Running ImageMagick on older macOS

We reanimated an old MacBook for the kid so he could download pictures of planes, trains and automobiles, and create his own memory sets (a card game which is apparently called concentration in non-German speaking countries). Turns out the latest macOS running on that particular hardware (10.15 Catalina) does not yet support WebP or AVIF images outside of a browser. No problem, let’s brew ourselves some ImageMagick so we can convert them to PNGs.

Nope. Turns out a dependency (an ingredient?) of that formula, a recent OpenSSL version, assumes as specific Perl dependency is always present. Not on this machine. As some people on the internet recommended against manipulating the system version of Perl, I went with a new homebrewed one and installed the missing IO::Socket::IP via cpan. Still no luck, as installing OpenSSL apparently ignored my new perl version. At some point this was working somehow, but then I stumbled upon the next failing dependency.

I was expecting something similar to npm’s overrides to exist, allowing me to pin an old version of any incompatible dependeny. But based on what I gathered from discussions in Homebrew’s issue tracker, that is not something they want to provide. Which is very unfortunate for my case but totally understandable from an open-source software support point-of-view.

So I gave up and turned to Docker:

FROM debian:latest
RUN apt-get update && apt-get install -y imagemagick
ENTRYPOINT ["magick"]

After building this image with docker build . -t imagemagick, it can be used to convert all .webp and .avif files in the current directory (recursively) to PNG:

for f in $(find . -name '*.webp' -o -name '*.avif'); do
  docker run -v $(pwd):/i imagemagick /i/$f /i/$f.png
done

However, this image has a ridiculous size of 380 MB. So let’s pick a smaller base image:

FROM alpine:latest
RUN apk add --no-cache imagemagick
ENTRYPOINT ["magick"]

While this reduces the size to 33 MB, it has the slight disadvantage of not working:

magick: no decode delegate for this image format `AVIF' @ error/constitute.c/ReadImage/746.
magick: delegate failed `'dwebp' -pam '%i' -o '%o'' @ error/delegate.c/InvokeDelegate/1920.
magick: unable to open file '/tmp/magick-WH2QY7r79RAmEmO-qFYO0Lv219JnOAbk': No such file or directory @ error/constitute.c/ReadImage/785.

So let’s add the missing packages:

FROM alpine:latest
RUN apk add --no-cache imagemagick libwebp libheif
ENTRYPOINT ["magick"]

This increases the built image’s size to 51 MB (~0.5 MB for libwebp and the rest for libheif), but we are still almost 90% below the initial size. 🎉

So as long as Docker runs on macOS Catalina, we are probably safe.