Today, we’re excited to introduce an all-new Image Comparison in Kaleidoscope 6.4 Beta! Now, before you scroll down looking for a list of shiny new features — don’t get too excited just yet. There are some lovely improvements (we’ll get to those), but the real story here is under the hood.
This release is all about getting the foundation right. We’ve rebuilt the Image Comparison on a completely new technology stack. That means it’s faster, more reliable, and ready for future innovation. From here on out, adding new features will be easier.
Goodbye OpenGL, Hello Metal
Since version 1.0, Kaleidoscope has used an OpenGL-based implementation for the Image Comparison. That era is now officially over.
While the new version preserves the functionality you’re used to, not a single line of old code remains. We’ve moved to AppKit for user interaction, Core Image for the image pipeline, and Metal for rendering. And in case you’re wondering — no, we didn’t even try to do this in SwiftUI.
This was a big project quietly running in the background for months. It started with Christopher experimenting in Claude Code — writing, iterating, and rewriting — combining his own knowledge and experience with the AI’s ability to rapidly test ideas. Eventually, he landed on a prototype that fulfilled all our needs. When the time came to merge that work into Kaleidoscope, Michael had the honor of wrestling with AI-generated code, which, let’s just say, didn’t always meet his expectations for good code.
Many weeks and a lot of polish later, we’re ready to share a public beta of Kaleidoscope 6.4.
Why a Public Beta?
We’ve tested the new Image Comparison thoroughly with all kinds of images and sample sets, fixing issues along the way. But nothing beats real-world use. Because this is an entirely new implementation, some things may behave a little differently. We’d love for you to try it in your own workflows and tell us how it performs — what feels great, what doesn’t, and where you hit rough edges.
Your feedback will help us fine-tune everything before the final release.
What’s New
There are two kinds of improvements in Kaleidoscope 6.4: those that come naturally from the new technology, and a few you’ll notice right away.
Performance and Compatibility
Thanks to modern frameworks, Kaleidoscope can now handle larger images — and handle them better. We’ve tested up to 750 megapixels and several hundred megabytes per file. It’s far from instant on a MacBook Pro with an M4 Pro chip — but it works, and that’s impressive.
We’d love to try it on the most powerful Mac out there someday. Until then, let us know if you hit performance limits in your workflows.
Even better, the new Image Comparison finally works inside virtual machines. We’ve missed this capability for years — so if you use VMs for testing or development, this one’s for you.
Image Alignment
Until now, images of different sizes always aligned to the center. Starting with 6.4, you can align by any corner or edge. That means comparing web pages of different lengths or app screenshots with varying dimensions just got a lot easier. See the View menu or the new toolbar button to adjust alignment to your needs.
We’ll have more news in this area soon — stay tuned. For now, we’d love to hear how this new flexibility fits your workflow.
Zoom
We’ve also added a new Zoom to Fit mode that automatically scales your image to fill the window — and keeps doing so until you turn it off. Combined with the existing Adaptive Zoom, this gives you more control and consistency as you resize your window or switch view modes. To top it off, you can now set your default zoom behavior in Settings. Kaleidoscope will remember exactly how you like to work.
In Summary
We hope you’ll enjoy using the new Image Comparison as much as we enjoyed building it. Download the public beta today and put it through its paces — large files, virtual machines, tricky comparisons — whatever your workflow looks like.
If you run into anything unexpected, please let us know. Your feedback will help us make Kaleidoscope even better.
And don’t worry — you can always roll back to the current release if needed.
