from PIL import Image

class RGBAPacker(object):
    def process(self, output_file, inputs=None):
    	# -- we assume "inputs" is a dictionary of image files, with the keys corresponding to the channels they want packing in.
    	inputs = inputs or dict()
    	r = Image.open(inputs.get('r')).convert('L')
        g = Image.open(inputs.get('g')).convert('L')
        b = Image.open(inputs.get('b')).convert('L')
        a = Image.open(inputs.get('a')).convert('L')
        
        output = Image.merge('RGBA', r, g, b, a)
        output.save(output_file)