getting errors reading SVS macro and thumbnail images on Windows, not Linux

Benjamin Gilbert bgilbert at
Fri May 22 11:47:54 EDT 2015

Hi Toby,

On 05/21/2015 01:15 PM, Toby Cornish wrote:
> This has failed on all svs files I have tried. All the files have an
> embedded label, thumb, and macro image.  I can read all of them using
> the code below on Linux, but I can only read the label image under Windows.

I'm seeing the same problem with CMU-1.svs.  It's worse with CMU-1.ndpi 
and CMU-1.mrxs: neither of them will even open successfully. 
Interestingly, SVS label images are compressed with LZW, while the other 
associated images are JPEG.

The problem appears to be some compiler optimizations I enabled a few 
months ago.  Does last night's build fix the crashes for you?

For the record, the relevant crash was this one:

> WindowsError: exception: access violation reading 0x00000000

Python ctypes uses SEH to catch the access violation and prevent the 
entire process from crashing.  The openslide_t is then in an 
inconsistent state, and when we try to close the slide, we hit an 
assertion failure in OpenSlide:

> Openslide:ERROR:src/openslide-decode-tiff.c:699:_openslide_tiffcache_destroy:
> assertion failed: (tc->outstanding == 0)

--Benjamin Gilbert

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