Background instead of inline images for mobile optimization with media queries?

Question

Ive mobile optimised my site with media queries. Everything looks how I would like it to but unnecessary images (as they're hidden with css) are being downloaded, slowing page loading times.

The easiest solution to this seems to be to replace as many inline images as I can with divs with background images. Then I can hide the div's with media query css for the mobile version.

I know there are potential downsides to this, outlined well in this post: When to use IMG vs. CSS background-image?

So the company logo, pictures of staff, etc will stay as inline images.

Are there any issues to my approach I havn't considered? Ive read a lot about mobile optimisation, particularly with media queries, and I havn't heard of anyone doing this even though it seems quite an obvious solution where images could be inline or background.

Note, ive done some experiments with iPhones and Android (im waiting to get some Blackberrys) and I know to stop background images downloading I need to set display none to the div's parent, not the div with the background image itself.

Note2, in an ideal world sites would probably have been built as mobile first but in this situation (and often in others) there is a limit to how much the original site can be modified.

Thanks

Answer 1

Unfortunately, there are no great answers for the problems you’re trying to solve.

First, you have the option of moving everything from img tags to css background images. As you note, you have to be careful of losing semantic meaning by doing so.

But even if you can move to background images without losing semantic value, it is still not going to be 100% reliable. I wrote a series of tests last summer. I retested them last week in preparation for the chapter in our book on mobile first responsive web design. The tests are located at http://www.cloudfour.com/examples/mediaqueries/image-test/.

Unfortunately, Android fails every one of those techniques. You can see it downloading multiple copies of the image files via Blaze’s mobile test: www.blaze.io/mobile/result/?testid=111031_96_316

UPDATE 3 Nov 2011: I’m currently trying to reconcile inconsistent results between what I see on Blaze and what I see using the same device in person. On my local Nexus S, it passes the fifth css test which limits the imgs by putting them inside the media queries. I watched the apache logs and confirmed the device only downloads one image instead of two for test 5. Blaze is running 2.3.3. My phone is running 2.3.6.

This is true for Android 2.2, 2.3 and 3.0. Hopefully, 4.0 will incorporate the webkit fixes that prevent this behavior: bugs.webkit.org/show_bug.cgi?id=24223

BTW, this seems to conflict with your comment about testing setting the parent div to display:none on Android. If you’re getting different results, I’d love to hear about it.

If you keep them as img tags, what are your options? On this topic, I have written a multi-part series. The second part in the series provides an in-depth look at the different techniques: http://www.cloudfour.com/responsive-imgs-part-2/

Again, none of the solutions are great. If you want something that is simple and will work most of the time, I’d go for adaptive-images.com. Or route images through Sencha.io SRC until we have a better solution for this problem.

BTW, sorry for having so many links that aren’t actually links. This is my first response on stackoverflow and it will only allow me to include two links.

Answer 2

Why not do a mobile first approach and then use media queries to enhance bigger screens.

Also you can use media queries to serve specific CSS files.

With the inline images I have tried a script block in the head and immediately after the opening body tag, which runs only for mobile devices (detect via classname added to body, or presence of a media query CSS file) that find all inline images with a certain class and empty the src attribute.

see here Prevent images from loading

<script type="text/javascript" charset="utf-8">
    $(document).ready( function() { $("img").removeAttr("src"); } );
</script>

another way is to use url re-writing with mod rewrite and .htaccess or url rewrite module for iis. redirect user agent strings for mobiles to a small blank image.

see: A way to prevent a mobile browser from downloading and displaying images

RewriteCond %{HTTP_USER_AGENT} (nokia¦symbian¦iphone¦blackberry) [NC] 
RewriteCond %{REQUEST_URI} !^/images/$
RewriteRule (.*) /blank.jpg [L]

you can improve the above by loading your inline images from a different sub-domain and rewriting only those for mobile, as you don't want to rewrite all images (logo etc.)