STT-tensorflow/tensorflow/lite/g3doc/guide/codegen.md

Generate code from TensorFlow Lite metadata

Note: TensorFlow Lite wrapper code generator is in experimental (beta) phase and currently only supports Android.

For TensorFlow Lite model enhanced with metadata, developers can use the TensorFlow Lite Android wrapper code generator to create platform specific wrapper code. The wrapper code removes the need to interact directly with ByteBuffer. Instead, developers can interact with the TensorFlow Lite model with typed objects such as Bitmap and Rect.

The usefulness of the code generator depend on the completeness of the TensorFlow Lite model's metadata entry. Refer to the <Codegen usage> section under relevant fields in metadata_schema.fbs, to see how the codegen tool parses each field.

Generate Wrapper Code

You will need to install the following tooling in your terminal:

pip install tflite-support

Once completed, the code generator can be used using the following syntax:

tflite_codegen --model=./model_with_metadata/mobilenet_v1_0.75_160_quantized.tflite \
    --package_name=org.tensorflow.lite.classify \
    --model_class_name=MyClassifierModel \
    --destination=./classify_wrapper

The resulting code will be located in the destination directory. If you are using Google Colab or other remote environment, it maybe easier to zip up the result in a zip archive and download it to your Android Studio project:

## Zip up the generated code
!zip -r classify_wrapper.zip classify_wrapper/

## Kick off the download
from google.colab import files
files.download('classify_wrapper.zip')

Using the generated code

Step 1: Import the generated code

Unzip the generated code if necessary into a directory structure. The root of the generated code is assumed to be SRC_ROOT.

Open the Android Studio project where you would like to use the TensorFlow lite model and import the generated module by: And File -> New -> Import Module -> select SRC_ROOT

Using the above example, the directory and the module imported would be called classify_wrapper.

Step 2: Update the app's build.gradle file

In the app module that will be consuming the generated library module:

Under the android section, add the following:

aaptOptions {
   noCompress "tflite"
}

Under the dependencies section, add the following:

implementation project(":classify_wrapper")

Step 3: Using the model

// 1. Initialize the model
MyClassifierModel myImageClassifier = null;

try {
    myImageClassifier = new MyClassifierModel(this);
} catch (IOException io){
    // Error reading the model
}

if(null != myImageClassifier) {

    // 2. Set the input with a Bitmap called inputBitmap
    MyClassifierModel.Inputs inputs = myImageClassifier.createInputs();
    inputs.loadImage(inputBitmap));

    // 3. Run the model
    MyClassifierModel.Outputs outputs = myImageClassifier.run(inputs);

    // 4. Retrieve the result
    Map<String, Float> labeledProbability = outputs.getProbability();
}

Accelerating model inference

The generated code provides a way for developers to accelerate their code through the use of delegates and the number of threads. These can be set when initiatizing the model object as it takes three parameters:

• Context: Context from the Android Activity or Service
• (Optional) Device: TFLite acceleration delegate for example GPUDelegate or NNAPIDelegate
• (Optional) numThreads: Number of threads used to run the model - default is one.

For example, to use a NNAPI delegate and up to three threads, you can initialize the model like this:

try {
    myImageClassifier = new MyClassifierModel(this, Model.Device.NNAPI, 3);
} catch (IOException io){
    // Error reading the model
}

Troubleshooting

Getting 'java.io.FileNotFoundException: This file can not be opened as a file descriptor; it is probably compressed'

Under the app module that will uses the library module, insert the following lines under the android section:

aaptOptions {
   noCompress "tflite"
}