XnView Software

Nice! Should have spotted that myself.

Just for my understanding. Why may be the Xnview file bigger?
Here is what i mean. The Xnview file is 200kB bigger but the pure picture data must be the same
since jpegtran creates identical files out of out_cjpegli.jpg and out_Xnview.jpg

original.jpg 100% = 4.314.392 Bytes

cjpegli original.jpg ...

Yeah, guetzli relies mainly on butteraugli. Jpegli also to some degree. So in some areas the results are similar but with guetzli other areas get blocky where with jpegli it doesn't.
Jpegli seems pretty mature.

I doubt you miss much.
I personaly was surprised when guetzli was new about the idea behind. Unfortunately guetzli sometimes creates blocks and borders that doesn't belong there so i stopped using it.
When i remember right these issues were reported to the devs but not fixed after release because ...

After the plugin installed i restarted XnView MP x64 and then there is "JPG Guetzli JPEG" as option under Save As.

Guetzli can't do anything but 1x1,1x1,1x1. If the ouput is different it isn't a guetzli file.

When we are at it.
Saving a jpg file as "JPG - Guetzli" in XnView MP uses the long time the guetzli encoder needs but saves a different file. Guetzli has always sub-sampling 1x1,1x1,1x1 but when i just tried it creates a sub-sampling 2x2,1x1,1x1 file with the size of the default jpg encoder.

In libjxl v0.10.2 is a cjpegli.exe that produces 100% valid jpg files.
https://github.com/libjxl/libjxl/releases/tag/v0.10.2
The only reason why the produced files may be incompatible is it creates progressive files by default.
Already a year back at an early stage jpegli tested very well and now ...

There is a new king in town!
jpegli does really well and shows jpeg ain't dead yet. It is fast also.
https://github.com/libjxl/libjxl/tree/main/lib/jpegli

Visual comparisons imho show jpegli more robust and efficient as guetzli and miles ahead of mozjpeg quality.

Unfortunately Xnview/imagemagick ...

The first start of MP takes 3 seconds once a day since i use Win 11. After that it starts immediately. On Win 10 it was fine.

It may be worth to add the latest Guetzli from Git. It works better here with files that had no good compression before maybe because of code optimizing and a new Butteraugli.

Interesting that this was it. It shouldn't crash ending the process with simply hitting ESC imho.
I'd suggest to not use guetzli at this point. It seems to reduce quality to much when used in MP.
Have a look here: https://newsgroup.xnview.com/viewtopic.php?f=62&t=36099#p144737
I suggest some extra ...

It may simply not done with processing. guetzli needs lots of processing time. 2-3 minutes is normal even for small 2 megapixel pics here with a 4.4GHz machine.

To my suggestion above i saw guetzli itself will add an "--preserve-exif" option. https://github.com/google/guetzli/pull/175