JavaScript Canvas を使用して画像のスムーズなサイズ変更を実現するにはどうすればよいですか?

<code class="js">var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var img = new Image();

img.onload = function () {

    // Step 1 - Shrink the image to half its size
    var oc = document.createElement('canvas'),
        octx = oc.getContext('2d');

    oc.width = img.width * 0.5;
    oc.height = img.height * 0.5;
    octx.drawImage(img, 0, 0, oc.width, oc.height);

    // Step 2 - Further reduce the image by half
    octx.drawImage(oc, 0, 0, oc.width * 0.5, oc.height * 0.5);

    // Step 3 - Resize the image back to its intended dimensions
    ctx.drawImage(oc, 0, 0, oc.width * 0.5, oc.height * 0.5,
    0, 0, canvas.width, canvas.height);
}

img.src = "//i.imgur.com/SHo6Fub.jpg";</code>