Premultiply-Alpha-in-Folder

Make sure you have backup of the folder, since this tool rewrites all the images!

Python script that recursively premultiplies rgb values by alpha for all .png images in a folder, i.e.:

pixel_in = (r,g,b,a)
pixel_out = (r * a, g * a, b * a)

Installing dependencies

You need python and pip installed. Then just run

sudo pip install Pillow 

Usage

$python Premultiply.py images

where images is the root folder, with subfolder

$python Premultiply.py 'images folder'

Use apostropes if the folder name contains spaces