[This almost got named “macOS Sierra’s a JPEG-2000 hater”.]
A few years back, when Retina-fying Mac imagery was all the rage, we faced a little conundrum related to how well we supported older versions of Mac OS X in Audiobook Builder and CheckBook: those older versions of Mac OS X didn’t play nicely when ICNS files, which hold all the various representations of a particular icon, went over a certain size. Or maybe it was just when one or more representations were over a certain size. Whatever. Somehow, the data for the larger representations that Retina Displays love had to slim down a bit and the way we heard other developers were doing it was to convert those representations from PNG to JPEG-2000. We did it. It worked. We shipped. These slimmer ICNS files ended up in both the Splasm Store and Mac App Store versions of Audiobook Builder, as well as in the Splasm Store versions of CheckBook and CheckBook Pro. All was well.
Then Apple released macOS 10.12.2 and we heard the icons in the Splasm Store versions of all three applications were rendering strangely. Washed out, streaky, freaky rendering in the Finder and even in parts of the applications themselves. It wasn’t happening to everyone, but that looked to be a caching issue. Sooner or later, if you have one of these applications, you’ll see the strangeness.
That JPEG-2000 diet we put the ICNS files is the culprit, but we no longer need that trick, anyway, since none of these applications are supported on those older versions of Mac OS X anymore.
So updated icons are on the way, but if you need them sooner than the official release, let us know. We’ve got what you need and can send a link to a pre-release build with the icons you crave.