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How to use transfer learning to perform image classification on STM32
This article presents a video on how to use a technique called "Transfer learning" to quickly train a deep learning model in order to classify images.
This video teaches you how to use ST ecosystem to build a computer vision application from the ground up. It describes how the FP-AI-VISION1 allows easy image collection with an STM32 Discovery kit, how to use transfer learning with Tensorflow to quickly train an image classification model, and eventually how to use STM32Cube.AI to convert this model into optimized code for ST microcontrollers.
The Jupyter notebook used in this video is available on Github. It can be opened with Colab.
The article below describes step by step the video tutorial. For another complete example on how to use your own models with the FP-AI-VISION1 and Teachable Machine check out this article. In addition, this series of videos gives a good overview of the Vision function package.
1 Dataset generation
First you need a dataset of images representative of your classes. It can be generated either by following the steps described below or by using an already existing dataset (see related Github page for pasta datasets to jump start, note that it has been recorded with a fix distance of 13 cm and good light conditions). It is a good idea to use the same sensor for the dataset collection as the one that will be used for inference.
In the present example, the B-CAMS-OMV board is used as camera module.
Download the FP-AI-VISION1 function package from https://www.st.com/en/embedded-software/fp-ai-vision1.html.
Using the USB Webcam application provided within FP-AI-VISION1, the board and the camera can be used as a webcam.
First plug your board onto your computer using the ST-LINK port. Make sure the JP6 jumper is set to ST-LINK.
After plugging the USB cable onto your computer, the board appears as a mounted device.
The binary is located under
Drag and drop it onto the board mounted device. This flashes the binary on the board.
Unplug the board, change the JP6 jumper to the HS position, and plug your board using the USB OTG port.
Launch the Windows® camera application (it can be found by searching for “camera” in the Windows search bar). If your computer has already a camera, change the source of the image feed by clicking the “flip camera” button.
The capture can be done either in VGA or QVGA, the resolution can be changed with the menu
settings -> Photos -> Quality.
The images will be resized to the input resolution of the neural network in the Python notebook.
Take enough picture samples to fill your dataset. It must be structured as follows:
Dataset ├── cats │ ├── cat0001.jpg │ ├── cat0002.jpg │ └── ... ├── dogs └── horses
The dataset must to be large enough. The one used for the video includes 1408 files belonging to 8 classes. It is recommended to use at least 100 pictures per class.
2 Model generation
The Python notebook used to generate the model can be found at https://github.com/STMicroelectronics/stm32ai/blob/master/AI_resources/VISION/transfer_learning/TransferLearning.ipynb
It can be open either with Google Colab (as in the present example) or by using any Python environment.
Just click (or
Ctrl + Click) the
Open in Colab icon at the top of the notebook on Github. This takes you to the Colab notebook project.
Zip your dataset folder and import it to the Colab project.
You can run the script either step by step or run the whole script by pressing
Ctrl + F9.
All the steps are described in details in the script but what they do is straightforward :
- Import all the necessary libraries.
- Unzip the dataset.
- Import the dataset (this step also automatically resizes images to match the model input size).
- Display samples from the dataset
- Perform data augmentation by adding duplicate images with random contrast/translation/rotation/zoom.
- Display new samples.
- Normalize data.
- Import a pretrained
MobileNetmodel without the last layer and add new ones at the end.
- Train the model.
- Plot training loss history.
- Quantize the model to reduce its size.
- Export the quantized model.
The trained and quantized model appears as
3 Model deployment
This section describes how to generate a model that can be used on STM32 platforms, starting from a model produced by a high-level library such a Keras/Tensorlflow.
It also describes how to use your model in an already existing project.
3.1 Model generation for STM32
First convert the
tflite model to be used on a STM32 platform.
There are two ways to achieve this goal, one by using STM32CubeMX and generating an entire project (recommended at first), the other by using the command line interface to generate only the required files.
3.1.1 Project generation with STM32CubeMX (Option 1)
Start STM32CubeMX and create a new project. In this example, the STM32H747I-DISCO board is used. Select the board in the
Board Selector and start the project.
