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Pretrained Deep Neural Networks

You can take a pretrained image classification neural network that has already learned to extract powerful and informative features from natural images and use it as a starting point to learn a new task. The majority of the pretrained neural networks are trained on a subset of the ImageNet database [1], which is used in the ImageNet Large-Scale Visual Recognition Challenge (ILSVRC) [17]. These neural networks have been trained on more than a million images and can classify images into 1000 object categories, such as keyboard, coffee mug, pencil, and many animals. Using a pretrained neural network with transfer learning is typically much faster and easier than training a neural network from scratch.

You can use previously trained neural networks for the following tasks:

PurposeDescription
Classification

Apply pretrained neural networks directly to classification problems. To classify a new images, use minibatchpredict. To convert the predicted classification scores to labels, use the scores2label function. For an example showing how to use a pretrained neural network for classification, see Classify Image Using GoogLeNet.

Feature Extraction

Use a pretrained neural network as a feature extractor by using the layer activations as features. You can use these activations as features to train another machine learning model, such as a support vector machine (SVM). For more information, see Feature Extraction. For an example, see Extract Image Features Using Pretrained Network.

Transfer Learning

Take layers from a neural network trained on a large data set and fine-tune on a new data set. For more information, see Transfer Learning. For a simple example, see Get Started with Transfer Learning. To try more pretrained neural networks, see Retrain Neural Network to Classify New Images.

Compare Pretrained Neural Networks

Pretrained neural networks have different characteristics that matter when choosing a neural network to apply to your problem. The most important characteristics are neural network accuracy, speed, and size. Choosing a neural network is generally a tradeoff between these characteristics. Use the plot below to compare the ImageNet validation accuracy with the time required to make a prediction using the neural network.

Tip

To get started with transfer learning, try choosing one of the faster neural networks, such as SqueezeNet or GoogLeNet. You can then iterate quickly and try out different settings such as data preprocessing steps and training options. Once you have a feeling of which settings work well, try a more accurate neural network such as Inception-v3 or a ResNet and see if that improves your results.

Comparison of the accuracy and relative prediction time of the pretrained neural networks. As the accuracy of the pretrained neural networks increases, so does the relative prediction time.

Note

The plot above only shows an indication of the relative speeds of the different neural networks. The exact prediction and training iteration times depend on the hardware and mini-batch size that you use.

A good neural network has a high accuracy and is fast. The plot displays the classification accuracy versus the prediction time when using a modern GPU (an NVIDIA® Tesla® P100) and a mini-batch size of 128. The prediction time is measured relative to the fastest neural network. The area of each marker is proportional to the size of the neural network on disk.

The classification accuracy on the ImageNet validation set is the most common way to measure the accuracy of neural networks trained on ImageNet. Neural networks that are accurate on ImageNet are also often accurate when you apply them to other natural image data sets using transfer learning or feature extraction. This generalization is possible because the neural networks have learned to extract powerful and informative features from natural images that generalize to other similar data sets. However, high accuracy on ImageNet does not always transfer directly to other tasks, so it is a good idea to try multiple neural networks.

If you want to perform prediction using constrained hardware or distribute neural networks over the Internet, then also consider the size of the neural network on disk and in memory.

Neural Network Accuracy

There are multiple ways to calculate the classification accuracy on the ImageNet validation set and different sources use different methods. Sometimes an ensemble of multiple models is used and sometimes each image is evaluated multiple times using multiple crops. Sometimes the top-5 accuracy instead of the standard (top-1) accuracy is quoted. Because of these differences, it is often not possible to directly compare the accuracies from different sources. The accuracies of pretrained neural networks in Deep Learning Toolbox™ are standard (top-1) accuracies using a single model and single central image crop.

Load Pretrained Neural Networks

To load the SqueezeNet neural network, use the imagePretrainedNetwork function.

[net,classNames] = imagePretrainedNetwork;

For other neural networks, specify the model using the first argument of the imagePretrainedNetwork function. If you do not have the required support package for the network, the function provides a link to download it. Alternatively, you can download the pretrained neural networks from the Add-On Explorer.

