Responsive Images with srcset & Craft

A simple solution to produce responsive images with srcset and Craft.

Tommy recently wrote about responsive background images in Craft, but I wanted to follow up about how we used the <img> element and srcset to build responsive images on this very site (powered by Craft).

We have a Matrix field that powers a lot of the content on the site, and one of the blocks is an image block. A user can upload an image of any size, so I wanted to figure out some way to make that image responsive.

I decided this would be a good opportunity to utilize srcset to output a couple of different image sizes to speed up the page load on smaller devices. We determined that capping the images at 2000 pixels wide would be reasonable, and then I created half and quarter size image crops. Here is what the template looks like:

{% set image = block.image[0] %}
{% set full = (image.width > 2000) ? 2000 : image.width %}
{% set half = round(full / 2) %}
{% set fourth = round(full / 4) %}

  <img src="{{ image.url({ width: half }) }}" alt=""
       srcset="{{ image.url({ width: fourth }) }} {{ fourth }}w,
               {{ image.url({ width: half }) }} {{ half }}w,
               {{ image.url({ width: full }) }} {{ full }}w"
       sizes="(min-width: {{ half + 1 }}px) {{ full }}px,
              (min-width: {{ fourth + 1 }}px) {{ half }}px,

Then, to see what this looks like rendered as HTML with a 2000 pixel image:

  <img src="" alt=""
       srcset=" 500w,
       sizes="(min-width: 1001px) 2000px,
              (min-width: 501px) 1000px,

This is just a super simple example; you could easily get more complex by producing more transforms or using additional media queries. Even though it's a small improvement, images are what produce the most bloat on sites these days.

Trevor Davis

Trevor is a front-end development director who specializes in writing bulletproof code for clients including the World Wildlife Fund, the NFLPA, and the Human Rights Campaign.

More articles by Trevor

Sign up for The Viget Newsletter

Nobody likes popups, so we waited until now to recommend our newsletter, a curated periodical featuring thoughts, opinions, and tools for building a better digital world. Read the current issue.