Things about Web Images I Just Learned

I thought I knew everything you needed to know about Web images.  But, of course, I didn't. Here's what I just learned when launching the new icon bar on the homepage of Duck Duck Go. We wanted the it to function sort of like the Apple dashboard (and on the Web like Schmedley's bottom bar).

  • img{-ms-interpolation-mode:bicubic}. Short version: if you resize images dynamically, they will look bad on IE unless you put this in your CSS.

    Longer version:  We ended up using the YUI Animation Library to do the animation.  But no matter how we did it using 1 image, it always looked terrible on IE.  Even if we used an image exactly as big as the big size, and did the smaller image exactly half of the bigger size (which should be easy to resize), it still looked bad.

    So then we tried using two images, which sort-of worked, but had its own issues.  Sometimes it would slow down the animation. It used almost double the image size and requests (a big no-no), and the actual resizing still looked bad (as opposed to the endpoints)!

    This was unacceptable, so I decided to dig deeper on the Web about this issue.  It turns out modern browsers use Bicubic interpolation to resize images and make them look good in the process. For whatever reason, IE7+ has decided to turn it off by default. I'm guessing this is because it takes some processing power, but it renders resized images looking terrible so I personally don't think this is a good trade off.  Anyway, if you add that above CSS to your page, IE7+ will use this method and your images will look good. I suppose I never hit this before because usually you shouldn't be resizing images dynamically. But there are cases where you want to do it...

    Unfortunately, it still doesn't work for IE6, on which you need to use the good ol' AlphaImageLoader (sizingMethod='scale') if you want to support that browser.

  • Photoshop/Illustrator's 'Save for Web...' does not fully optimize. Perhaps my versions of Photoshop and Illustrator are too old, but I suspect this is still the case with the newer versions. I pretty much used these blind, assuming they were optimizing correctly. And don't get me wrong, it does a decent job, but its just not the best. Instead, run your images through Yahoo!'s site.

  • If you really do not need PNG-24, use PNG-8. PNG-8 is really a better GIF. But it is limited in color palette and transparency with respect to PNG-24. That being said, often you don't need the difference, especially for things like icons. When you can, use PNG-8 because you'll get much smaller file sizes.

    That being said, you might think you need PNG-24 when you really don't. I did. I had these icons made that had full transparency. I knew, however, they were going to be on a white background, so I really didn't need all the transparency. Yet when I tried to save it as PNG-8, it just looked bad. The colors were all off. So it made me think that I needed PNG-24, but in reality it was Photoshop's optimization stuff that was being poor. In their defense, I wasn't helping them out by setting the white background ahead of time, which leads me to:

  • If you want to save a PNG-24 image as PNG-8, put in the background first. Once I made a white background layer, Photoshop then did a great job of saving it as PNG-8. And in fact, I could reduced the file size even more by using even less than 256 colors. Of course, I still had to run it through

  • CSS sprites may reduce your page load (and image size further). CSS sprites are a way to group your images into one big file and then split them into separate files via CSS. There is a useful Web site to help you make them at I couldn't figure out how to use it with my resizing requirements, but in the general case it should be at least tried, especially for icons where the color palette for your icons are similar. You get a win in image size. But you get a bigger win in reducing HTTP requests.

  • Custom icons are not that expensive. We got $40 custom icons and $10 recolored icons from We talked to other icon designer firms as well, and prices were similar. Full disclosure: we created more than 3 icons (7), so we got a bit of a bulk discount. I did have a bad experience with, however. So I'd stay away from them.
For more image optimization tips, check out Yahoo!'s presentation.

Update: additional comments can be found here.


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I'm the Founder & CEO of DuckDuckGo, the search engine that doesn't track you. I'm also the co-author of Traction, the book that helps you get customer growth. More about me.