tfjs-examples

TensorFlow.js Deployment Example : Browser Extension

This example creates a Chrome extension (v3), enabling users to right-click on images within a web page, and perform multi-class object detection on them. The extension will apply a MobileNetV2 classifier to the image, and then print the predicted class on top of the image.

To build the extension, use the command:

yarn
yarn build

To install the unpacked extension in chrome, follow the instructions here. Briefly, navigate to chrome://extensions, make sure that the Developer mode switch is turned on in the upper right, and click Load Unpacked. Then select the appropriate directory (the dist directory containing manifest.json);

If it worked you should see an icon for the TF.js mobilenet Chrome extension.

Using the extension

Once the extension is installed, you should be able to classify images in the browser. To do so, navigate to a site with images on it, such as the Google image search page for the term “tiger” used here. Then right click on the image you wish to classify. You should see a menu option for Classify image with TensorFlow.js. Clicking that image should cause the extension to execute the model on the image, and then add some text over the image indicating the prediction.

Removing the extension

To remove the extension, click Remove on the extension page, or use the Remove from Chrome... menu option when right clicking the icon.

Development notes

Here is how the extension works at a high level:

• A service worker src/service_worker.js is created that bundles the TFJS union package and the mobilenet model. We use a bundler (parcel) to bundle everything together so no external scripts are loaded at runtime. This is to comply with the requirement of Chrome Extension V3. Note that a service worker can still load external resources (such as TFJS models).
• Create a context menu item in the service worker that operates on images. When the menu item is clicked, the image src is sent to the content script for processing. Note that in a service worker, DOM objects (e.g. Image, document, etc) are not available.
• After the content script content.js receives the image src, it loads the image, renders the image on an OffscreenCanvas, gets the ImageData from the canvas, and sends the data back to the service worker.
• After the service worker receives the image data, it runs the mobilenet model with the data, and gets the prediction results. It then sends to results back to the content script for display.
• After the content script receives the results, it overlays the results on top of the original image.

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