How to use PIL to make all white pixels transparent?

Solution 1:

You need to make the following changes:

• append a tuple (255, 255, 255, 0) and not a list [255, 255, 255, 0]
• use img.putdata(newData)

This is the working code:

from PIL import Image

img = Image.open('img.png')
img = img.convert("RGBA")
datas = img.getdata()

newData = []
for item in datas:
    if item[0] == 255 and item[1] == 255 and item[2] == 255:
        newData.append((255, 255, 255, 0))
    else:
        newData.append(item)

img.putdata(newData)
img.save("img2.png", "PNG")

Solution 2:

You can also use pixel access mode to modify the image in-place:

from PIL import Image

img = Image.open('img.png')
img = img.convert("RGBA")

pixdata = img.load()

width, height = img.size
for y in range(height):
    for x in range(width):
        if pixdata[x, y] == (255, 255, 255, 255):
            pixdata[x, y] = (255, 255, 255, 0)

img.save("img2.png", "PNG")

You can probably also wrap the above into a script if you use it often.