Crisp pixel art look with image-rendering

This article discusses a useful technique for giving your canvas/WebGL games a crisp pixel art look, even on high definition monitors.

The concept

Retro pixel art aesthetics are getting popular, especially in indie games or game jam entries. But since today's screens render content at high resolutions, there is a problem with making sure the pixel art does not look blurry. Developers have been manually scaling up graphics so they are shown with blocks that represent pixels. Two downsides to this method are larger file sizes and compression artifacts.

small pixelated man small pixelated man larger pixelated man
original size 4x size 4x size (scaled with an image editor)
none vendor's algorithm nearest-neighbor algorithm

A CSS-based solution

The good news is that you can use CSS to automatically do the up-scaling, which not only solves the blur problem, but also allows you to use the images in their original, smaller size, thus saving download time. Also, some game techniques require algorithms that analyze images, which also benefit from working with smaller images.

The CSS property to achieve this scaling is image-rendering. The steps to achieve this effect are:

  • Create a <canvas> element and set its width and height attributes to the original, smaller resolution.
  • Set its CSS width and height properties to be 2x or 4x the value of the HTML width and height. If the canvas was created with a 128 pixel width, for example, we would set the CSS width to 512px if we wanted a 4x scale.
  • Set the <canvas> element's image-rendering CSS property to pixelated, which does not make the image blurry. There are also the crisp-edges and -webkit-optimize-contrast values that work on some browsers. Check out the image-rendering article for more information on the differences between these values, and which values to use depending on the browser.

An example

Let's have a look at an example. The original image we want to upscale looks like this:

Pixelated night scenery of a cat on the edge off a cliff with little hearts above his head, behind him a big full moon. With a black background, white text is displayed at the bottom of the image saying: in love with the moon.

Here's some HTML to create a simple canvas:

<canvas id="game" width="128" height="128">A cat</canvas>

CSS to size the canvas and render a crisp image:

canvas {
  width: 512px;
  height: 512px;
  image-rendering: pixelated;

And some JavaScript to set up the canvas and load the image:

// Get canvas context
const ctx = document.getElementById("game").getContext("2d");

// Load image
const image = new Image();
image.onload = () => {
  // Draw the image into the canvas
  ctx.drawImage(image, 0, 0);
image.src = "cat.png";

This code used together produces the following result:

Note: Canvas content is not accessible to screen readers. Include descriptive text as the value of the aria-label attribute directly on the canvas element itself or include fallback content placed within the opening and closing canvas tag. Canvas content is not part of the DOM, but nested fallback content is.