Closed
Description
Hi, recently messed with PIL to encounter what is probably a bug
What did you do?
import numpy as np
from PIL import Image
# Source of data for image
im_data: np.typing.NDArray = np.array([[255]], dtype=np.uint8)
assert im_data[0, 0] == 255 # OK
# Attach to buffer protocol of an array, should reflect changes in im_data
im: Image.Image = Image.frombuffer(mode="L", size=(1, 1), data=im_data)
assert im_data[0, 0] == 255 # OK
assert im.getdata()[0] == 255 # OK
im_data[:, :] = np.array([[128]], dtype=np.uint8)
assert im_data[0, 0] == 128 # OK
assert im.getdata()[0] == 128 # OK!
im.save("./test_image.bmp")
assert im_data[0, 0] == 128 # OK
assert im.getdata()[0] == 128 # OK
im_data[:, :] = np.array([[64]], dtype=np.uint8)
assert im_data[0, 0] == 64 # OK
assert im.getdata()[0] == 64 # Failed!!! It is still == 128What did you expect to happen?
Line with last assert should pass the assertion:
...
assert im.getdata()[0] == 64 # Should pass
What actually happened?
Yes, so it seams that Image.save() messes with image buffer state. Moreover, this is actually explicitly stated that it does in source code:
Line 2513 in af09976
# def save(...):
# ...
# may mutate self!
self._ensure_mutable()Once one saved the image, one can no longer work with buffer and expect image working properly.
I can try to work out some patches but really I am somewhat new to the pillow and not well aware of all internal connections with things. It would be nice to have some hints on what may going on - then I can try to fix this.
What are your OS, Python and Pillow versions?
OS:
lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 22.04.5 LTS
Release: 22.04
Codename: jammyPython:
Python 3.12.9- Prebuilt binary from deadsnakes ppa if I remember correctly
Pillow:
poetry run python3 -m PIL --report
--------------------------------------------------------------------
Pillow 11.1.0
Python 3.12.9 (main, Feb 5 2025, 08:49:00) [GCC 11.4.0]
--------------------------------------------------------------------
Python executable is [...]/.venv/bin/python3
Environment Python files loaded from [...]/.venv
System Python files loaded from /usr
--------------------------------------------------------------------
Python Pillow modules loaded from [...]/.venv/lib/python3.12/site-packages/PIL
Binary Pillow modules loaded from [...]/.venv/lib/python3.12/site-packages/PIL
--------------------------------------------------------------------
--- PIL CORE support ok, compiled for 11.1.0
*** TKINTER support not installed
--- FREETYPE2 support ok, loaded 2.13.2
--- LITTLECMS2 support ok, loaded 2.16
--- WEBP support ok, loaded 1.5.0
--- JPEG support ok, compiled for libjpeg-turbo 3.1.0
--- OPENJPEG (JPEG2000) support ok, loaded 2.5.3
--- ZLIB (PNG/ZIP) support ok, loaded 1.2.11, compiled for zlib-ng 2.2.2
--- LIBTIFF support ok, loaded 4.6.0
--- RAQM (Bidirectional Text) support ok, loaded 0.10.1, fribidi 1.0.8, harfbuzz 10.1.0
*** LIBIMAGEQUANT (Quantization method) support not installed
--- XCB (X protocol) support ok
--------------------------------------------------------------------