Different pixel value when opening same slide on Linux and Windows

[loic-lb]

Context

Issue type (bug report or feature request): Different pixel value when opening same slide on Linux and Windows
Operating system (e.g. Fedora 24, Mac OS 10.11, Windows 10): Ubuntu 20.04.4 LTS, Windows 10
Platform (e.g. 64-bit x86, 32-bit ARM):
OpenSlide Python version (openslide.__version__): 1.2.0 (on both OS)
OpenSlide version (openslide.__library_version__): 3.4.1 (on both OS)
Slide format (e.g. SVS, NDPI, MRXS): NDPI

Details

Dear all,

When trying to read a slide from Warwick HER2 dataset in a single array at level 5, I get different values depending I am using openslide on Windows or Linux. Both versions of openslide python are the same as the openslide library version. The offset value is relatively small since it seems to differ by only one unit (cf tables on the left of the screenshots I joined). However, this difference is enough to impact my processing afterward. You can also notice on the screenshots I joined that, for instance, you get something significantly different when summing the value of pixels.

Thank you for your help,

Linux capture:

Windows capture:

[bgilbert]

OpenSlide shouldn't be doing anything different on different platforms. It's possible that there's a behavior difference in the underlying image libraries. I'd recommend comparing the versions of the JPEG library (either libjpeg or libjpeg-turbo), pixman, cairo, and possibly Pillow. You might try reducing divergence by comparing the latest OpenSlide Windows build with Ubuntu 22.04 or Fedora 36.