Using MozJPEG via Docker

mozjpeg , a jpeg encoder project from mozilla, is a fantastic way to optimize your jpeg files . setting it up however might be quite a hassle. fortunately, a virtualized environment such as docker offers a much simplified way to use mozjpeg.

the important requirement is that you have docker installed and ready to use. if you are on linux, this should be easy. for os x and windows users, follow the steps in my previous blog post on easy docker on os x .

first, we will grab mozjpeg source code :

git clone git://github.com/mozilla/mozjpeg.git 
cd mozjpeg 
git checkout v3.1

in the current directory, create a dockerfile with the following content. as you can see, here we will base it on alpine linux since it is quite small (around 5 mb).

from alpine:3.3 
add . /source 
run apk --update add autoconf automake build-base libtool nasm 
run cd /source && autoreconf -fiv && ./configure --prefix=/usr && make install

once this dockerfile is ready, fire it up with:

docker build -t mozjpeg .

you can watch the progress as docker grabs alpine 3.3 base image and let alpine’s package manager, apk , install a number of dependent packages. after that, mozjpeg is being compiled and built from source. once this is completed (it may take a while), we are ready to utilize this new image for optimizing jpegs. also, there is no need to stay in the current directory.

for the basics on using mozjpeg, i recommend reading the article using mozjpeg to create efficient jpegs . let’s say we have a picture we want to optimize, e.g. photo.jpg . we can start a new docker container containing the above compiled mozjpeg and use it as follows:

cd ~/documents 
docker run -v $pwd:/img mozjpeg sh -c "/opt/mozjpeg/bin/cjpeg -quality 80
  /img/photo.jpg > /img/photo_small.jpg"

the command-line option –v $pwd:/img maps the current directory on your host machine to /img as seen from within the container. after that, a shell is invoked with the full command to start mozjpeg’s cjpeg at quality level 80. when i tried this on a simple photo, i was very happy with the optimized version while i got a massive decrease in file size (from 158 kb to 45 kb). of course, your mileage may vary and make sure you read kornel’s excellent article on fair image comparison .

still not optimizing your jpeg files? now you have no more excuse!