const imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);
    const pixels = imageData.data;
    for (let i = 3, n = canvas.width * canvas.height * 4; i < n; i += 4) {
        pixels[i] = pixels[i] < 127? 0 : 255
    }
    ctx.putImageData(imageData, 0, 0);