Updated the gist for @_StockLight. As per @jeffbonnes advice at @ticonf melbourne 2013, this version expects a Resources/images directory (instead of Resources/iphone/images) that contains the standard and @2x images which are served straight to iOS and also MDPI Android devices.

images2android.sh

type mogrify >/dev/null 2>&1 || { echo >&2 "» This script requires mogrify. Please install ImageMagick first!"; exit 1; }
 
rm -rf Resources/android/images
mkdir Resources/android/images
mkdir Resources/android/images/res-xhdpi
mkdir Resources/android/images/res-mdpi
 
echo " » Copying the splash screen"
cp Resources/iphone/Default.png Resources/android/images/res-mdpi/default.png
cp Resources/iphone/Default@2x.png Resources/android/images/res-xhdpi/default.png
cd Resources/images
 
echo " » Copying the folder structure so bash won't complain"
find ./* -type d -exec mkdir ../../Resources/android/images/res-mdpi/{} \;
find ./* -type d -exec mkdir ../../Resources/android/images/res-xhdpi/{} \;
 
echo " » Copy all resources to MDPI, this is"
echo "   the same density as a non-retina iOS device"
find ./* -type f -exec cp {} ../../Resources/android/images/res-mdpi/{} \;
cd ../../Resources/android/images/res-mdpi/
 
echo " » Move the retina resources to XHDPI, which"
echo "   has the same density as a retina iOS device"
find ./* -type f -regex ".*@2x.*" -exec mv {} ../res-xhdpi/{} \;
cd ../res-xhdpi
 
echo " » Remove @2x from XHDPI filenames"
find ./* -type f -exec bash -c 'file={}; mv $file ${file/@2x/}' \;
 
cd ../
 
echo " » Generate HDPI by copying XHDPI and resize these by 75%"
mkdir res-hdpi
cp -R res-xhdpi/* res-hdpi
cd res-hdpi
find ./* -type f -exec mogrify -resize 75% {} \;

cd ../

echo " » Generate res-normal-XHDPI by copying XHDPI"
echo "   this seems like it's specific to my project"
mkdir res-normal-xhdpi
cp -R res-xhdpi/* res-normal-xhdpi

echo " » Delete MDPI because android will find these in Resources/images"
rm -rf res-mdpi

echo " » Done!"