HEIC encoding buggy

[nji9]

First of all the heic format seems not capable to true lossless encoding.
I tried to find out, but not being a prof on that I wasn't successful.
However my "reference" for graphic is GIMP, and in its export dialog
for heic it says "(nearly) lossless".
(BTW This expression seems rather sensless to me,
as the saying "a miss is as good as a mile" says,
if just one bit is different than you shouldn't use the word lossless at all.
"Nearly lossless" makes no sense).
Maybe you check the format's properties?
And then change to "nearly lossless" too, or better leave it completely.
But that's only the minor thing.

The big bug with xnviewmp's heic encoding is that the encoding quality
doesn't match the option slider's setting.
If you use the max value (100 (= "lossless") and compare that to the
heic file that GIMP produces with its max value,
you see that xnview's file size is much smaller than GIMP's
and that the resulting quality is very poor compared to GIMP's.
This means that your encoder is very poor even with its max settings,
or that there is a bug in using the encoder.
If you can't help that, the best thing would be to do something
like a "half slider" (max value = "50"), and tag 50 as "still not good"
or something like that.
To my opinion.

I attach the two arithmetical differences from the original 24bit image
to a heic file encoded by XnViewMP and a heic file encoded by GIMP.
If you split the files to HSV channels you see the BIG difference.

[xnview]

could you send me original and output?

[nji9]

Sorry, attchment size limit doesn't allow.
It was just to demonstrate anyway.
Why don't you use an arbitrary file by yourself?

[xnview]

you can send them by mail

[xnview]

Thanks to your detailed description I can reproduce the problem.

[nji9]

Glad I could help.

However I'm surprised by the classification of it as "minor" bug.
(Was it a "minor" effort for you to kill that bug?)

All the users that trusted on the lossless encoding of heic and jxl
viewtopic.php?p=180706#p180706
have lost their originals now, even without knowing about it.
That's severe I might think.

[xnview]

i don't use classification...

[nji9]

But in
https://www.xnview.com/mantisbt/view.php?id=2445
it says so (?)

[xnview]

This problem is supposed to be fixed in XnView MP 1.3.1. Please check and confirm the bug fix here.