image artifacts in slide.read_region at higher levels

[PerloDaniele]

Context

Issue type (bug report or feature request): bug report
Operating system (e.g. Fedora 24, Mac OS 10.11, Windows 10): Ubuntu 20.04
Platform (e.g. 64-bit x86, 32-bit ARM): x86_64
OpenSlide Python version (openslide.__version__): 1.1.2
OpenSlide version (openslide.__library_version__): 3.4.1
Slide format (e.g. SVS, NDPI, MRXS): NDPI

Details

I'm in trouble to retrieve regions from higher levels: images have huge artifacts as shown below:

I'm using this snippet, level = 6 in my case. (cx, cy) are in slide.dimensions range, (side_x,side_y) are not overflowing .
scale = 2**level
slide.read_region( location=(cx, cy), level=level, size=(side_x//scale, side_y//scale))

I can report the issue from level > 1
Strange enough, slide.read_region works well if i read at location=(0, 0)
The same script work fine in both cases under CentOS 7, by using the same python same libs version and the same .ndpi files
python 3.6 Pillow 6.2.1 numpy 1.19.5
Updating Pillow and different encoding (.jpg, .png) do not solve the issue.

[PerloDaniele]

Fixed by installing from source libpixman-1.so.0.40.0
http://www.linuxfromscratch.org/blfs/view/svn/general/pixman.html
Reference openslide/openslide#291