On 05/31/2015 07:09 PM, Liam R. E. Quin wrote:
On Sun, 2015-05-31 at 17:25 -0400, Jay Smith wrote:

My primary question is whether there is a "particular bit that is
getting flipped" that could be "unflipped" by some sort of non-visual
editing of the source TIFF file?

My secondary question is whether or not other people have seen this
type of problem crop up in large image libraries and what the causes
have been?

The nearest I have seen to this that i can remember involves software
changes - e.g. a different version of libtiff or whatever. For
example, recently some images on  http://www.fromoldbooks.org/appeared
to break, and it turned out to be a version of the jpeg library that
had stopped supporting arithmetic encoding (for software patent

TIFF is one of the more complex graphics formats in widespread use;
for my own part I prefer to use PNG because at least the core image
part is relatively simple and well-specified and widely supported.

If by any chance you have both an "uncorrupted" and a "corrupted" TIFF
file, and you know for sure what programs were used to create them and
on what platform (e.g. Linux on SPARC, Linux on Intel-64, 32-bit
Windows on Intel, etc) I'm willing to take a look, althogh I don't
think I have TIFF debugging stuff around any more.

It seems unlikely that the same single-bit error would happen on
multiple images because of a hard drive problem, especially if a RAID 3
or higher storage system didn't detect it. Not impossible - an
infinite number of monkeys typing for all eternity might all type
nothing except page 54 of the January 1936 Great Western Railway
timetable through Crewe - but I'd look for more likely causes first,
the most likely of which might be a software change.



Thanks for your thoughts.

I am not understanding how a different version of "libtiff or whatever" could result in the corruption of a very few random TIFF image files (each just one of tens of thousands), every now and then, that are just sitting there, not actively being used by any process (that I am aware of).

If the corruption happened to many files that were being processed in the same manner, from time to time, then I would understand.

As for my idea about a memory or controller error on the server causing corruption, I certainly agree with you that it does not seem likely that the corruption would be of exactly the same type on the files that are affected, and that I have _not_ detected corruption of any other types of files or programs.

So, that leaves back to not having any explanation at all.  :-)

Thanks again,

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