index.js

import { pipeline, env } from 'https://cdn.jsdelivr.net/npm/@xenova/transformers@2.13.0';

// Since we will download the model from the Hugging Face Hub, we can skip the local model check
env.allowLocalModels = false;

// Reference the elements that we will need
const status = document.getElementById('status');
const fileUpload = document.getElementById('upload');
const imageContainer = document.getElementById('container');
const example = document.getElementById('example');

const EXAMPLE_URL = 'https://i.imgur.com/mLvqQws.jpg';

// Create a new image segmentation pipeline
status.textContent = 'Loading model...';
const segmenter = await pipeline('image-segmentation', 'Xenova/face-parsing');
status.textContent = 'Ready';

example.addEventListener('click', (e) => {
    e.preventDefault();
    segment(EXAMPLE_URL);
});

fileUpload.addEventListener('change', function (e) {
    const file = e.target.files[0];
    if (!file) {
        return;
    }

    const reader = new FileReader();

    // Set up a callback when the file is loaded
    reader.onload = e2 => segment(e2.target.result);

    reader.readAsDataURL(file);
});

// Perform image segmentation
async function segment(img) {
    imageContainer.innerHTML = '';
    imageContainer.style.backgroundImage = `url(${img})`;

    status.textContent = 'Analysing...';
    const output = await segmenter(img);
    status.textContent = '';
    output.forEach(renderMask);
}

// Mapping of label to colour
const colours = [
    [234, 76, 76], // red
    [28, 180, 129], // sea green
    [234, 155, 21], // orange
    [67, 132, 243], // blue
    [243, 117, 36], // orange-red
    [145, 98, 243], // purple
    [21, 178, 208], // cyan
    [132, 197, 33], // lime
];

// Render a mask on the image
function renderMask({mask, label}, i) {
    // Create new canvas
    const canvas = document.createElement('canvas');
    canvas.width = mask.width;
    canvas.height = mask.height;
    canvas.setAttribute('data-label', label);
    
    // Create context and allocate buffer for pixel data
    const context = canvas.getContext('2d');
    const imageData = context.createImageData(canvas.width, canvas.height);
    const pixelData = imageData.data;

    // Choose colour based on index
    const [r, g, b] = colours[i % colours.length];

    // Fill mask with colour
    for (let i = 0; i < pixelData.length; ++i) {
        if (mask.data[i] !== 0) {
            const offset = 4 * i;
            pixelData[offset] = r;          // red
            pixelData[offset + 1] = g;      // green
            pixelData[offset + 2] = b;      // blue
            pixelData[offset + 3] = 255;    // alpha (fully opaque)
        }
    }
    
    // Draw image data to context
    context.putImageData(imageData, 0, 0);

    // Add canvas to container    
    imageContainer.appendChild(canvas);
}

// Clamp a value inside a range [min, max]
function clamp(x, min=0, max=1) {
    return Math.max(Math.min(x, max), min)
}

// Attach hover event to image container
imageContainer.addEventListener('mousemove', e => {
    const canvases = imageContainer.getElementsByTagName('canvas');
    if (canvases.length === 0) return;

    // Get bounding box
    const bb = imageContainer.getBoundingClientRect();
    
    // Get the mouse coordinates relative to the container
    const mouseX = clamp((e.clientX - bb.left) / bb.width);
    const mouseY = clamp((e.clientY - bb.top) / bb.height);
        
    // Loop over all canvases
    for (const canvas of canvases) {

        const canvasX = canvas.width * mouseX;
        const canvasY = canvas.height * mouseY;

        // Get the pixel data of the mouse coordinates
        const context = canvas.getContext('2d');
        const pixelData = context.getImageData(canvasX, canvasY, 1, 1).data;

        // Apply hover effect if not fully opaque
        if (pixelData[3] < 255) {
            canvas.style.opacity = 0.1;
        } else {
            canvas.style.opacity = 0.8;
            status.textContent = canvas.getAttribute('data-label');
        }
    }
});

// Reset canvas opacities on mouse exit
imageContainer.addEventListener('mouseleave', e => {
    const canvases = [...imageContainer.getElementsByTagName('canvas')];
    if (canvases.length > 0) {
        canvases.forEach(c => c.style.opacity = 0.6);
        status.textContent = '';
    }
})