eSSIM[1] is an evolution of SSIM which improves correlation with subjective scores by employing Coefficient of Variation (CoV) pooling and reduces complexity by employing box filters and striding.

This is similar to the original algorithm implemented at https://github.com/utlive/enhanced_ssim but this project is designed for use at scale and uses optimized floating point and integer SIMD instructions.

In addition to the CoV pooled eSSIM score this library will also calculate the arithmetic mean pooled SSIM score. While CoV pooling has better correlation to subjective scores, and works well in practice for evaluating typical compression and scaling artifacts, it can exhibit unstable behaviors for adversarially generated image pairs. Therefore, mean pooled SSIM may be needed as a fallback when evaluated images with unknown distortion types.

[1] A. K. Venkataramanan, C. Wu, A. C. Bovik, I. Katsavounidis and Z. Shahid, "A Hitchhiker’s Guide to Structural Similarity," in IEEE Access, vol. 9, pp. 28872-28896, 2021, doi: 10.1109/ACCESS.2021.3056504 https://ieeexplore.ieee.org/document/9344648

This project uses CMake to build and depends on clang-tidy and clang-format for linting and auto formatting of source files. You can install both by installing llvm. On OS X you can use homebrew, but it won't link llvm so you need to manualy symlink the related binaries.

brew install llvm
sudo ln -s "$(brew --prefix llvm)/bin/clang-tidy" "/usr/local/bin/clang-tidy"
sudo ln -s "$(brew --prefix llvm)/bin/clang-tidy" "/usr/local/bin/clang-format"
sudo ln -s "$(brew --prefix llvm)/bin/clang-apply-replacements" "/usr/local/bin/clang-apply-replacements"\n

To build the project, use the following

mkdir build
cd build
cmake ..
make

CMake will download and install GoogleTest. To skip building tests you can uses

cmake .. -DBUILD_TESTS=OFF

Assuming you didn't skip building tests you can run tests using ctest

ctest --output-on-failure

To build x86 code instead of ARM on MacOS machines with M1 or later ARM CPUs you can use the CMAKE_OSX_ARCHITECTURES flag

cmake .. -DCMAKE_OSX_ARCHITECTURES=x86_64

First build the project. While building the project, don't skip building tests.

Copy "essim-staging/yuvtestsuite/gtest_main.cc" file to "build/_deps/googletest-src/googletest/src/"

In below mentioned file add "essim" folder path in "gtest_build_include_dirs". "build/_deps/googletest-src/googletest/CMakeLists.txt".

Example is shown here :

set(gtest_build_include_dirs "${gtest_SOURCE_DIR}/../../../../essim" "${gtest_SOURCE_DIR}/include" "${gtest_SOURCE_DIR}")

To get eSSIM score for ref & dist YUV files, enable "FR_LVL_eSSIM_SUPPORT" macro which is present in "gtest_main.cc" file.

You can use ESSIM as an ffmpeg filter, using the included vf_essim.c filter definition in the ffmpeg folder, and the associated patch to ffmpeg to enable building support for essim.

ESSIM is licensed the BSD-3 license, see LICENSE file in the root of this source tree for details.

The ffmpeg filter vf_essim.c is licensed under the LGPG license, same as vf_ssim.c in FFmpeg itself, upon which it is based.