This table lists the available pretrained neural networks trained on ImageNet and some of their properties. The neural network depth is defined as the largest number of sequential convolutional or fully connected layers on a path from the network input to the network output. The inputs to all neural networks are RGB images.

imagePretrainedNetwork Model Name ArgumentNeural Network NameDepthSizeParameters (Millions)Image Input SizeRequired Support Package
"squeezenet"SqueezeNet [2] 18

5.2 MB

1.24

227-by-227

None
"googlenet"GoogLeNet [3][4]22

27 MB

7.0

224-by-224

Deep Learning Toolbox Model for GoogLeNet Network

"googlenet-places365"
"inceptionv3"Inception-v3 [5]48

89 MB

23.9

299-by-299

Deep Learning Toolbox Model for Inception-v3 Network
"densenet201"DenseNet-201 [6]201

77 MB

20.0

224-by-224

Deep Learning Toolbox Model for DenseNet-201 Network
"mobilenetv2"MobileNet-v2 [7]53

13 MB

3.5

224-by-224

Deep Learning Toolbox Model for MobileNet-v2 Network
"resnet18"ResNet-18 [8]18

44 MB

11.7

224-by-224

Deep Learning Toolbox Model for ResNet-18 Network
"resnet50"ResNet-50 [8]50

96 MB

25.6

224-by-224

Deep Learning Toolbox Model for ResNet-50 Network
"resnet101"ResNet-101 [8]101

167 MB

44.6

224-by-224

Deep Learning Toolbox Model for ResNet-101 Network
"xception"Xception [9]71

85 MB

22.9299-by-299Deep Learning Toolbox Model for Xception Network
"inceptionresnetv2"Inception-ResNet-v2 [10]164

209 MB

55.9

299-by-299

Deep Learning Toolbox Model for Inception-ResNet-v2 Network
"shufflenet"ShuffleNet [11]505.4 MB1.4224-by-224Deep Learning Toolbox Model for ShuffleNet Network
"nasnetmobile"NASNet-Mobile [12]*20 MB 5.3224-by-224Deep Learning Toolbox Model for NASNet-Mobile Network
"nasnetlarge"NASNet-Large [12]*332 MB88.9331-by-331Deep Learning Toolbox Model for NASNet-Large Network
"darknet19"DarkNet-19 [13]1978 MB20.8256-by-256Deep Learning Toolbox Model for DarkNet-19 Network
"darknet53"DarkNet-53 [13]53155 MB41.6256-by-256Deep Learning Toolbox Model for DarkNet-53 Network
"efficientnetb0"EfficientNet-b0 [14]8220 MB5.3

224-by-224

Deep Learning Toolbox Model for EfficientNet-b0 Network
"alexnet"AlexNet [15]8

227 MB

61.0

227-by-227

Deep Learning Toolbox Model for AlexNet Network
"vgg16"VGG-16 [16]16

515 MB

138

224-by-224

Deep Learning Toolbox Model for VGG-16 Network
"vgg19"VGG-19 [16]19

535 MB

144

224-by-224

Deep Learning Toolbox Model for VGG-19 Network

*The NASNet-Mobile and NASNet-Large neural networks do not consist of a linear sequence of modules.

GoogLeNet Trained on Places365

The standard GoogLeNet neural network is trained on the ImageNet data set but you can also load a neural network trained on the Places365 data set [18] [4]. The neural network trained on Places365 classifies images into 365 different place categories, such as field, park, runway, and lobby. To load a pretrained GoogLeNet neural network trained on the Places365 data set, use imagePretrainedNetwork("googlenet-places365"). When you perform transfer learning for a new task, the most common approach is to use neural networks pretrained on ImageNet. If the new task is similar to classifying scenes, then using the neural network trained on Places365 can give higher accuracies.

For information about pretrained neural networks suitable for audio tasks, see Pretrained Neural Networks for Audio Applications.

Visualize Pretrained Neural Networks

You can load and visualize pretrained neural networks using Deep Network Designer.

[net,classNames] = imagePretrainedNetwork;
deepNetworkDesigner(net)

Deep Network Designer displaying a pretrained SqueezeNet neural network

To view and edit layer properties, select a layer. Click the help icon next to the layer name for information on the layer properties.

Cross channel normalization layer selected in Deep Network Designer. The PROPERTIES pane shows the properties of the layer.

Explore other pretrained neural networks in Deep Network Designer by clicking New.

Deep Network Designer start page showing available pretrained neural networks

If you need to download a neural network, pause on the desired neural network and click Install to open the Add-On Explorer.

Feature Extraction

Feature extraction is an easy and fast way to use the power of deep learning without investing time and effort into training a full neural network. Because it only requires a single pass over the training images, it is especially useful if you do not have a GPU. You extract learned image features using a pretrained neural network, and then use those features to train a classifier, such as a support vector machine using fitcsvm (Statistics and Machine Learning Toolbox).

Try feature extraction when your new data set is very small. Since you only train a simple classifier on the extracted features, training is fast. It is also unlikely that fine-tuning deeper layers of the neural network improves the accuracy since there is little data to learn from.

