About

This repo contains the source code and results in the ICCV 2023 paper Computationally-Efficient Neural Image Compression with Shallow Decoders (formerly titled "Asymmetrically-powered Neural Image Compression with Shallow Decoders").

The high-level idea is to improve the decoding efficiency of neural compression (see intro article) by adopting an asymmetric autoencoder architecture, which pairs a powerful encoder (and potentially one that is defined implicitly through iterative optimization) with a shallow/lightweight decoder. This results in competitive rate-distortion performance at a drastically reduced decoding computation budget.

As far as we know, this is the first neural image compression method to operate with a decoding budget of less than 50K FLOPs/pixel while achieving rate-distortion performance competitive with BPG, when measured in PSNR and BPP.

UPDATE [Nov 1, 2023] Added pretrained checkpoints; download them here. See notebooks/vis_syn_filters.ipynb for an example for how to load a model and visualize the learned filters of the synthesis transform.

Software

• The code was developed in a python 3.10 environment on Linux. The required packages are listed in requirements.txt. The main dependices are tensorflow 2.10 and tensorflow-compression 2.10, which can be installed by pip install tensorflow-compression==2.10.0 (we recommend doing so in a new conda environment).
• The code has been written to separate the training/evaluation/iterative inference logic from the model architecture, and makes it easy to run hyperparameter sweep with Slurm (optional, but recommended).
• At the highest level, model architectures are distinguished by the type of entropy model/prior they use. For a given choice of entropy model, one is free to plug in different kinds of transforms (collected in common/transforms.py) and experiment with different hyperparameters (defined in configs subdirectory of each model directory). The code currently supports the following entropy models:
  • Factorized prior (Ballé et al. 2017): ./factorized
  • Mean-scale hyperprior (Minnen et al. 2018): ./mshyper
• There is some basic support for timing the transforms in graph mode, but can be inaccurate because of occasional JIT compilation slowdowns.

Setup

• Update the overall project configuration in configs.py according to your system and location of your data. You can find instructions for obtaining coco, kodak, and tecnick data in https://github.com/mandt-lab/RD-sandwich#data-preparation
• To use Slurm, create a directory called './slurm_jobs', and modify slurm_template.py to perform your own software setup (e.g., load cuda, activate conda environment, etc.).

Training

Here's an example command to train a factorized prior model, with default hyperparameter settings defined in a config file (run from the project root dir):

python -m factorized.train --config factorized/configs/bls2017.py --alsologtostderr

Here's another example for training the two-layer synthesis + ELIC analysis model:

python -m mshyper.train --config mshyper/configs/two_layer_syn.py --alsologtostderr

Here's an example command to launch Slurm training jobs with a hyperparameter sweep defined in the config file:

./launch.py --main mshyper.train --config mshyper/configs/two_layer_syn.py

By default, the experiment output will be written to project_dir/train_xms. Each experiment is identified by a unique id ("xid"; this is a string of number assigned by Slurm or a timestamp when not running with Slurm); within each experiment there can be multiple runs, each run on a different work unit with its own integer id ("wid"; this is simply the integer index of the hyperparameter setting being used in the hyperparameter sweep (defined by get_hyper in the config file)). The output of each work unit will be stored in project_dir/train_xms/xid/run_dir, where run_dir consists of a work unit id (like "wid=2") and a "runname" automatically generated from the hyperparameter setting (e.g., "num_filters=256-lr=0.001").

The logs and intermediate reconstructions can be viewed on tensorboard (just run the usual tensorboard --logdir your_workdir command).

Below is a list of model architectures from the paper and the corresponding "config" files for training experiments:

Model	Config file
Ballé et al. 2017	factorized/configs/bls2017.py
Minnen et al. 2018 (mean-scale Hyperprior)	mshyper/configs/mbt2018.py
Proposed JPEG-like (one-layer) synthesis + ELIC analysis	mshyper/configs/jpegl.py
Proposed two-layer synthesis + ELIC analysis	mshyper/configs/two_layer_syn.py
No-residual two-layer synthesis + CNN analysis + mixed quantization training*	mshyper/configs/two_layer_syn2.py

*In additional experiments we found this combination to give further improved R-D performance than the proposed two-layer synthesis + ELIC analysis.

Some pretrained checkpoints can be found here. See an example of working with a checkpoint here.

Evaluation

Here's an example command to launch Slurm jobs for evaluating trained checkpoints, on a dataset called $dataset_name:

./launch_eval.py --workdirs 'train_xms/188188/wid=*' --dataset $dataset_name

where train_xms/188188/wid=* is an example glob pattern that matches the workdirs of the runs to be evaluated. The results will be written to json_results/$dataset_name/end_to_end. Additional flags for eval.py can be passed to launch_eval.py via --args (e.g., controlling where results are stored and whether to skip eval when there are existing result files).

Iterative Inference

Here's an example command to launch Slurm jobs running iterative inference on pretrained checkpoints that use the hyperprior entropy model (substitute factorized for mshyper for models that use the factorized prior):

./launch.py --main mshyper.itinf --config mshyper/configs/itinf.py

This is basically the same as the train command; see details in the mshyper/configs/itinf.py config file.

The results will be stored in project_dir/itinf_xms/, with a similar naming convention/organization to the model training experiments.

You can find a demo of SGA here.