FFMpeg next will likely support AVIF and HEIC/HEIF

[Zebulon84]

I have done some quick tests for one specific application : compress scans of various administrative documents (e.g. invoices), so quite low quality needed compared to what most people here may wish for, and that's not photos. Small color changes are not a problem, the criteria is only no big artifacts.
The best was AVIF (@40%), second Jpeg XL, then HEIF, WebP and JPG. I haven't kept the test files, but IIRC, AVIF was about 20% smaller than JXL, and quicker to encode. I did not do decode tests as I rarely need to open several documents in a row, and opening one is pretty quick (~1s on my i3-12100).
I used Skanlite (from KDE), I don't know precisely which encoder is used.

Of course, the results may be quite different for high quality photo encodings, screenshots...

[Z2697]

As a matter of fact, HEIF is just a container. The quality and speed is highly dependent on the encoder used, whether it's the HEVC variant (HEIC), AV1 variant (AVIF) or else.

Especially for these Video Codec Based variants, there are more choices and bigger differences than you typically get for image encoders (within same codec).

(WebP is also video codec (VP8) based but you don't have encoders to choose though, also the only supported pixel format is YUV(A)420P8, meh.)



Now the general situation is aomenc and svt-av1 struggles to match the quality of a tuned x265 in mid to high bitrate, for Intra only images, there's less encoding tool they can use, and the "advantage" of AV1 side is even less.

But AV1 might have more widely supported (decoding side) "SCC extensions", that could be a potential benefit but I don't think it's significant for anything not screen content.

My personal ranking is HEIC (x265) > JPEG XL (libjxl) > AVIF (aomenc or svt-av1) for lossy encoding. (WebP is excluded because it sucks, or somewhere at the bottom not even able to compete with JPEG because the lack of 4:4:4 support)

(By sucks I mean I always considered the VP series is half a generation off compared to MPEG series like VP9 is between AVC and HEVC, so that means VP8 is... similar to or less than AVC?)



Now if we need to talk about lossless encoding, well... WebP wins (kind of). (Assuming your input is RGB! If your input is YUV things might get more interesting but I didn't test that.)

Now the VCB formats or HEIF variants sucks because of the lack of specifically designed lossless mode.

JPEG XL is basically two parts (VarDCT for lossy and Modular for lossless) merged together and somtimes cooperating perhaps, WebP actually has a secret sauce called VP8L but only supports ARGB (32bpp / 8bpc) even for no-alpha images. (Despite the similarity of the name to VP8, it's actually better than just a quantization bypass or something like in HEVC or AV1 lossless, in terms of compression ratio, I didn't take a deeper look)

My personal ranking is JPEG XL (libjxl) > WebP > PNG > [VCB HEIF variants, you name it] for lossless encoding.

Be careful that some VCB HEIF encoding tools might be in fact not really lossless and give you illusions that they performed well in lossless tasks. (Like some early versions of a certain library that I'm not sure if it's libheif or not, they convert RGB pixels to YUV first.)



One step further, animations.

Video codec based formats wins again. Even in lossless mode. When compressing single image they are not as powerful, they are better at exploiting inter-frame compressions thus makes up for the shortcomming. (But your animations will need to have enough frames to make the benefits significant enough, or even get to outweight the shortcoming)
Other formats previously mentioned are basically "ranked" like in the single frame "ranks".

(DISHORNORABLE mention: WebP, while being VP8, a video codec based, seemingly not taking the advantage of better inter-frame compression. And VP8 is very old.)