Apple just announced a brand new iMac with a Retina display — Apple’s term for a display with pixels small enough that they can’t under normal use be detected by the human eye. Retina started on the iPhone, graduated to the iPad, then moved to the MacBook Pro — but now it’s moving to Apple’s giant desktop screens. We’re talking 14.7 million pixels. (The original iPhone had 153,600 — 1/96th as many.)

It looks like a very nice piece of kit, but it’s worth note to publishers because the iMac is probably the single most common computer used by web designers. (I’m typing this on one.) And the downside of a Retina display is that your old website graphics, designed for one-fourth as many pixels, will look a little fuzzy. So a lot of designers will be tempted to replace their existing images with ones 4× as large so they’ll look “right” on their screens. Even more important, their bosses will someday soon get these glorious screens and ask a dev: Why is my website fuzzy on my computer? You saw some of this when the Retina MacBook Pro, but this is the next step. (And of course, non-Apple desktop and laptop computers will continue to get more pixel-dense displays, just as phones and tablets have.)

Bigger images are nice in every way except file size. The weight of the average web page has been on a steady march northward, sitting now more than 15× that of a web page 10 years ago and 50 percent larger than just a year ago. Most of that page weight is images. And this new iMac will push a lot of nice 125K images into 500K bandwidth-cloggers. That’d probably fine on your beautiful new desktop on a fat broadband pipe, but it’ll mean your website will get substantially slower on a phone — just as even more of your audience switches to phones.

This doesn’t have to happen, of course. CSS media queries allow you to serve different images to devices with different pixel ratios. And solutions for responsive images are in various stages of progress. (We use Picturefill all over this site and have been happy with it.) SVG gets better all the time, and icon fonts can solve problems in a pinch. (This book, coming out soon, will tell you what you need to know.)

But those methods rely on coders using best practices, and not everyone does. So watch your site and see if page weight starts to creep up not long after a few large Apple boxes get dropped off in graphics.

“The median page has slowed down by 23% in just twelve months.” Performance findings on top ecommerce sites: http://t.co/DISLu7HCZZ

— Responsive Design (@RWD) October 14, 2014

Apple Announced New iMac That Will Make You Feel Bad About Your Website Graphics

— Joshua Benton (@jbenton) October 16, 2014

What he said —> MT @jbenton: Web designers getting the retina iMac will increase the average weight of a web page 300K, minimum

— Adam Schweigert (@aschweig) October 16, 2014

@jbenton it is going to hasten the need for <picture> or some such. /cc @davatron5000

— Travis Swicegood (@tswicegood) October 16, 2014

@jbenton Responsive images can't get here fast enough. In the meantime, picturefill the hell out of that stuff.

— John Hancock (@Hancock_JohnD) October 16, 2014