Extracting additional channels

[andrey-hider]

What did you do?

Tried to export two alpha channels:

What did you expect to happen?

To be able to get preview of both alpha channels as a png files.

What actually happened?

I've got preview of only one alpha channel:

What are your OS, Python and Pillow versions?

• OS: macOS Monterey 12.1
• Python: 3.9.10
• Pillow: 9.0.0

from PIL import Image

folder = "<path_to_file>"
file = "Alpha Masks Sample with 2 Alphas.tif"
source_file = folder + "/" + file

f = open(source_file, 'rb')
loaded_tif=Image.open(f)
channel_counter = 0
for channel in loaded_tif.split():
    channel_counter += 1
    channel_image = Image.new("L", loaded_tif.size)
    channel_image.paste(channel)
    channel_image.save(folder + '/export_channel'+str(channel_counter)+'.png', optimize=True)
loaded_tif.close()

Archive with example and source code:
pillow_alpha_channels.zip

[radarhere]

What application are the first two screenshots from?

[andrey-hider]

@radarhere
Adobe Photoshop 2022

[radarhere]

If we were to add this functionality, is your image one that we are able to include in our test suite, and distribute under the Pillow license?

[radarhere]

from PIL import Image
with Image.open("Alpha Masks Sample with 2 Alphas.tif") as im:
	print("rawmode", im.tile[0][-1][0])
	print("mode", im.mode)

gives

rawmode RGBXX
mode RGBX

Pillow detects the raw mode as RGBXX and the mode as RGBX.

Pillow is trying to convert the image to a more common format by restricting the number of channels, in opposition to what you're requesting.

[radarhere]

If you've already installed psdtags, then I expect you've also installed the dependency tifffile. In that case, here is a way to solve your problem.

import tifffile
from PIL import Image

folder = "<path_to_file>"
file = "Alpha Masks Sample with 2 Alphas.tif"
source_file = folder + "/" + file

img = tifffile.imread(source_file)
for channel_counter in range(img.shape[2]):
    im = Image.fromarray(img[:, :, channel_counter])
    im.save(folder + "/export_channel"+str(channel_counter+1)+".png", optimize=True)

[andrey-hider]

@radarhere
Thanks for detailed explanation!
Code is working like a charm.
Can I buy you a "virtual beer"? Do you have a Paypal?

[radarhere]

Thanks very much for asking! Ok, for the first time, I've setup a Sponsor button on my profile, so if you'd like to throw some spare change at me, your kindness can express itself there - https:/sponsors/radarhere?frequency=one-time