Convert png images to lossy avif - imagemagick

Question

I try to compress my ~1MB pngs to get a smaller image.
When I compress my images to jpeg with:
for i in card*.png ; do convert -resize 445x625 -background white -flatten "$i" ../medium/"${i%.*}.jpg" ; done
they end up about 100kb
So I tried
for i in card*.png ; do echo $i; convert -resize 445x625 "$i" ../medium/"${i%.*}.avif" ; done
which results in avif images ~400kb, I guess because they are losslessly compressed.
How do I create lossy compressed avif images? And what would be a useful quality level to get images with the text still clearly readeable?
(I use ImageMagick 6.9.10-23 on Ubuntu)

Answer 1

libheif
You can install
apt install libheif-examples
and then use heif-enc to create heif files with:
for i in card*.png ; do echo $i; heif-enc "$i" -o "${i%.*}.avif" ; done
If you need avif format, you need to compile the latest version of libheif, which has the -A option to create avif files.
(There is a section in the README there how to build it on your system. But at least on Ubuntu this is not leading to a running heif-enc)
Better use avifenc:
# Install Homebrew
/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
sudo apt install zsh # needed for this pspecific package install
brew install joedrago/repo/avifenc
Now you have the tool to create avif files with the syntax:
avifenc [options] input.[jpg|jpeg|png|y4m] output.avif
(use avifenc --speed 4 --min 20 --max 22 -j 8 to get a higher compression and use all 8 cores)