Drawing text on image works incorrectly if the image opacity is 0

[victor-radivchev]

What did you do?

Wanted to draw text on an image with 0 opacity

What did you expect to happen?

RGB channels to have changed values only for the pixels of the letters:

What actually happened?

The channels changed for the entire bounding box of the text:

Also if opacity for the image is >= 1, the font is ImageFont.load_default().font or the version of Pillow is 6.2.2, then I get the expected behavior.

What are your OS, Python and Pillow versions?

• OS: Ubuntu 18.04.5 LTS / MacOS 10.15.7
• Python: 3.7.8
• Pillow: 8.2.0

from PIL import Image, ImageDraw, ImageFont

font = ImageFont.truetype("Pillow/Tests/fonts/FreeMono.ttf", 40)
text = 'TEXT'
text_im = Image.new('RGBA', (100, 50), (255, 255, 255, 0))
draw = ImageDraw.Draw(text_im)
draw.text((0, 0), text, fill=(0, 0, 0), font=font)
r, g, b, _ = text_im.split()

[radarhere]

I'm not able to replicate this on my machine. I also get the expected result on our CIs - AppVeyor and GitHub Actions (Windows, our Docker images and Linux and macOS)

I don't really have any ideas about why your machines are different. How did you install Pillow? What version of FreeType are you using?

>>> from PIL import _imagingft
>>> _imagingft.freetype2_version
'2.10.4'

[victor-radivchev]

This is the image that the Pillow 8 generates (this one is the same as "Tests/images/5431.png"):

And this is the one that Pillow 6 generates (this one is different from "Tests/images/5431.png"):

They look to be the same, but they aren't:

>>> text_im_6.tobytes() == text_im_8.tobytes()
False

The difference becomes visible if I either split them by channels or convert them to grayscale:

text_im_8.convert('L')

text_im_6.convert('L')

[radarhere]

Thanks for the explanation. Testing, this is the result of #4566.

Testing, it only happens when the opacity is 0. For even an opacity of 1, it is fine. If you'll allow me to ask - why is it a problem that the RGB values change? My inclination is to think that if the opacity is 0, it doesn't matter what color the pixels are.

[victor-radivchev]

As long as the image stays in RGBA there is no problem, but if it ever gets converted to RGB or L, then it becomes an issue. That's how I stumbled upon it - my script was ending with a grayscale image as a result.

[radarhere]

I've created PR #5434 to resolve this.