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

Toby Cornish tcornis3 at
Sat May 23 12:00:47 EDT 2015

That seems to be working (output from my test svs on windows with this version):

python:  2.7.3 (default, Apr 10 2012, 23:31:26) [MSC v.1500 32 bit (Intel)]
version:  1.1.0
library_version:  3.4.1-g4be000b
associated_images.keys:  [u'label', u'macro', u'thumbnail']
label:  (680, 683)
macro:  (1600, 598)
thumb:  (666, 768)

I will do some more testing later tonight.



Date: Fri, 22 May 2015 11:47:54 -0400
From: Benjamin Gilbert <bgilbert at>
Subject: Re: getting errors reading SVS macro and thumbnail images on
	Windows, 	not Linux
To: openslide-users at
Message-ID: <555F4FAA.4030607 at>
Content-Type: text/plain; charset=windows-1252; format=flowed

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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