XnView Software

AFAIK that's expected, because AVIF isn't actually 100% lossless per definition; only visually. Simply because there's always a YUV <-> RGB conversion happening when you open/save an image.

It's only lossless in the sense that, if you open an AVIF file, change only part of it and then save it ...

I only tried with 24-Bit images (with Alpha Channel). I.e. the example I attached previously.

Some other formats work fine, i.e. PNG to PNG does not alter.

Also the same for conversion to .WEBP (I encountered).

For AVIF/HEIC, it's perhaps due to color space conversion...



Look at the Comparison preview image, at the section that should be 100 percent transparent. Note that the image indicated that different part of the transparency are ...

The problem also happens when going from PNG to WEBP [LossLESS]. In WebP There are changes (not True LossLESS).

Also the same for conversion to .WEBP (I encountered).

And maybe more formats ? (I have not checked them all). Maybe you can do some through checking.

When I convert a .PNG file (with an Alpha Channel), to AVIF [LossLESS] format, and then re-compared the result Pixel by Pixel (using software techniques), the AVIF [LossLESS] format alters the parts of the image. Change is Not visually perceivable.

To make SURE, double check: I converted the ...