Better compression for PNGs please!

I would appreciate more options (basically, much smaller files) for PNG export.

At the moment my limited testing agrees with this closed thread that Squash’s PNG export creates larger files than the originals. I hope this can be fixed.

I don’t know anything about PNG algorithms, so I have no idea what performance you’d expect from Crush and Zopfli, as used by Squash. But I do know that a utility called ImageAlpha can shrink web PNGs by 80–90% by allowing you to choose the number of colour levels. ImageAlpha uses the pngquant and pngnq algorithms, if that makes any difference.

If you could match that performance for PNG it would be wonderful. I guess WebP is the way ahead, but I have a lot of users on old versions of Safari so I’m not ready for WebP quite yet.

I’ve received no answer from Realmac to my question. A compression app that increases the size of a file makes no sense, it should at the very least leave it as it was (in terms of compression) and just process the rest of the options. I haven’t used Squash since and plan not to use it until this is resolved or addressed.


If you compress a jpg that has already been compressed you probably won’t see any reduction in file size, in fact, the file may ever be bigger. If you compress a high-quality original image with very little compression, you’re going to see great savings. This is when Squash really shines.

As Squash does more than just compress, it can resize, convert formats, apply filters, watermark, etc, we leave it to the user to compare the input and output file sizes. We do offer a little warning if the file gets bigger though…

Screenshot 2021-12-20 at 9.10.52 pm

Hope that makes sense.

@realmac, thanks – we certainly do appreciate Squash’s ease of use and other fine features. But note that Denis and I are talking about PNG files, not JPGs. I for one don’t understand how PNG works, but the fact that you offer two different algorithms suggests that you do aim to provide some degree of shrinking, and that’s not happening for us. My test file is a standard macOS screenshot, so it hasn’t been through any fancy processing before I open it in Squash.

As I said above, I’ve seen lossy PNG in action (by restricting the colour palette) and it works very well. If you could provide something like this in the future we would appreciate it. If that’s not the plan, please let us know.

As Charles mentions, we’re talking about png. In the closed thread I had this picture, showing a png file that is 828 KB before being processed by Squash and it’s 2.7 MB after. The before/after are the same dimensions and the only option is to retain dates.

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Ah yes, sorry, that makes much more sense. Will look into it.

Thanks @realmac!

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