Generate sized icons for iOS and Watch development using ImageMagick convert

make-icon-sizes.sh

#!/bin/bash

# IMPORTANT: the default options for convert might not give you the
# same quality you will get from Gimp or Photoshop. You might have
# to dig into the convert command line options and tweak them to
# suit what kind of conversion you want. Someday I will do that...
# for now this script is best used for making test icon suites.

# requires ImageMagick for the 'convert' command below.
# http://www.imagemagick.org or on OS X: brew install imagemagick

# Edit the specs list below as needed. Format is points:scale
# This is incomplete... just threw this together and it's missing, for example, iPad sizes.
# Plus see the special case size at the end of the script.
# To add more sizes, just add the points:scale numbers for the size to the specs list here.
export specs="24:2 29:2 29:3 40:2 40:3 44:2 60:2 60:3 86:2 98:2"


export infile=$1

if [[ "$infile" == '' ]]; then
    echo usage: $0 \<input image filename\>
    exit -1
fi

for spec in $specs; do
    echo doing spec $spec
    export points=`echo $spec | cut -f 1 -d':'`;
    export scale=`echo $spec | cut -f 2 -d':'`;
    let "size = $points * $scale"
    convert $infile -geometry ${size}x$size icon-$points\@${scale}x.png
done

# special case
convert $infile -geometry 55x55 icon-27.5\@2x.png