On Sun, May 31, 2015 at 4:25 PM, Jay Smith <j...@jaysmith.com
<mailto:j...@jaysmith.com>> wrote:

    Greetings fellow Gimp Users,

    I make images using Gimp, but I assume that this question is not
    really Gimp specific.

    I have tens of thousands of images (postage stamps) on my site.
    Every now and then when I am looking at a page I discover that the
    image (a JPEG) has had is colors "sort of inverted".  The JPEGs were
    created in large batches by a script from UNcompressed TIFF images.
    When I go back and look at the the original TIFF, I discover that
    its colors are "sort of inverted" -- thus the JPEG is a correct
    rendition of the appearance of its TIFF source.

    Thus the problem is in the TIFF.  But, the problem happens now and
    then, over the course of years.  The TIFFs are _not_ being
    intentionally manipulated in that time.  The images was originally
    okay, now its not.  It seems to be completely random, just one image
    here and there.

    Somehow the TIFF is getting corrupted.  I am assuming by a memory
    error or a disk/RAID controller error, or such.  The images are
    still openable in Gimp.

    This is only happening to one out perhaps one out of five thousand
    images, every five years.  (I am just *guessing* at the error rate
    because I only find out about them by randomly coming across them.)
    But, if I have 40,000 images, that is eight images destroyed every
    five years.  (And often I am not able to replace the image because I
    no longer have the item.)

    This example image was originally created in 2006.  I suspect
    (mostly guessing) that it was corrupted sometime since 2010.  There
    is no reason that it would have been edited since that time and file
    modification information shows nothing since 2006.

    On Ubuntu Linux, using "identify -verbose filename.tif" I can read
    the header information.  The only odd thing (to my eye) is that the
    create date is 2011 and the modification date is 2006:

    Properties:
         date:create: 2011-09-13T11:30:24-04:00
         date:modify: 2006-12-21T00:53:03-05:00

    I am guessing that means the corruption may have happened in 2011,
    even though the filesystems own file datestamp is 2006 and the
    lsattr command shows nothing unusual.


    Here is example of a) the resulting JPEG (just to illustrate the
    nature of the corruption); b) a similar JPEG to show generally what
    it is supposed to look like; c) the corrupted TIFF.

    Corrupted:
    
http://jsa.viewimage.net/jsa/web/Lists/Denmark/AdPairs/Spec/re02-pair_used-vf-b_136468_r_l.jpg

    Correct image of a similar, but different item:
    
http://jsa.viewimage.net/jsa/web/Lists/Denmark/AdPairs/Spec/re02-pair_used-vf-a_136467_r_l.jpg

    This is the TIFF file (corrupted, but viewable in Gimp; colors are
    sort-of-inverted)  Size 496 KB:
    http://jsa.viewimage.net/temp/gimp/re02-pair_used-vf-b_136468.tif

    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?

    Any thoughts appreciated.

    Jay


On 05/31/2015 08:46 PM, Daniel Smith wrote:
> when you say youre seeing thison a web page,
> can i ask what type of system yure serving the pages with?
> wordpress etc? or is it an image generation with php or something?
> thanks
> dan


Hi Dan,

When I say I saw it on a web page, all I meant is that was where I was looking when I noticed the corrupted file (JPEG version thereof).

All viewing (of both the JPEG and the original TIFF that the JPEG was made from) after that time has been done using Gimp to view the corrupted files.

The fact that I first noticed the corrupted JPEG on a web page was not relevant and I should not have included that detail. I only mentioned it that way because that is the only way I actually would notice that one of tens of thousands of files had been corrupted. I don't systematically go through and view the library of files just for fun.

I am sorry for the misleading detail.

Jay
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