TensorFlow Lite Python object detection example with Pi Camera

This example uses TensorFlow Lite with Python on a Raspberry Pi to perform real-time object detection using images streamed from the Pi Camera. It draws a bounding box around each detected object in the camera preview (when the object score is above a given threshold).

Although the TensorFlow model and nearly all the code in here can work with other hardware, the code uses the picamera API to capture images from the Pi Camera. So you can modify those parts of the code if you want to use a different camera input.

At the end of this page, there are extra steps to accelerate the example using the Coral USB Accelerator, which increases the inference speed by ~10x.

Set up your hardware

Before you begin, you need to set up your Raspberry Pi with Raspbian (preferably updated to Buster).

You also need to connect and configure the Pi Camera.

And to see the results from the camera, you need a monitor connected to the Raspberry Pi. It's okay if you're using SSH to access the Pi shell (you don't need to use a keyboard connected to the Pi)—you only need a monitor attached to the Pi to see the camera stream.

Install the TensorFlow Lite runtime

In this project, all you need from the TensorFlow Lite API is the Interpreter class. So instead of installing the large tensorflow package, we're using the much smaller tflite_runtime package.

To install this on your Raspberry Pi, follow the instructions in the Python quickstart. Return here after you perform the pip install command.

Download the example files

First, clone this Git repo onto your Raspberry Pi like this:

git clone https://github.com/tensorflow/examples --depth 1

Then use our script to install a couple Python packages, and download the MobileNet model and labels file:

cd examples/lite/examples/object_detection/raspberry_pi

# The script takes an argument specifying where you want to save the model files
bash download.sh /tmp

Run the example

python3 detect_picamera.py \
  --model /tmp/detect.tflite \
  --labels /tmp/coco_labels.txt

You should see the camera feed appear on the monitor attached to your Raspberry Pi. Put some objects in front of the camera, like a coffee mug or keyboard, and you'll see boxes drawn around those that the model recognizes, including the label and score for each. It also prints the amount of time it took to perform each inference in milliseconds at the top-left corner of the screen.

For more information about executing inferences with TensorFlow Lite, read TensorFlow Lite inference.

Speed up the inferencing time (optional)

If you want to significantly speed up the inference time, you can attach an ML accelerator such as the Coral USB Accelerator—a USB accessory that adds the Edge TPU ML accelerator to any Linux-based system.

If you have a Coral USB Accelerator, follow these additional steps to delegate model execution to the Edge TPU processor:

1. First, be sure you have completed the USB Accelerator setup instructions.

2. Now open the detect_picamera.py file and add the following import at the top:

   from tflite_runtime.interpreter import load_delegate
   

   And then find the line that initializes the Interpreter, which looks like this:

   interpreter = Interpreter(args.model)
   

   And change it to specify the Edge TPU delegate:

   interpreter = Interpreter(args.model,
       experimental_delegates=[load_delegate('libedgetpu.so.1.0')])
   

   The libedgetpu.so.1.0 file is provided by the Edge TPU library you installed during the USB Accelerator setup in step 1.

3. Finally, you need a version of the model that's compiled for the Edge TPU.

   Normally, you need to use use the Edge TPU Compiler to compile your .tflite file. But the compiler tool isn't compatible with Raspberry Pi, so we included a pre-compiled version of the model in the download.sh script above.

   So you already have the compiled model you need: mobilenet_ssd_v2_coco_quant_postprocess_edgetpu.tflite.

Now you're ready to execute the TensorFlow Lite model on the Edge TPU. Just run detect_picamera.py again, but be sure you specify the model that's compiled for the Edge TPU (it uses the same labels file as before):

python3 detect_picamera.py \
  --model /tmp/mobilenet_ssd_v2_coco_quant_postprocess_edgetpu.tflite \
  --labels /tmp/coco_labels.txt

You should see significantly faster inference speeds.

For more information about creating and running TensorFlow Lite models with Coral devices, read TensorFlow models on the Edge TPU.