Icon sizes generator for iOS/watchOS/iMessage apps.

icons-generator.sh

#!/bin/bash
# Sizes from https://developer.apple.com/library/ios/#qa/qa1686/_index.html
# Requirements: ImageMagick

function resize {
  GREEN='\033[0;32m'
  BLUE='\033[0;34m'
  DEFAULT='\033[0m'
  echo -e "Generating ${BLUE}$3${DEFAULT} at size ${GREEN}$2 ${DEFAULT}"
  convert $1 -resize $2 $3
}

if [ $1 = '-h' ]; then
  echo "As first param use one of [iphone/ipad/ios/watchos/imessages]"
  echo "keyword, the second param is path to the large image"
  echo ""
  echo "generator iphone 1024.png"
  echo "generator ios 1024.png"
fi

# Icons for iPhone-only Applications
if [ $1 = 'iphone' ]; then
  resize $2 512x512    iTunesArtwork.png     # App list in iTunes
  resize $2 1024x1024  [email protected]  # App list in iTunes on devices with retina display
  resize $2 120x120    [email protected]        # Home screen on iPhone/iPod Touch with retina display
  resize $2 180x180    [email protected]        # Home screen on iPhone with retina HD display
  resize $2 76x76      Icon-76.png           # Home screen on iPad
  resize $2 152x152    [email protected]        # Home screen on iPad with retina display
  resize $2 167x167    [email protected]      # Home screen on iPad Pro
  resize $2 40x40      Icon-Small-40.png     # Spotlight
  resize $2 80x80      [email protected]  # Spotlight on devices with retina display
  resize $2 120x120    [email protected]  # Spotlight on devices with retina HD display
  resize $2 29x29      Icon-Small.png        # Settings
  resize $2 58x58      [email protected]     # Settings on devices with retina display
  resize $2 87x87      [email protected]     # Settings on devices with retina HD display
  
  # Apple does not list these sizes
  resize $2 40x40      [email protected]  # iPhone notification iOS 7-11 on devices with retina display
  resize $2 60x60      [email protected]  # iPhone notification iOS 7-11 on devices with retina HD display
fi

# Icons for iPad-only Applications
if [ $1 = 'ipad' ]; then
  resize $2 512x512    iTunesArtwork.png     # Ad Hoc iTunes
  resize $2 1024x1024  [email protected]  # Ad Hoc iTunes on devices with retina display
  resize $2 76x76      Icon-76.png           # Home screen on iPad
  resize $2 152x152    [email protected]        # Home screen on iPad with retina display
  resize $2 167x167    [email protected]      # Home screen on iPad Pro
  resize $2 40x40      Icon-Small-40.png     # Spotlight
  resize $2 80x80      [email protected]  # Spotlight on devices with retina display
  resize $2 29x29      Icon-Small.png        # Settings
  resize $2 58x58      [email protected]     # Settings on devices with retina display
  
  # Apple does not list these sizes
  resize $2 20x20      Icon-Small-20.png     # iPad notification iOS 7-11
  resize $2 40x40      [email protected]  # iPad notification iOS 7-11 on devices with retina display
fi

# Icons for Universal Applications
if [ $1 = 'ios' ]; then
  resize $2 512x512    iTunesArtwork.png     # App list in iTunes
  resize $2 1024x1024  [email protected]  # App list in iTunes for devices with retina display
  resize $2 120x120    [email protected]        # Home screen on iPhone/iPod Touch with retina display
  resize $2 180x180    [email protected]        # Home screen on iPhone with retina HD display
  resize $2 76x76      Icon-76.png           # Home screen on iPad
  resize $2 152x152    [email protected]        # Home screen on iPad with retina display
  resize $2 167x167    [email protected]      # Home screen on iPad Pro
  resize $2 40x40      Icon-Small-40.png     # Spotlight
  resize $2 80x80      [email protected]  # Spotlight on devices with retina display
  resize $2 120x120    [email protected]  # Spotlight on devices with retina HD display
  resize $2 29x29      Icon-Small.png        # Settings
  resize $2 58x58      [email protected]     # Settings on devices with retina display
  resize $2 87x87      [email protected]     # Settings on devices with retina HD display
  
  # Apple does not list these sizes
  resize $2 20x20      Icon-Small-20.png     # iPad notification iOS 7-11
  resize $2 40x40      [email protected]  # iPhone/iPad notification iOS 7-11 on devices with retina display
  resize $2 60x60      [email protected]  # iPhone notification iOS 7-11 on devices with retina HD display
  
fi

# Icons for Watch Applications
if [ $1 = 'watchos' ]; then
  resize $2 80x80      [email protected]   # Home screen on Apple Watch (38mm/42mm), Long-Look notification on Apple Watch (38mm)
  resize $2 88x88      [email protected]   # Long-Look notification on Apple Watch (42mm)
  resize $2 172x172    [email protected]   # Short-Look notification on Apple Watch (38mm)
  resize $2 196x196    [email protected]   # Short-Look notification on Apple Watch (42mm)
  resize $2 48x48      [email protected]   # Notification center on Apple Watch (38mm)
  resize $2 55x55      [email protected] # Notification center on Apple Watch (42mm)
  resize $2 58x58      [email protected]   # Settings in the Apple Watch companion app on iPhone
  resize $2 87x87      [email protected]   # Settings in the Apple Watch companion app on iPhone 6 Plus
fi

# Icons for iMessage Extensions
if [ $1 = 'imessage' ]; then
  resize $2 1024x768   Messages1024x768.png  # Messages App Store
  resize $2 120x90     [email protected]  # Messages app drawer on iPhone/iPod Touch with retina display
  resize $2 180x135    [email protected]  # Messages app drawer on iPhone with retina HD display
  resize $2 134x100    [email protected]  # Messages app drawer on iPad with retina display
  resize $2 148x110    [email protected]  # Messages app drawer on iPad Pro
  resize $2 54x40      [email protected]  # Breadcrumb icons in the chat transcript on devices with retina display.
  resize $2 81x60      [email protected]  # Breadcrumb icons in the chat transcript on iPhone with retina HD display
  resize $2 64x48      [email protected]  # Messages app management screen, message bubble branding on devices with retina display
  resize $2 96x72      [email protected]  # Messages app management screen, message bubble branding on iPhone with retina HD display
fi

I don't have ImageMagick, so I replaced it with sips:

res=`echo $2 | cut -dx -f1`
#convert $1 -resize $2 $3
sips -Z $res --out "$3" "$1"