Editing Xerox (section)

==Character substitution bug==
In 2013, German computer scientist {{ill|David Kriesel (scientist)|de|David Kriesel|lt=David Kriesel}} discovered an [[Software bug|error]] in a Xerox WorkCentre 7535 copier. The device would substitute number digits in scanned documents, even when [[Optical character recognition|OCR]] was turned off. For instance, a cost table in a scanned document had an entry of 85.40, instead of the original sum of 65.40.<ref>{{cite web|url=http://www.dkriesel.com/en/blog/2013/0802_xerox-workcentres_are_switching_written_numbers_when_scanning|title=Xerox scanners/photocopiers randomly alter numbers in scanned documents|access-date=March 22, 2015|archive-date=August 3, 2013|archive-url=https://archive.today/20130803142236/http://www.dkriesel.com/en/blog/2013/0802_xerox-workcentres_are_switching_written_numbers_when_scanning|url-status=live}}</ref> After unsuccessfully trying to resolve this issue with Xerox's customer support, he publicised his findings on his blog. Providing example pages that would lead to the bug occurring, it was confirmed that this bug was reproducible on a wide variety of Xerox WorkCentre and other high-end Xerox copiers.

The source of the error was a bug in the [[JBIG2]] implementation, which is an image compression standard that makes use of pattern matching to encode identical characters only once. While this provides a high level of compression, it is susceptible to errors in identifying similar characters.

A possible workaround was published by Kriesel, which involved setting the image quality from "normal" to "higher" or "high". Shortly afterwards, it was found that the same fix had been suggested in the printer manual, which mentioned the occurrence of character substitutions in "normal mode", indicating that Xerox was aware of the software error.<ref>{{cite web|url=http://www.dkriesel.com/en/blog/2013/0806_work_around_for_character_substitutions_in_xerox_machines|title=Possible workaround for character substitutions in xerox machines|access-date=March 22, 2015|archive-date=February 9, 2015|archive-url=https://archive.today/20150209163226/http://www.dkriesel.com/en/blog/2013/0806_work_around_for_character_substitutions_in_xerox_machines|url-status=live}}</ref> In Xerox's initial response to a growing interest by the media, the error was described as occurring rarely and only when factory settings had been changed.<ref>{{cite news|url=https://www.bloomberg.com/bw/articles/2013-08-09/some-xerox-scanners-can-alter-documents-by-accident|title=Some Xerox Scanners Can Alter Documents by Accident|first=Peter|last=Coy|work=Businessweek.com|date=August 9, 2013|access-date=March 22, 2015|archive-date=February 10, 2015|archive-url=https://web.archive.org/web/20150210141525/http://www.bloomberg.com/bw/articles/2013-08-09/some-xerox-scanners-can-alter-documents-by-accident|url-status=live}}</ref><ref>{{cite web|url=https://www.zdnet.com/article/xerox-scanners-alter-numbers-in-scanned-documents/|title=Xerox scanners alter numbers in scanned documents|work=ZDNet|access-date=March 22, 2015|archive-date=February 7, 2015|archive-url=https://web.archive.org/web/20150207094044/http://www.zdnet.com/article/xerox-scanners-alter-numbers-in-scanned-documents/|url-status=live}}</ref> After Kriesel provided evidence that the error was also occurring in all three image quality modes (normal, higher and high) including the factory defaults, Xerox corrected their statement and released a software patch to eliminate the problem.<ref>{{cite web|url=http://www.pcworld.com/article/2046579/impact-of-xerox-charactersubstitution-bug-wider-than-thought.html|title=Impact of Xerox character-substitution bug wider than thought|first=Martyn|last=Williams|date=August 13, 2013|work=PCWorld|access-date=March 22, 2015|archive-date=February 7, 2015|archive-url=https://web.archive.org/web/20150207103444/http://www.pcworld.com/article/2046579/impact-of-xerox-charactersubstitution-bug-wider-than-thought.html|url-status=live}}</ref><ref>{{cite news|url=https://www.bbc.co.uk/news/technology-23610405|title=BBC News – Xerox to update scan software after switched number outcry|work=BBC News|date=August 7, 2013|access-date=March 22, 2015|archive-date=November 19, 2014|archive-url=https://web.archive.org/web/20141119133408/http://www.bbc.co.uk/news/technology-23610405|url-status=live}}</ref> Despite the problem being present in some instances also in higher quality mode, Xerox advises users that they can use this mode as an alternative to applying the patch.<ref>{{Cite web |url=http://www.xerox.com/assets/pdf/ScanningQAincludingAppendixA.pdf |title=Archived copy |access-date=February 8, 2015 |archive-date=November 29, 2015 |archive-url=https://web.archive.org/web/20151129083738/http://www.xerox.com/assets/pdf/ScanningQAincludingAppendixA.pdf |url-status=live }}</ref>