Responsive Images

Bruce Lawson

Responsive Images

Bruce Lawson, Opera Software

bruce in front of 'HTML' sign

New HTML thingies


quick to react in the way that is needed, suitable, or right for a particular situation
Macmillan Dictionary


quick to react in the way that is needed, suitable, or right for a particular situation
Macmillan Dictionary

Speed is part of ‘responsive’

0.5 second delay = 20% drop in traffic (Google). 100ms delay = 1% decrease in sales (Amazon)
How a Slow Website Impacts Your Visitors and Sales
1 sec delay causes 7% drop in conversions (GlassesDirect)
Tag Management Blog
5 sec improvement in page load time resulted in 5% – 12% increase in revenue (Shopzilla)
Velocity Conference

The problem with images

Images are big

average page-weight is 1.9MB, of which 1.2MB is images

…and getting bigger.

Over last 8 years, number of images per page has remained quite static but size of images has increased dramatically

The ‘retina’ question

Q: How can I send super high-quality (=huge) images to retina devices but normal quality images (=smaller file size) to devices with non-retina/ small screens?

The ‘retina’ answer

A: I can't.

<img src="blah.jpg">

CSS to the rescue?

<img id=lovely src=mankini.png
  alt="Bruce in a mankini">

@media all and (max-width:320px) {
 #lovely {content: url(lowres-mankini.png);}

Double download - WTF?

Both images are downloaded!
A cartoon fairyland

The Browser Fairy Queen

A fairy queen turning some HTML into a DOM tree

Image Helper Elves

Elves flying off to get images


One study showed preloading makes pages load ~20% faster.

I think preloading is the single biggest performance improvement browsers have ever made.

Steve Souders

HTML5 video with MQs

<source src=foo-lowres.webm media="max-width:480px">
<source src=foo-hires.webm>
  <!-- Fallback content -->

Notes on Adaptive Images (yet again!) (Dec 2011)

My <picture> strawman

<source src=foo-lores.jpg media="max-width:480px">
<source src=foo-full.jpg>
  <!-- Fallback content -->
  <img src="foo-lores.jpg" alt="…">
responsive images community group


Mat Marquis
Marcos Caceres
Tab Atkins
Simon Pieters
Yoav Weiss

Optimising for high-dpi screens

srcset x descriptor

<img src="normal.jpg"
srcset="hi-res.jpg 2x"

srcset x descriptor

<img src="normal.jpg"
srcset="hi-res.jpg 2x, super-res.jpg 3x"

This is not you

Browser Fairy Queen
Opera Mini settings options (allows you to select image quality)

Stretchy ("responsive") images


<img src="mankini.png" alt="lovely">
img {max-width:100%;

Makes the browser work

On the test page with 6x images (not unusual at the moment on many responsive sites), the combination of resizes and decodes added an additional 278ms in Chrome and 95.17ms in IE (perhaps more …) to the time it took to display those 10 images.
Why We Need Responsive Images: Part Deux
- Tim Kadlec

The w descriptor

<img src="medium.png"
	srcset="big.png 960w,
	small.png 240w">

Spec change!

<img src="medium.png"
	srcset="big.png 960w,
	small.png 240w"

Changing image sizes

	src="opera-400.jpg" alt="The Oslo Opera House"
	sizes="(min-width: 640px) 60vw, 100vw"
	srcset="opera-200.jpg 200w,
			opera-800.jpg 800w,
			opera-1200.jpg 1200w,
			opera-2000.jpg 2000w">

Sending different image formats

Current formats (Jan '15)

pie chart of image formats used in Jan 2015 websites: JPG 47%, PNG 29%, GIF 22%, Other 2%


WebP lossless images are 26% smaller in size compared to PNGs. WebP lossy images are 25-34% smaller in size compared to JPEG images
More, conversion tools

HTML5 video

	<source src=foo.webm type=video/webm>
	<source src=foo.mp4 type=video/mp4>
	  <!-- Fallback content -->

Real <picture> format switch

  <source srcset="tree.webp" type="image/webp">
  <img src="tree.jpg" alt="tree">

webp= 25K, jpg=38K

<picture> magic

<picture> just magically changes which image the <img> pulls in to display.

Check currentSrc in JavaScript to see what’s chosen by the browser.

Art direction

art directed images on variety of devices

<picture> for art direction

    media="(min-width: 1024px)"
  <img src="whitehouse-closeup.jpg"
    alt="Dog in front of white house">


  • Opera
  • Chrome
  • Firefox 38 (12 May 2015)
  • IE: srcset "in development", <picture> "under consideration"
  • Safari: srcset x descriptors (iOS 8.1), <picture> ??

Progressive enhancement

Because responsive images require use of <img src>, no-one gets a worse experience than they do now.

fairies and princesses, 'they all lived happily ever after'