Use the GraphicsMagick (1.3.30) inside Heroku. Works with heroku-18.
Requires heroku-buildpack-apt
Insert these buildpacks before the main buildpack for your application:
Make sure the apt buildpack is included before this buildpack.
heroku buildpacks:add --index 1 https://github.com/heroku/heroku-buildpack-apt
heroku buildpacks:add --index 2 https://github.com/bogini/heroku-buildpack-graphicsmagick
Include these at the beginning of your Aptfile
debhelper
g++
gsfonts
libbz2-dev
libexif-dev
libfreetype6-dev
libice-dev
libjbig-dev
libjpeg-dev
liblcms2-dev
libltdl-dev
libpng-dev
libsm-dev
libtiff-dev
libwebp-dev
libwmf-dev
libx11-dev
libxext-dev
libxml2-dev
perl
sharutils
transfig
x11proto-core-dev
zlib1g-dev
The next time you push your application it should install graphicsmagick before your application buildpack.
For more info see Using multiple buildpacks for an app