  • If your data is very similar to the original data, then the more specific features extracted deeper in the neural network are likely to be useful for the new task.

  • If your data is very different from the original data, then the features extracted deeper in the neural network might be less useful for your task. Try training the final classifier on more general features extracted from an earlier neural network layer. If the new data set is large, then you can also try training a neural network from scratch.

ResNet neural networks are often good feature extractors. For an example showing how to use a pretrained neural network for feature extraction, see Extract Image Features Using Pretrained Network.

Transfer Learning

You can fine-tune deeper layers in the neural network by training the neural network on your new data set with the pretrained neural network as a starting point. Fine-tuning a neural network with transfer learning is often faster and easier than constructing and training a new neural network. The neural network has already learned a rich set of image features, but when you fine-tune the neural network it can learn features specific to your new data set. If you have a very large data set, then transfer learning might not be faster than training from scratch.

Tip

Fine-tuning a neural network often gives the highest accuracy. For very small data sets (fewer than about 20 images per class), try feature extraction instead.

Fine-tuning a neural network is slower and requires more effort than simple feature extraction, but since the neural network can learn to extract a different set of features, the final neural network is often more accurate. Fine-tuning usually works better than feature extraction as long as the new data set is not very small, because then the neural network has data to learn new features from. For examples showing how to perform transfer learning, see Prepare Network for Transfer Learning Using Deep Network Designer and Retrain Neural Network to Classify New Images.

Transfer learning workflow

Import and Export Neural Networks

You can import neural networks from TensorFlow™ 2, TensorFlow-Keras, PyTorch®, and the ONNX™ (Open Neural Network Exchange) model format. You can also export Deep Learning Toolbox neural networks to TensorFlow 2 and the ONNX model format.

Import Functions

External Deep Learning Platform and Model FormatImport Model as dlnetwork
TensorFlow neural network or TensorFlow-Keras neural network in SavedModel formatimportNetworkFromTensorFlow
Traced PyTorch model in a .pt fileimportNetworkFromPyTorch
Neural network in ONNX model formatimportNetworkFromONNX

The importNetworkFromTensorFlow, importNetworkFromPyTorch, and importNetworkFromONNX functions create automatically generated custom layers when you import a model with TensorFlow layers, PyTorch layers, or ONNX operators that the functions cannot convert to built-in MATLAB® layers. The functions save the automatically generated custom layers to a package in the current folder. For more information, see Autogenerated Custom Layers.

Export Functions

External Deep Learning Platform and Model FormatExport Neural Network or Layer Graph
TensorFlow 2 model in Python® packageexportNetworkToTensorFlow
ONNX model formatexportONNXNetwork

The exportNetworkToTensorFlow function saves a Deep Learning Toolbox neural network as a TensorFlow model in a Python package. For more information on how to load the exported model and save it in a standard TensorFlow format, see Load Exported TensorFlow Model and Save Exported TensorFlow Model in Standard Format.

By using ONNX as an intermediate format, you can interoperate with other deep learning frameworks that support ONNX model export or import.

Import neural networks from and export neural networks to external deep learning platforms.

Pretrained Neural Networks for Audio Applications

Audio Toolbox™ provides MATLAB and Simulink® support for pretrained audio deep learning networks. Use pretrained networks to classify sounds with YAMNet, estimate pitch with CREPE, extract feature embeddings with VGGish or OpenL3, and perform voice activity detection (VAD) with VADNet. You can also import and visualize audio pretrained neural networks using Deep Network Designer.

Use the audioPretrainedNetwork (Audio Toolbox) function to load a pretrained audio network. You can also use one of the end-to-end functions that handle the preprocessing the audio, network inference, and postprocessing the network output. This table lists the available pretrained audio neural networks.

audioPretrainedNetwork Model Name ArgumentNeural Network NamePreprocessing and Postprocessing FunctionsEnd-to-End FunctionSimulink Blocks
"yamnet"YAMNetyamnetPreprocess (Audio Toolbox)classifySound (Audio Toolbox)YAMNet (Audio Toolbox), Sound Classifier (Audio Toolbox)
"vggish"VGGishvggishPreprocess (Audio Toolbox)vggishEmbeddings (Audio Toolbox)VGGish (Audio Toolbox), VGGish Embeddings (Audio Toolbox)
"openl3"OpenL3openl3Preprocess (Audio Toolbox)openl3Embeddings (Audio Toolbox)OpenL3 (Audio Toolbox), OpenL3 Embeddings (Audio Toolbox)
"crepe"CREPEcrepePreprocess (Audio Toolbox), crepePostprocess (Audio Toolbox)pitchnn (Audio Toolbox)CREPE (Audio Toolbox), Deep Pitch Estimator (Audio Toolbox)
"vadnet"VADNetvadnetPreprocess (Audio Toolbox), vadnetPostprocess (Audio Toolbox)detectspeechnn (Audio Toolbox)None

For examples showing how to adapt pretrained audio neural networks for a new task, see Transfer Learning with Pretrained Audio Networks (Audio Toolbox) and Adapt Pretrained Audio Network for New Data Using Deep Network Designer.

