In preparation for the upcoming Melodic release, early next week we are planning on uploading OpenCV 3.2 packages for Debian Stretch amd64/arm64 to http://packages.ros.org. This means that any Debian Stretch machines that have packages.ros.org in their /etc/apt/sources.list.d will get
libopencv-* upgraded to 3.2 the next time they run
sudo apt-get upgrade. This will allow maintainers to release a single version of their package that runs across all of the Melodic supported platforms.
Please let us know if you have comments or questions about this change.
Your friendly Melodic maintainers