preprocessCanvas = (canvas) => {
let tensor = tf.browser.fromPixels(canvas);
console.log(tensor.data());
tensor = tf.image.resizeNearestNeighbor(tensor, [28, 28])
tensor = tensor.mean(2)
tensor = tf.reshape(tensor, [1, 28*28])
tensor = tensor.toFloat();
console.log('input:', tensor.data());
return tensor;
}