HTML canvas image is far lower quality than original image. Why? [duplicate]

Question

I have a simple HTML document with an image and a canvas element. The image src is just some high quality image found online, just to illustrate my point. When I try to draw the image onto the canvas, the resulting canvas image is very pixelated and low quality. I can't seem to figure out why. Similar questions have been asked here, but I couldn't find an answer that seemed to solve the problem. If someone finds another post with a working answer, please let me know. Any help is greatly appreciated. Thanks in advance!

Here is the JSfiddle with the code: https://jsfiddle.net/vey309b0/5/

HTML:

<p>the original image:</p>
<img id="img_cam" src="https://4.bp.blogspot.com/k8IX2Mkf0Jo/U4ze2gNn7CI/AAAAAAAA7xg/iKxa6bYITDs/s0/HOT+Balloon+Trip_Ultra+HD.jpg" width="400">
<p>the canvas with drawn image:</p>
<canvas id="imgcanvas" width="400"></canvas>

JavaScript:

var canvas = document.getElementById("imgcanvas");
var img_can = document.getElementById("img_cam");
var ctx = canvas.getContext("2d");
var imgWidth = img_can.width;
var imgHeight = img_can.height;
canvas.width = imgWidth;
canvas.height = imgHeight;
ctx.drawImage(img_can, 0, 0, imgWidth, imgHeight);

Answer 1

Set the width and the height of the canvas to the naturalWidth and naturalHeight of the image, and then use CSS to constrain the canvas size.

var canvas = document.getElementById("imgcanvas");
var ctx = canvas.getContext("2d");
var img_can = document.getElementById("img_cam");
img_can.onload = function() {
  canvas.width = this.naturalWidth;
  canvas.height = this.naturalHeight;
  ctx.drawImage(this, 0, 0);
};
img_can.src = img_can.getAttribute('data-src');

<p>
the original image:
</p>
<img id="img_cam" data-src="https://4.bp.blogspot.com/-k8IX2Mkf0Jo/U4ze2gNn7CI/AAAAAAAA7xg/iKxa6bYITDs/s0/HOT+Balloon+Trip_Ultra+HD.jpg" width="400">
<p>
the canvas with drawn image:
</p>
<canvas id="imgcanvas" style="width:400px;"></canvas>

You should also really be doing this work in an onload listener on the img tag.