extracts high-resolution emoji pngs from /System/Library/Fonts/Apple Color Emoji.ttf (OS X 10.11) or /System/Library/Fonts/Apple Color Emoji.ttc (macOS 10.12)
$ ruby emoji_extractor.rb
$ ls images
20x20 32x32 40x40 48x48 64x64 96x96 160x160
$ file images/160x160/1.png
images/160x160/1.png: PNG image data, 160 x 160, 8-bit/color RGBA, non-interlaced