arm etc2(Ericsson Texture Compression, Unity asset) to png, and png to etc2, use official `etcpack.exe` from [Mali GPU Texture Compression Tool](http://malideveloper.arm.com/resources/tools/mali-gpu-texture-compression-tool/)

etc2_export.py

# -*- coding: utf-8 -*-
"""
Created on Mon Mar 07 00:55:12 2016

@author: Stardrad
"""

import os, struct, fnmatch, time
from PIL import Image

def walk(adr):
    #root,dirs,files = os.walk(adr).next()
    for root,dirs, files in os.walk(adr):
        for name in files:
            if  fnmatch.fnmatch(name, '*.tex') :
                yield os.path.join(root, name)
    
if __name__ == '__main__':
    ntime = time.time()   
    for curName in walk(ur'.'):
        ind = 0
        fName = curName[curName.rindex('\\') + 1:]
        print 'Process %s' % fName
        
        with open(curName,'rb') as fUnityIn:
            print '....',
            fUnityIn.seek(0)
            fNameLen, = struct.unpack('<I', fUnityIn.read(4))
            curPos = fUnityIn.tell()
            curPos += fNameLen
            curPos = (curPos + 4 - 1) / 4 * 4
            fUnityIn.seek(curPos)
            width, height, = struct.unpack('<II', fUnityIn.read(8))
            dataSize, = struct.unpack('<I', fUnityIn.read(4))
            unityType, = struct.unpack('<I', fUnityIn.read(4))
            if unityType != 0x2f :
                print 'Pass type = %08x' % unityType
                continue
            originalPos = fUnityIn.tell()
            fUnityIn.seek(0,2)
            fileSize = fUnityIn.tell()
            fUnityIn.seek(originalPos + 0x4 * 10)
            dataSize_2, = struct.unpack('<I', fUnityIn.read(4))
            tarBpp = float(dataSize * 8) / ( width * height)
            if dataSize_2 == dataSize:
                fUnityIn.seek(originalPos + 0x4 * 10 + 4)
            else:
                fUnityIn.seek(fileSize - dataSize)    
            
            etc2data = fUnityIn.read(dataSize)
            assert len(etc2data) == dataSize
            
        assert width % 4 == 0 and height % 4 == 0
        with open(curName + '.pkm','wb') as fPKMOut:
            fPKMOut.write('PKM ')
            fPKMOut.write('20')  # version
            fPKMOut.write(struct.pack('>H', 3))  # type, 3 = ETC2_RGBA
            fPKMOut.write(struct.pack('>H', width))  # extend_width
            fPKMOut.write(struct.pack('>H', height))  # extend_height
            fPKMOut.write(struct.pack('>H', width))  # width
            fPKMOut.write(struct.pack('>H', height))  # height
            fPKMOut.write(etc2data)
            
        args1 = r'@PATH="D:\Program Files\ARM\Mali Developer Tools\Mali Texture Compression Tool v4.3.0\bin";%PATH'
        args =  'etcpack.exe %s . -ext PNG' % ( curName + '.pkm')
        os.system(args1)
        os.system(args)
        os.remove(curName + '.pkm')
        im1 = Image.open(curName + '.png')
        im1 = im1.transpose(Image.FLIP_TOP_BOTTOM)
        im1.save(curName + '.png');
        print 'save to png'
            
        
    print 'Total time: %lf' % (time.time() - ntime)

etc2_import

# -*- coding: utf-8 -*-
"""
Created on Wed Mar 09 01:48:51 2016

@author: Stardrad
"""

import os, struct, fnmatch, time
from PIL import Image

def walk(adr):
    #root,dirs,files = os.walk(adr).next()
    for root,dirs, files in os.walk(adr):
        for name in files:
            if  fnmatch.fnmatch(name, '*.png') :
                yield os.path.join(root, name)
            
                
if __name__ == '__main__':
    ntime = time.time()   
    for curName in walk(ur'.'):
        ind = 0
        fName = curName[curName.rindex('\\') + 1:]
        print 'Process %s' % fName
        
        print '....',
        
        
        orig_fName = curName[:-4]
        im = Image.open( curName ).convert('RGBA')
        im = im.transpose(Image.FLIP_TOP_BOTTOM)
        png_width,png_height, = im.size
        im.save(curName);
        
        args =  'etcpack.exe %s . -f RGBA' % curName
        
        os.system(args)
        
        with open(orig_fName + '.pkm','rb') as fETC2In:
            fETC2In.seek(0x10)
            etc2Data = fETC2In.read()

        os.remove(orig_fName + '.pkm')
        
        with open(orig_fName,'rb+') as fUnityIn:
            fUnityIn.seek(0)
            fNameLen, = struct.unpack('<I', fUnityIn.read(4))
            curPos = fUnityIn.tell()
            curPos += fNameLen
            curPos = (curPos + 4 - 1) / 4 * 4
            fUnityIn.seek(curPos)
            width, height, = struct.unpack('<II', fUnityIn.read(8))
            if png_width != width or png_height != height:
                print 'Pass , size not match'
                continue
            sizePos = fUnityIn.tell()
            dataSize, = struct.unpack('<I', fUnityIn.read(4))
            unityType, = struct.unpack('<I', fUnityIn.read(4))
            if unityType != 0x2f :
                print 'Pass type = %08x' % unityType
                continue
            originalPos = fUnityIn.tell()
            fUnityIn.seek(0,2)
            fileSize = fUnityIn.tell()
            fUnityIn.seek(originalPos + 0x4 * 10)
            dataSize_2, = struct.unpack('<I', fUnityIn.read(4))
            tarBpp = float(dataSize * 8) / ( width * height)
            if dataSize_2 == dataSize:
                fUnityIn.seek(originalPos + 0x4 * 10 + 4)
            else:
                fUnityIn.seek(fileSize - dataSize)    
            assert len(etc2Data) == dataSize
            fUnityIn.write(etc2Data)
            
            print 'import to %s' % orig_fName

    print 'Total time: %lf' % (time.time() - ntime)