Tool to batch convert android resource bitmaps to different densities

Here is a simple script to create lower-resolution Android drawables from higher-resolution ones.

For example, given a batch of -xhdpi images, it can generate -hdpi and -mdpi images.

With this script, it’s possible to export only highest-resolution artwork from authoring tools and then create the lower-resolution versions with a few batch commands.

Script usage:

drawable_convert.py -d res/drawable-mdpi -d res/drawable-hdpi res/drawable-xhdpi-v14/*.png

This will take every png file from xhdpi and place lower-resolution versions into mdpi and hdpi folders.

http://kmansoft.com/2012/05/23/scale-android-drawables-with-a-script/
original script, https://gist.github.com/2771791

---

Script itself, to avoid dependency on github gist/original blogpost.
name drawable_convert.py

#!/usr/bin/python

import sys
import argparse
import os
import re

'''
A simple script to create lower-resolution Android drawables from higher-resolution ones.

For example, given a batch of -xhdpi images, you can generate -hdpi and -mdpi images.

This makes it possible to only export highest-resolution artwork from image authoring tools, and
automate the rest.

Usage:

   drawable_convert.py -d res/drawable-mdpi -d res/drawable-hdpi res/drawable-xhdpi-v14/select*.png

   ... will take select*.png from xhdpi and place versions into mdpi and hdpi folders.

   Correct resize ratios are computed based on resource directory names.

   Actual scaling is done by ImageMagick's convert command.
'''

class Converter:
    def __init__(self, dstList):
        print u'Dst list: {0}'.format(dstList)
        self.mDstList = dstList

    def convert(self, src):
        for dstpath in self.mDstList:
            (srcpath, srcname) = os.path.split(src)
            dst = os.path.join(dstpath, srcname)
            self.convertOne(src, dst)

    def convertOne(self, src, dst):
        print u'\n*****\n{0} to {1}\n*****\n'.format(src, dst)
        '''
        Determine relative density
        '''
        srcDpi = self.getDpi(src)
        dstDpi = self.getDpi(dst)

        if srcDpi < dstDpi:
            print u'NOT converting from {0}dpi to {1}dpi'.format(srcDpi, dstDpi)
        else:
            factor = dstDpi*100/srcDpi
            print u'Converting from {0}dpi to {1}dpi, {2}%'.format(srcDpi, dstDpi, factor)
            cmd = u'convert -verbose "{0}" -resize "{2}%x{2}%" "{1}"'.format(src, dst, factor)
            os.system(cmd)

    def getDpi(self, f):
        p = os.path.dirname(f)
        if re.match('.*drawable.*\\-mdpi.*', p):
            return 160
        elif re.match('.*drawable.*\\-hdpi.*', p):
            return 240
        elif re.match('.*drawable.*\\-xhdpi.*', p):
            return 320
        else:
            raise ValueError(u'Cannot determine densitiy for {0}'.format(p))

if __name__ == "__main__":
    '''
    Parse command line arguments
    '''
    parser = argparse.ArgumentParser(description='Converts drawable resources in Android applications')
    parser.add_argument('-d', dest='DST', action='append', required=True, help='destination directory')
    parser.add_argument('src', nargs='+', help='files to convert (one or more)')
    args = parser.parse_args()

    cv = Converter(args.DST)
    for src in args.src:
        cv.convert(src)


'''


if [ $# -lt 1 ] ; then
    echo "Usage: $0 file_list"
    exit 1
fi

for f in $*
do
    echo "File: ${f}"
    convert -verbose "${f}" -resize "75%x75%" "../drawable-hdpi/${f}"
    convert -verbose "${f}" -resize "50%x50%" "../drawable-mdpi/${f}"
done

'''

Final-Android-Resizer did the job for me and was simple to use but had all the options I needed: https://github.com/asystat/Final-Android-Resizer

Android Asset Studio may be helpful, although it is not exactly what you asked for.