Add mini web demo

demo/src/components/helpers/maskUtils.tsx

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+// Functions for handling mask output from the ONNX model
+
+// Convert the onnx model mask prediction to ImageData
+function arrayToImageData(input: any, width: number, height: number) {
+  const [r, g, b, a] = [0, 114, 189, 255]; // the masks's blue color
+  const arr = new Uint8ClampedArray(4 * width * height).fill(0);
+  for (let i = 0; i < input.length; i++) {
+
+    // Threshold the onnx model mask prediction at 0.0
+    // This is equivalent to thresholding the mask using predictor.model.mask_threshold
+    // in python
+    if (input[i] > 0.0) {
+      arr[4 * i + 0] = r;
+      arr[4 * i + 1] = g;
+      arr[4 * i + 2] = b;
+      arr[4 * i + 3] = a;
+    }
+  }
+  return new ImageData(arr, height, width);
+}
+
+// Use a Canvas element to produce an image from ImageData
+function imageDataToImage(imageData: ImageData) {
+  const canvas = imageDataToCanvas(imageData);
+  const image = new Image();
+  image.src = canvas.toDataURL();
+  return image;
+}
+
+// Canvas elements can be created from ImageData
+function imageDataToCanvas(imageData: ImageData) {
+  const canvas = document.createElement("canvas");
+  const ctx = canvas.getContext("2d");
+  canvas.width = imageData.width;
+  canvas.height = imageData.height;
+  ctx?.putImageData(imageData, 0, 0);
+  return canvas;
+}
+
+// Convert the onnx model mask output to an HTMLImageElement
+export function onnxMaskToImage(input: any, width: number, height: number) {
+  return imageDataToImage(arrayToImageData(input, width, height));
+}