frugally-deep

Use Keras models in C++ with ease

Table of contents

• Introduction
• Usage
• Requirements and Installation
• FAQ

Introduction

Would you like to build/train a model using Keras/Python? And would you like to run the prediction (forward pass) on your model in C++ without linking your application against TensorFlow? Then frugally-deep is exactly for you.

frugally-deep

• is a small header-only library written in modern and pure C++.
• is very easy to integrate and use.
• depends only on FunctionalPlus, Eigen and json - also header-only libraries.
• supports inference (model.predict) not only for sequential models but also for computational graphs with a more complex topology, created with the functional API.
• re-implements a (small) subset of TensorFlow, i.e., the operations needed to support prediction.
• results in a much smaller binary size than linking against TensorFlow.
• works out-of-the-box also when compiled into a 32-bit executable. (Of course, 64 bit is fine too.)
• avoids temporarily allocating (potentially large chunks of) additional RAM during convolutions (by not materializing the im2col input matrix).
• utterly ignores even the most powerful GPU in your system and uses only one CPU core per prediction. ;-)
• but is quite fast on one CPU core, and you can run multiple predictions in parallel, thus utilizing as many CPUs as you like to improve the overall prediction throughput of your application/pipeline.

Supported layer types

• Add, Concatenate, Subtract, Multiply, Average, Maximum, Minimum, Dot
• AveragePooling1D/2D/3D, GlobalAveragePooling1D/2D/3D
• AdaptiveAveragePooling1D/2D/3D, AdaptiveMaxPooling1D/2D/3D
• TimeDistributed
• Conv1D/2D/3D, SeparableConv2D, DepthwiseConv1D, DepthwiseConv2D
• Conv1DTranspose, Conv2DTranspose, Conv3DTranspose
• Cropping1D/2D/3D, ZeroPadding1D/2D/3D, CenterCrop
• BatchNormalization, Dense, EinsumDense, Flatten, Normalization
• Dropout, AlphaDropout, GaussianDropout, GaussianNoise
• SpatialDropout1D, SpatialDropout2D, SpatialDropout3D
• ActivityRegularization, LayerNormalization, RMSNormalization
• GroupNormalization, UnitNormalization
• Training-only image augmentation layers (passed through at inference): RandomBrightness, RandomContrast, RandomCrop, RandomFlip, RandomHue, RandomGrayscale, RandomRotation, RandomTranslation, RandomZoom, RandomShear, RandomSaturation, RandomPerspective, AutoContrast, AugMix, CutMix, MixUp, RandAugment, Solarization, Equalization
• MaxPooling1D/2D/3D, GlobalMaxPooling1D/2D/3D
• UpSampling1D/2D/3D, Resizing, Rescaling
• Reshape, Permute, RepeatVector
• Embedding, CategoryEncoding
• Discretization, IntegerLookup
• Masking (passthrough at inference)
• Attention, AdditiveAttention, MultiHeadAttention, GroupedQueryAttention
• LSTM, GRU, SimpleRNN, Bidirectional
• RNN wrapping LSTMCell/GRUCell/SimpleRNNCell/StackedRNNCells
• ConvLSTM1D, ConvLSTM2D, ConvLSTM3D

Also supported

• different activiations (celu, elu, exponential, gelu, hard_shrink, hard_sigmoid, hard_tanh, leaky_relu, leakyrelu, linear, log_sigmoid, log_softmax, prelu, relu, relu6, selu, shared_activation, sigmoid, silu, soft_shrink, softmax, softplus, softsign, sparse_plus, squareplus, swish, tanh, tanh_shrink, threshold)
• multiple inputs and outputs
• nested models
• residual connections
• shared layers
• variable input shapes
• arbitrary complex model architectures / computational graphs
• custom layers (by passing custom factory functions to load_model)

Currently not supported are the following:

Lambda (why), Hashing, HashedCrossing, MelSpectrogram, STFTSpectrogram, StringLookup, TextVectorization, stateful recurrent layers, temporal models

Usage

1. Use Keras/Python to build (model.compile(...)), train (model.fit(...)) and test (model.evaluate(...)) your model as usual. Then save it to a single file using model.save('....keras'). The image_data_format in your model must be channels_last, which is the default when using the TensorFlow backend. Models created with a different image_data_format and other backends are not supported.

2. Now convert it to the frugally-deep file format with keras_export/convert_model.py

3. Finally load it in C++ (fdeep::load_model(...)) and use model.predict(...) to invoke a forward pass with your data.

The following minimal example shows the full workflow:

# create_model.py
import numpy as np
from keras.layers import Input, Dense
from keras.models import Model

inputs = Input(shape=(4,))
x = Dense(5, activation='relu')(inputs)
predictions = Dense(3, activation='softmax')(x)
model = Model(inputs=inputs, outputs=predictions)
model.compile(loss='categorical_crossentropy', optimizer='nadam')

model.fit(
    np.asarray([[1, 2, 3, 4], [2, 3, 4, 5]]),
    np.asarray([[1, 0, 0], [0, 0, 1]]), epochs=10)

model.save('keras_model.keras')

python3 keras_export/convert_model.py keras_model.keras fdeep_model.json

// main.cpp
#include <fdeep/fdeep.hpp>
int main()
{
    const auto model = fdeep::load_model("fdeep_model.json");
    const auto result = model.predict(
        {fdeep::tensor(fdeep::tensor_shape(static_cast<std::size_t>(4)),
        std::vector<float>{1, 2, 3, 4})});
    std::cout << fdeep::show_tensors(result) << std::endl;
}

When using convert_model.py a test case (input and corresponding output values) is generated automatically and saved along with your model. fdeep::load_model runs this test to make sure the results of a forward pass in frugally-deep are the same as in Keras.

For more integration examples please have a look at the FAQ.

Requirements and Installation

• A C++14-compatible compiler: Compilers from these versions on are fine: GCC 4.9, Clang 3.7 (libc++ 3.7) and Visual C++ 2015
• Python 3.9 or higher
• TensorFlow 2.21.0
• Keras 3.14.0

(These are the tested versions, but somewhat older ones might work too.)

Guides for different ways to install frugally-deep can be found in INSTALL.md.

FAQ

See FAQ.md

Disclaimer

The API of this library still might change in the future. If you have any suggestions, find errors, or want to give general feedback/criticism, I'd love to hear from you. Of course, contributions are also very welcome.

License

Distributed under the MIT License. (See accompanying file LICENSE or at https://opensource.org/licenses/MIT)