Integrate image classifiers

Image classification is a common use of machine learning to identify what an image represents. For example, we might want to know what type of animal appears in a given picture. The task of predicting what an image represents is called image classification. An image classifier is trained to recognize various classes of images. For example, a model might be trained to recognize photos representing three different types of animals: rabbits, hamsters, and dogs. See the introduction of image classification for more information about image classifiers.

Use the Task Library ImageClassifier API to deploy your custom image classifiers or pretrained ones into your mobile apps.

Key features of the ImageClassifier API

• Input image processing, including rotation, resizing, and color space conversion.

• Region of interest of the input image.

• Label map locale.

• Score threshold to filter results.

• Top-k classification results.

• Label allowlist and denylist.

Supported image classifier models

The following models are guaranteed to be compatible with the ImageClassifier API.

• Models created by TensorFlow Lite Model Maker for Image Classfication.

• The pretrained image classification models from TensorFlow Lite Hosted Models.

• The pretrained image classification models on TensorFlow Hub.

• Models created by AutoML Vision Edge Image Classification.

• Custom models that meet the model compatibility requirements.

Run inference in Java

See the Image Classification reference app for an example of how to use ImageClassifier in an Android app.

Step 1: Import Gradle dependency and other settings

Copy the .tflite model file to the assets directory of the Android module where the model will be run. Specify that the file should not be compressed, and add the TensorFlow Lite library to the module’s build.gradle file:

android {
    // Other settings

    // Specify tflite file should not be compressed for the app apk
    aaptOptions {
        noCompress "tflite"
    }

}

dependencies {
    // Other dependencies

    // Import the Task Vision Library dependency (NNAPI is included)
    implementation 'org.tensorflow:tensorflow-lite-task-vision:0.3.0'
    // Import the GPU delegate plugin Library for GPU inference
    implementation 'org.tensorflow:tensorflow-lite-gpu-delegate-plugin:0.3.0'
}

Step 2: Using the model

// Initialization
ImageClassifierOptions options =
    ImageClassifierOptions.builder()
        .setBaseOptions(BaseOptions.builder().useGpu().build())
        .setMaxResults(1)
        .build();
ImageClassifier imageClassifier =
    ImageClassifier.createFromFileAndOptions(
        context, modelFile, options);

// Run inference
List<Classifications> results = imageClassifier.classify(image);

See the source code and javadoc for more options to configure ImageClassifier.

Run inference in C++

// Initialization
ImageClassifierOptions options;
options.mutable_base_options()->mutable_model_file()->set_file_name(model_file);
std::unique_ptr<ImageClassifier> image_classifier = ImageClassifier::CreateFromOptions(options).value();

// Run inference
const ClassificationResult result = image_classifier->Classify(*frame_buffer).value();

See the source code for more options to configure ImageClassifier.

Example results

Here is an example of the classification results of a bird classifier.

Results:
  Rank #0:
   index       : 671
   score       : 0.91406
   class name  : /m/01bwb9
   display name: Passer domesticus
  Rank #1:
   index       : 670
   score       : 0.00391
   class name  : /m/01bwbt
   display name: Passer montanus
  Rank #2:
   index       : 495
   score       : 0.00391
   class name  : /m/0bwm6m
   display name: Passer italiae

Try out the simple CLI demo tool for ImageClassifier with your own model and test data.

Model compatibility requirements

The ImageClassifier API expects a TFLite model with mandatory TFLite Model Metadata. See examples of creating metadata for image classifiers using the TensorFlow Lite Metadata Writer API.

The compatible image classifier models should meet the following requirements:

• Input image tensor (kTfLiteUInt8/kTfLiteFloat32)

  • image input of size [batch x height x width x channels].
  • batch inference is not supported (batch is required to be 1).
  • only RGB inputs are supported (channels is required to be 3).
  • if type is kTfLiteFloat32, NormalizationOptions are required to be attached to the metadata for input normalization.

• Output score tensor (kTfLiteUInt8/kTfLiteFloat32)

  • with N classes and either 2 or 4 dimensions, i.e. [1 x N] or [1 x 1 x 1 x N]
  • optional (but recommended) label map(s) as AssociatedFile-s with type TENSOR_AXIS_LABELS, containing one label per line. See the example label file. The first such AssociatedFile (if any) is used to fill the label field (named as class_name in C++) of the results. The display_name field is filled from the AssociatedFile (if any) whose locale matches the display_names_locale field of the ImageClassifierOptions used at creation time ("en" by default, i.e. English). If none of these are available, only the index field of the results will be filled.