yasm (If libjpeg-turbo needs to be built with SIMD extensions)

  • If using NASM, 2.13 or later is required.
  • If using Yasm, 1.2.0 or later is required.
  • If building on macOS, NASM or Yasm can be obtained from MacPorts or Homebrew.

• Compilers with support for C++17

Should work with GCC v7 (or later) and Clang 5 (or later) on Linux and Mac Platforms.

Should work with Microsoft Visual C++ 2019 (or later) on Windows Platforms.

Build Procedure

To build libultrahdr, examples, unit tests:

Un*x (including Linux, Mac)

mkdir {build_directory}
cd {build_directory}
cmake -G "Unix Makefiles"  -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DUHDR_BUILD_TESTS=1 ../
make
ctest

This will generate the following files under {build_directory}:

libultrahdr.a
Static link library for the ultrahdr API

ultrahdr_app
Sample application demonstrating ultrahdr API

ultrahdr_unit_test
Unit tests

Visual C++ (IDE)

mkdir {build_directory}
cd {build_directory}
cmake -G "Visual Studio 16 2019" -DUHDR_BUILD_TESTS=1 ../
cmake --build ./ --config=Release
ctest -C Release

This will generate the following files under {build_directory/Release}:

ultrahdr.lib
Static link library for the ultrahdr API

ultrahdr_app.exe
Sample application demonstrating ultrahdr API

ultrahdr_unit_test.exe
Unit tests

Visual C++ (Command line)

mkdir {build_directory}
cd {build_directory}
cmake -G "NMake Makefiles" -DUHDR_BUILD_TESTS=1 ../
cmake --build ./ --config=Release
ctest

This will generate the following files under {build_directory}:

ultrahdr.lib
Static link library for the ultrahdr API

ultrahdr_app.exe
Sample application demonstrating ultrahdr API

ultrahdr_unit_test.exe
Unit tests

MinGW

NOTE: This assumes that you are building on a Windows machine using the MSYS environment.

mkdir {build_directory}
cd {build_directory}
cmake -G "MSYS Makefiles" -DUHDR_BUILD_TESTS=1 ../
cmake --build ./
ctest

mkdir {build_directory}
cd {build_directory}
cmake -G "MinGW Makefiles" -DUHDR_BUILD_TESTS=1 ../
cmake --build ./
ctest

This will generate the following files under {build_directory}:

libultrahdr.a
Static link library for the ultrahdr API

ultrahdr_app.exe
Sample application demonstrating ultrahdr API

ultrahdr_unit_test.exe
Unit tests

NOTE: To not build unit tests, skip passing -DUHDR_BUILD_TESTS=1

Building Fuzzers

Refer to README.md for complete instructions.

Using libultrahdr

libultrahdr includes two classes of APIs, one to compress and the other to decompress HDR images:

• Refer to jpegr.h for detailed description of various encode and decode api.
• Refer to ultrahdr_app.cpp for examples of its usage.