For more information on using deep learning for audio applications, see Deep Learning for Audio Applications (Audio Toolbox).

Pretrained Models on GitHub

To find the latest pretrained models, see MATLAB Deep Learning Model Hub.

For example:

References

[1] ImageNet. http://www.image-net.org.

[2] Iandola, Forrest N., Song Han, Matthew W. Moskewicz, Khalid Ashraf, William J. Dally, and Kurt Keutzer. "SqueezeNet: AlexNet-level accuracy with 50x fewer parameters and <0.5 MB model size." Preprint, submitted November 4, 2016. https://arxiv.org/abs/1602.07360.

[3] Szegedy, Christian, Wei Liu, Yangqing Jia, Pierre Sermanet, Scott Reed, Dragomir Anguelov, Dumitru Erhan, Vincent Vanhoucke, and Andrew Rabinovich. "Going deeper with convolutions." In Proceedings of the IEEE conference on computer vision and pattern recognition, pp. 1-9. 2015.

[4] Places. http://places2.csail.mit.edu/

[5] Szegedy, Christian, Vincent Vanhoucke, Sergey Ioffe, Jon Shlens, and Zbigniew Wojna. "Rethinking the inception architecture for computer vision." In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition, pp. 2818-2826. 2016.

[6] Huang, Gao, Zhuang Liu, Laurens Van Der Maaten, and Kilian Q. Weinberger. "Densely Connected Convolutional Networks." In CVPR, vol. 1, no. 2, p. 3. 2017.

[7] Sandler, M., Howard, A., Zhu, M., Zhmoginov, A. and Chen, L.C. "MobileNetV2: Inverted Residuals and Linear Bottlenecks." In 2018 IEEE/CVF Conference on Computer Vision and Pattern Recognition (pp. 4510-4520). IEEE.

[8] He, Kaiming, Xiangyu Zhang, Shaoqing Ren, and Jian Sun. "Deep residual learning for image recognition." In Proceedings of the IEEE conference on computer vision and pattern recognition, pp. 770-778. 2016.

[9] Chollet, F., 2017. "Xception: Deep Learning with Depthwise Separable Convolutions." arXiv preprint, pp.1610-02357.

[10] Szegedy, Christian, Sergey Ioffe, Vincent Vanhoucke, and Alexander A. Alemi. "Inception-v4, Inception-ResNet and the Impact of Residual Connections on Learning." In AAAI, vol. 4, p. 12. 2017.

[11] Zhang, Xiangyu, Xinyu Zhou, Mengxiao Lin, and Jian Sun. "ShuffleNet: An Extremely Efficient Convolutional Neural Network for Mobile Devices." arXiv preprint arXiv:1707.01083v2 (2017).

[12] Zoph, Barret, Vijay Vasudevan, Jonathon Shlens, and Quoc V. Le. "Learning Transferable Architectures for Scalable Image Recognition." arXiv preprint arXiv:1707.07012 2, no. 6 (2017).

[13] Redmon, Joseph. “Darknet: Open Source Neural Networks in C.” https://pjreddie.com/darknet.

[14] Mingxing Tan and Quoc V. Le, “EfficientNet: Rethinking Model Scaling for Convolutional Neural Networks,” ArXiv Preprint ArXiv:1905.1194, 2019.

[15] Krizhevsky, Alex, Ilya Sutskever, and Geoffrey E. Hinton. "ImageNet Classification with Deep Convolutional Neural Networks." Communications of the ACM 60, no. 6 (May 24, 2017): 84–90. https://doi.org/10.1145/3065386

[16] Simonyan, Karen, and Andrew Zisserman. "Very deep convolutional networks for large-scale image recognition." arXiv preprint arXiv:1409.1556 (2014).

[17] Russakovsky, O., Deng, J., Su, H., et al. “ImageNet Large Scale Visual Recognition Challenge.” International Journal of Computer Vision (IJCV). Vol 115, Issue 3, 2015, pp. 211–252

[18] Zhou, Bolei, Aditya Khosla, Agata Lapedriza, Antonio Torralba, and Aude Oliva. "Places: An image database for deep scene understanding." arXiv preprint arXiv:1610.02055 (2016).

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