Mac OS X 10.13.4+: Convert any image to HEIF/HEIC format
Usage: HEIF [-q=quality] <image>
where quality is in range from 0.1 (max compression) to 1.0 (lossless), default is 0.76
Compiling on macOS (to create executable HEIF and copying to bin folder):
cd HEIF
swiftc -o HEIF main.swift
cp HEIF /usr/local/bin
Or simply run from terminal without compilation:
./main.swift <image>
Please note: odd image dimensions will be truncated by Apple's codec to even ones.