A responsive bitmap images thing.
JavaScript CSS
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A responsive bitmap images thing, focusing on markup which describes resources rather than viewport conditions, allowing for a full separation of content and presentation.

<data-scalable> elements contain one thumbnail <img> and any number of larger sources, linked to in <a> elements. The <img> and the <a>s have data-width and data-height attributes which describe the size (in pixels) of the linked file. Like this:

<div data-scalable>
	<img src="thumb.jpg" data-width="100" data-height="100" alt="" />
	<p>View image:</p>
		<li><a href="full.jpg" data-width="1024" data-height="1024">fullsize (1024 x 1024 pixels, 213 kB)</a></li>
		<li><a href="half.jpg" data-width="512" data-height="512">half (48 kB)</a></li>
		<li><a href="quarter.jpg" data-width="256" data-height="256">quarter (14 kB)</a></li>

On load, scalables.js parses this and stores the source URLs & their pixel dimensions.

On load and after any 'resize' or 'orientationchange' event, the script looks at how big the <img> is on the layout and swaps in an appropriately-large source.

I wrote a couple-thousand words about the rationale behind all of it here.


sizing with css

You must explicitly size your image in CSS with width or height styles (but not both, yet!) for this script to do anything useful.

If you don't scale your initial thumbnail (usually up) to fit your layout in CSS, when the script looks at how big the <img> is it will see it at its default (native) dimensions and won't load any of the larger sources.

Practically, if you've been working images into fluid layouts in the past using the conventionally-wise techniques, this will mean writing width: 100%; where you had been writing max-width: 100%;

hiding the links

If you want to hide the links to the image at all of its various sizes (which, maybe you don't?), you must check for Javascript support first and only hide if you're reasonably certain that the script will run.

If you're not already checking for JS with something like modernizr, add this to your page (above the data-scalables):

<script>document.getElementsByTagName('html')[0].className += " js"</script>

Then you can hide the links like this:

.js [data-scalable] *:not(img) {
	display: none;

retina & co.

Have opinions about how you want to deal with hi-DPI displays? You'll want to tweak the fuzzyFactor. From the comments:

// fuzzyFactor!
// A number between 0-1 that determines how we want to deal with device-pixel-ratios above 1
// lower = more quality, higher = faster loads
// 0 = images will always render as crisply as the device will allow (effective image resolution of 2x @ 2x, 3x @ 3x, etc.)
// 1 = screw device pixels, I only care about css-px (effective image resolution of 1x @ 2x, 1x @ 3x, etc.)
// 0.5 = eric's pick (effective image resolution of 1.414x @ 2x, 2x @ 4x, 4x @16x...)
// note! that these are *worst-case resolutions* - once an image is stretched such that its pixel-density falls below this threshold, we load a bigger one

scalable <picture>s

"scalable-pictures.js" is an experiment in marking up scalable images with the proposed <picture> and <source> elements.


"scalable-tag.rb" is a Jekyll plugin which makes authoring scalables.js-compliant markup and generating downsized images as easy as pointing to the full-sized image in a custom Jekyll tag and letting the plugin do the rest.

"Make Scalable Image.jsx" is a Photoshop script that I hacked together to generate scalables.js markup and source-files.


Particular thanks are due to Paul Robert Lloyd and Josh Emerson for the actual code that this grew out of.