Script to convert image files to the Slack suggest format: 128x128 PNG with transparent background.

emojify

#!/bin/zsh
# this requires imagemagick to run
# brew install imagemagick && brew install ghostscript

# on Mac, download then run `mv ~/Downloads/emojify /user/local/bin/emojify`

# emojify file [output-name]
# examples
# emojify ~/Downloads/img.png winky-face
# emojify ~/Downloads/winky-face.jpg
# emojify ~/Downloads/winky-face.png (this will overwrite, since it's a PNG)


if [[ "${2}" != "" ]]
then 
  output="${1:h}/${2}".png
else
  output="$1:r".png
fi
convert -background none -gravity center $1 -resize 128x128 -extent 128x128 $output