|Following reports of image substitution affecting copied numbers on a range of Xerox WorkCentre devices, the imaging company has started addressing the situation in a series of software patches. The company has "confirmed that errors can occur under a set of limited conditions when scanning 'stress documents' to PDF -- which can include very small font sizes, stray pixels and be difficult to read." The first batch of software updates is available now.
The first wave of products to be patched includes the Xerox ConnectKey family, WorkCentre 75xx, WorkCentre 57xx and ColorQube 93xx. Xerox will be adding the remainder of the affected products in Wave Two, which is scheduled to be available the week of August 26.
According to David Kriesel, the researcher that discovered the problem, "the error does not occur if PDFs are scanned with OCR, or TIFs are scanned (the latter seems plausible, as the pure image data should be saved into the TIF). Additionally, there seems to be a correlation between font size and scan dpi used. I was able to reliably reproduce the error for 200 DPI PDF scans without OCR, of sheets with Arial 7pt and 8pt numbers."
Since original discovery, the error has been linked to overzealous compression within the scanner and printer combination. The JBIG2 algorithm, when used in "normal" mode (but not higher levels) has been found to make the substitution during copy or document saving operations when OCR is not being used.
The error is beyond a simple "8 for 6" exchange, as the JBIG2 routine "creates a dictionary of image patches it finds 'similar.' Those patches then get reused instead of the original image data, as long as the error generated by them is not 'too high'." Xerox confirmed the problem with the researcher in a conference call a few days after the discovery.