This is a TensorFlow model for compressing and decompressing images using an already trained Residual GRU model as descibed in [Full Resolution Image Compression with Recurrent Neural Networks] (https://arxiv.org/abs/1608.05148). Please consult the paper for more details on the architecture and compression results.
This code will allow you to perform the lossy compression on an model already trained on compression. This code doesn't not currently contain the Entropy Coding portions of our paper.
The only software requirements for running the encoder and decoder is having Tensorflow installed. You will also need to [download] (http://download.tensorflow.org/models/compression_residual_gru-2016-08-23.tar.gz) and extract the model residual_gru.pb.
If you want to generate the perceptual similarity under MS-SSIM, you will also need to Install SciPy.
The Residual GRU network is fully convolutional, but requires the images height and width in pixels by a multiple of 32. There is an image in this folder called example.png that is 768x1024 if one is needed for testing. We also rely on TensorFlow's built in decoding ops, which support only PNG and JPEG at time of release.
To encode an image, simply run the following command:
python encoder.py --input_image=/your/image/here.png --output_codes=output_codes.npz --iteration=15 --model=/path/to/model/residual_gru.pb
The iteration parameter specifies the lossy-quality to target for compression. The quality can be [0-15], where 0 corresponds to a target of 1/8 (bits per pixel) bpp and every increment results in an additional 1/8 bpp.
| Iteration | BPP | Compression Ratio |
|---|---|---|
| 0 | 0.125 | 192:1 |
| 1 | 0.250 | 96:1 |
| 2 | 0.375 | 64:1 |
| 3 | 0.500 | 48:1 |
| 4 | 0.625 | 38.4:1 |
| 5 | 0.750 | 32:1 |
| 6 | 0.875 | 27.4:1 |
| 7 | 1.000 | 24:1 |
| 8 | 1.125 | 21.3:1 |
| 9 | 1.250 | 19.2:1 |
| 10 | 1.375 | 17.4:1 |
| 11 | 1.500 | 16:1 |
| 12 | 1.625 | 14.7:1 |
| 13 | 1.750 | 13.7:1 |
| 14 | 1.875 | 12.8:1 |
| 15 | 2.000 | 12:1 |
The output_codes file contains the numpy shape and a flattened, bit-packed array of the codes. These can be inspected in python by using numpy.load().
After generating codes for an image, the lossy reconstructions for that image can be done as follows:
python decoder.py --input_codes=codes.npz --output_directory=/tmp/decoded/ --model=residual_gru.pb
The output_directory will contain images decoded at each quality level.
One of our primary metrics for comparing how similar two images are is MS-SSIM.
To generate these metrics on your images you can run:
python msssim.py --original_image=/path/to/your/image.png --compared_image=/tmp/decoded/image_15.png
We currently don't provide the code to build and train a compression graph from scratch.
This is usually due to the fact that our network only supports images that are both height and width divisible by 32 pixel. Try padding your images to 32 pixel boundaries.
Model repository maintained by Nick Johnston (nickj-google).