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)
-
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 ./
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 Benchmark
To build benchmarks, pass -DUHDR_BUILD_BENCHMARK=1 to cmake configure command and build.
This will additionally generate,
ultrahdr_bm
Benchmark tests
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:
List of encode APIs:
Input | HDR YUV | SDR YUV | JPEG | Encoded gainmap | Quality (0 ~ 100) | EXIF | Use case |
---|---|---|---|---|---|---|---|
API-0 | P010 | No | No | No | Required | Optional | Experimental only. |
API-1 | P010 | YUV_420 | No | No | Required | Optional | Raw SDR input. Primary image will be encoded from the raw SDR input in the library. |
API-2 | P010 | YUV_420 | Yes | No | No | No | Both JPEG and raw SDR inputs. Gainmap will be calculated from raw HDR and raw SDR inputs, the JPEG input will be preserved (including metadata) as the primary image. |
API-3 | P010 | No | Yes | No | No | No | SDR JPEG input. Gainmap will be calculated from raw HDR and the decoding result of the JPEG input, the JPEG input will be preserved (including metadata) as the primary image. |
API-4 | No | No | Yes | Yes | No | No | SDR JPEG and gainmap inputs. The library will only generate the Ultra HDR related metadata and write everything into the Ultra HDR format, all other metadata from the JPEG input will be preserved. |
List of decode API:
Input | Usage | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
compressed_jpegr_image | The input data. Pointer to JPEG/R stream. | ||||||||||
dest | The output data. Destination that decoded data to be written. | ||||||||||
max_display_boost | (optional, >= 1.0) the maximum available boost supported by a display. | ||||||||||
exif | (optional, default to NULL) Destination that exif data to be written. | ||||||||||
gain_map | (optional, default to NULL) Destination that decoded gain map data to be written. | ||||||||||
output_format |
|
||||||||||
metadata | (optional, default to NULL) Destination of metadata (gain map version, min/max content boost). |
For more info:
- Refer to jpegr.h for detailed description of various encode and decode api.
- Refer to ultrahdr_app.cpp for examples of its usage.