Scale images with PIL preserving transparency and color?

Question

Say you want to scale a transparent image but do not yet know the color(s) of the background you will composite it onto later. Unfortunately PIL seems to incorporate the color v

Answer 1

You can resample each band individually:

im.load()
bands = im.split()
bands = [b.resize(size, Image.LINEAR) for b in bands]
im = Image.merge('RGBA', bands)

EDIT

Maybe by avoiding high transparency values like so (need numpy)

import numpy as np

# ...

im.load()
bands = list(im.split())
a = np.asarray(bands[-1])
a.flags.writeable = True
a[a != 0] = 1
bands[-1] = Image.fromarray(a)
bands = [b.resize(size, Image.LINEAR) for b in bands]
a = np.asarray(bands[-1])
a.flags.writeable = True
a[a != 0] = 255
bands[-1] = Image.fromarray(a)
im = Image.merge('RGBA', bands)