A Keras (branch tf2.2 supports TensorFlow 2) implementation of CapsNet in the paper:
Sara Sabour, Nicholas Frosst, Geoffrey E Hinton. Dynamic Routing Between Capsules. NIPS 2017
The current average test error = 0.34% and best test error = 0.30%.

Differences with the paper:

  • We use the learning rate decay with decay factor = 0.9 and step = 1 epoch, while the paper did not give the detailed parameters (or they didn't use it?).
  • We only report the test errors after 50 epochs training.
    In the paper, I suppose they trained for 1250 epochs according to Figure A.1? Sounds crazy, maybe I misunderstood.
  • We use MSE (mean squared error) as the reconstruction loss and the coefficient for the loss is lam_recon=0.0005*784=0.392. This should be equivalent with using SSE (sum squared error) and lam_recon=0.0005 as in the paper.


Please use Keras==2.0.7 with TensorFlow==1.2 backend, or the K.batch_dot function may not work correctly.

However, if you use Tensorflow>=2.0, then checkout branch tf2.2


Step 1. Clone this repository to local.

git clone capsnet-keras
cd capsnet-keras
git checkout tf2.2 # Only if use Tensorflow>=2.0

Step 2. Install Keras==2.0.7 with TensorFlow==1.2 backend.

pip install tensorflow-gpu==1.2
pip install keras==2.0.7

or install Tensorflow>=2.0

pip install tensorflow==2.2

Step 3. Train a CapsNet on MNIST

Training with default settings:


More detailed usage run for help:

python -h

Step 4. Test a pre-trained CapsNet model

Suppose you have trained a model using the above command, then the trained model will be saved to result/trained_model.h5. Now just launch the following command to get test results.

$ python -t -w result/trained_model.h5

It will output the testing accuracy and show the reconstructed images. The testing data is same as the validation data. It will be easy to test on new data, just change the code as you want.

You can also just download a model I trained from or

Step 5. Train on multi gpus

This requires Keras>=2.0.9. After updating Keras:

python --gpus 2

It will automatically train on multi gpus for 50 epochs and then output the performance on test dataset. But during training, no validation accuracy is reported.


Test Errors

CapsNet classification test error on MNIST. Average and standard deviation results are reported by 3 trials. The results can be reproduced by launching the following commands.

python --routings 1 --lam_recon 0.0    #CapsNet-v1   
python --routings 1 --lam_recon 0.392  #CapsNet-v2
python --routings 3 --lam_recon 0.0    #CapsNet-v3 
python --routings 3 --lam_recon 0.392  #CapsNet-v4
Method Routing Reconstruction MNIST (%) Paper
Baseline -- -- -- 0.39
CapsNet-v1 1 no 0.39 (0.024) 0.34 (0.032)
CapsNet-v2 1 yes 0.36 (0.009) 0.29 (0.011)
CapsNet-v3 3 no 0.40 (0.016) 0.35 (0.036)
CapsNet-v4 3 yes 0.34 (0.016) 0.25 (0.005)

Losses and accuracies:

Training Speed

About 100s / epoch on a single GTX 1070 GPU.
About 80s / epoch on a single GTX 1080Ti GPU.
About 55s / epoch on two GTX 1080Ti GPU by using

Reconstruction result

The result of CapsNet-v4 by launching

python -t -w result/trained_model.h5

Digits at top 5 rows are real images from MNIST and digits at bottom are corresponding reconstructed images.

Manipulate latent code

python -t --digit 5 -w result/trained_model.h5 

For each digit, the ith row corresponds to the ith dimension of the capsule, and columns from left to right correspond to adding [-0.25, -0.2, -0.15, -0.1, -0.05, 0, 0.05, 0.1, 0.15, 0.2, 0.25] to the value of one dimension of the capsule.

As we can see, each dimension has caught some characteristics of a digit. The same dimension of different digit capsules may represent different characteristics. This is because that different digits are reconstructed from different feature vectors (digit capsules). These vectors are mutually independent during reconstruction.

Other Implementations

Capsnet Keras

A Keras implementation of CapsNet in NIPS2017 paper "Dynamic Routing Between Capsules". Now test error = 0.34%.

Capsnet Keras Info

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