A new window opens showing the board configuration. Click
Software Packs -> Select Components.
Select the components for the Arm® Cortex®-M7 core under STMicroelectronics X-CUBE-AI, check the core box, select
Application as application, then click Ok.
The stm32-ai library will be download if it has not been downloaded yet. When it is complete, click Ok.
Software Packs (on the left) -> STMicroelectronics XCUBE AI. A pop up window opens to configure peripherals and clock.Click Yes.
Add network, call your network
network, select TFLite from the scrollable menu, and browse to the last section to find the generated model.
Once the model is selected, click
Analyze. This provides a quick overview of the model memory footprint. Click the
Show graph button for more in-depth information on the model topology and RAM memory usage layer by layer including activation buffers.
To customize how the model is stored in memory, click the gear icon (
Advanced Settings) and specify if you want to use external Flash memory and/or RAM. Check the
Use activation buffer for input buffer to make them share the same buffer in order to reduce memory usage.
Analyze again. You can see that the RAM occupation has been significantly reduced (refer to the memory graph for more details).
Check that the model works properly by validating it either on the PC or on the target.
To generate the code for STM32CubeIDE (or Arm® KEIL® or IAR SYSTEMS®) go to
Project manager, specify a project name and location. Select STM32CubeIDE as toolchain, then click
GENERATE CODE on the top right corner.
This generates the necessary code for the whole project. In the present example, only the files related to the neural network are required.
They are located under
YourProjectName\CM7\X-CUBE-AI\App\ and are called
network_config.h. They represent the model and its weight.
3.1.2 Command line interface (Option 2)
The other way to generate the necessary files is to use the command line interface. The main advantage is to produce only the required files.
The documentation related to X CUBE AI is located under
The CLI is called
stm32ai.exe for Windows. It is located under
$HOME/STM32Cube/Repository/Packs/STMicroelectronics/X-CUBE-AI/6.0.0/Utilities/ for UNIX®-based systems.
If there is no
utilities folder, create a CUBE MX project and add Core AI in the Software Package (see section Project generation). This downloads all the necessary files.
For ease of usage, add the folder to your Windows path:
PC $> set CUBE_FW_DIR=C:\Users\<USERNAME>\STM32Cube\Repository PC $> set X_CUBE_AI_DIR=%CUBE_FW_DIR%\Packs\STMicroelectronics\X-CUBE-AI\6.0.0 PC $> set PATH=%X_CUBE_AI_DIR%\Utilities\windows;%PATH%
Once added, go to the folder where you wish to generate the network files in command line (using PowerShell or similar) and run the following command:
PC $> stm32ai.exe generate -m .\model_quant.tflite --allocate-inputs # (change the path to the model if needed).
This creates all the necessary files under the
3.2 Model integration
Now that the C files are generated for your model, integrate them in an already existing project.
In this example, the application is based on the 'Person detection AI function package project.
Launch the STM32CubeIDE project with the
.project located under
FP-AI-VISION1_V3.0.0\FP-AI-VISION1_V3.0.0\Projects\STM32H747I-DISCO\Applications\PersonDetection\MobileNetv2_Model\STM32CubeIDE. Double click it to open STM32CubeIDE.
CM7 subproject and build it. The resulting workspace is shown below:
Replace the model files (
network_config.h) by those generated previously with STM32CubeMX.
Replace them in Windows explorer. Below the file location:
PersonDetection +-- MobileNetv2_Model | +-- Inc | | network.h | | network_data.h | | network_config.h | +-- Src | | network.c | | network_data.c
Change the name of your classes. Go to
fp_vision_app.c and change
output_labels to your class names. Be careful that there are as many labels as your model output size.
Clean your project under STM32CubeIDE with
Make sure that your board is connected to the ST-LINK port and properly powered (set the jumper position to
Build your project and run it with the play button.
A ST-Application pack splash window appears followed by the camera view and the model classification. If either of these window is not displayed properly, go through the wiki article to check if steps have been skipped.