When you go to 0.1 BPP, every codec will look unacceptable, but the current encoder of JPEG XL looks worse than video codecs.
We will likely be able to extend the scale of handling bad quality down to 0.1 to 0.25 BPP, but it definitely has not been a priority since we don't anticipate that users actually would use it for photographs.
(When an image has a low noise level or less features, then we naturally can compress it down to 0.00x BPP with JPEG XL, too. The 0.5 BPP rule of thumb is for normal vacation photographs and selfies :-)
JPEG XL's current encoder is focused on qualities 0.5 BPP and upwards. Current internet image usage averages at 2 to 3 BPP based on Chrome stats from June 2019. See https://www.spiedigitallibrary.org/conference-proceedings-of... Figure 1.
When you go to 0.1 BPP, every codec will look unacceptable, but the current encoder of JPEG XL looks worse than video codecs.
We will likely be able to extend the scale of handling bad quality down to 0.1 to 0.25 BPP, but it definitely has not been a priority since we don't anticipate that users actually would use it for photographs.
(When an image has a low noise level or less features, then we naturally can compress it down to 0.00x BPP with JPEG XL, too. The 0.5 BPP rule of thumb is for normal vacation photographs and selfies :-)