When OS X icons maxed out at 128×128 pixels, it was a lot easier to make them. Icon designers made 128, 32, and 16px resources. We only had to make those three. If you wanted to support Windows XP, maybe you added 48px.
Windows Vista added 256px icon resources around the same time Mac OS X added 512px resources to support the Cover Flow view in Finder. While 512px sounds like “only” 400% the size, it is, in fact …16 times the amount of pixels. That changes things radically.
You can get away with a lot of fudging at lower resolutions. You don’t have to be as precise. On lower-resolution displays where there were gaps between physical pixels, your brain fills in details that were never there. Things looked better; at least we remembered them better.
When retina displays were introduced, the situation got significantly “worse,” because every resource needed a double-size version. Consider this: you can fit sixty-four 128×128 icons inside just one 1024×1024 image.
For the sake of comparison, 128×128 icons contain “just” 16,384 pixels, whereas 1024×1024 icons contain a whopping 1,048,576 pixels.
And while it may initially seem like the total resource count merely increased to include 1024 and 512px resources, the ICNS filetype and .iconset resource folders now support—and in some cases require—double-size assets for every physical size. It’s not just the bigger sizes that were created, but new smaller sizes too.
That means there are two 32×32 assets, one is 32×32 and the other is technically 16×16@2x. And the 32×32 resource now has a double-size 32×32@2x at a brand-new resolution, 64×64. What used to be only three resources is now 10, with 7 unique pixel sizes. What to do about those new sizes?
When retina resolutions were new, many of us pondered whether a 2x resource should be drawn differently than a 1x resource with the same pixel dimensions. For example, should a 2x resource be a “doubled” version of the 16px icon, with thicker strokes? Or should it appear to have sharper lines than its 1x counterpart? There’s never been a clear answer, perhaps because over the years, the art of making icons at multiple hinted sizes vanished.
To be sure, Apple designers often still create hinted sizes for macOS icons, but you won’t see many third party apps that bother anymore. Did it just become too much to bear? Developers often seek to automate the process by simply scaling one big image to all the smaller required sizes. Even designers at big software companies might do the same.
But it’s not just icons for apps that lost this element of the craft, macOS icons made for fun kinda disappeared too. Some people still do it, myself included. But what once took a half-hour can take several hours. An increased minimum icon size coupled with excessive asset production takes a lot of “fun” out of making icons as art.
Making an icon or two here and there is still quite fun. But making large sets can feel a lot more like busywork. Twenty years ago, making 60—or more—individual icons to create a “system replacement” set was indeed a lot of work, but doing it today would be significantly more effort. A lot of icon artists moved laterally into other areas, transferring their skills into other, similar things.
Over the years, Apple made changing icons on macOS more difficult with every release and removed the downloads page from their website. (Yes! Apple used to have a downloads section of their site with lots of things you could download, including software, but also a section for custom icons and screensavers! For example, here’s an archived page for my Pirates of the Caribbean icons.)

It’s been almost sixteen years since I wrote one of my very first blog posts, The Importance of Icon Sizes. Much of what I said then remains true today:
It is just as important to create additional detail in a large icon as it is to remove excess detail in a small icon.
As an aside, it does make me wonder if at least part of the reason we saw a huge design shift with iOS 7 and macOS Big Sur was because of how much more effort was required to create visually-rich assets. It is a lot easier to just put a glyph on top of a linear gradient.
Though the effort required to make nice, rich visual icons at multiple hinted sizes often goes unnoticed, I still take pride in doing it. I love futzing with those smaller sizes, even for 1x versions that may never be seen in modern computing. I like adding detail into the 1024px resource, even if no one scales the icon that large. To me, that stuff is important. Even if no one sees it.

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