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Xerox scanners and photocopiers randomly alter numbers in scanned documents

dkriesel.com

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Re: Xerox scanners and photocopiers randomly alter numbers in scanned documents

#11

Post by simonster »

ElliotH wrote: post #3

I can't quite see the reason why you would lossily compress something when your machine's purpose is to duplicate things. Anyone got a reasonable reason for doing this?

If you're scanning a long document to a PDF, compression makes a lot of sense. It's the difference between being able to email the PDF as an attachment and having to find a place to put the file online.

Re: Xerox scanners and photocopiers randomly alter numbers in scanned documents

#12

Post by rly_ItsMe »

ElliotH wrote: post #3

I can't quite see the reason why you would lossily compress something when your machine's purpose is to duplicate things. Anyone got a reasonable reason for doing this?

In the good old days of analog copiers this would be impossible - the scanner send the light through a system of mirrors to the drum, the drum gets static charged, the toner is pulled on the charged parts and gets transferred to the transfer belt, here the paper has the opposite charge and pulls the toner off of the transfer belt, goes through the fusing unit and here is the toner 'burned' to the paper. End of Story

On a modern copier the scanner transfers the data first to RAM and than usually to a hard disk (the most of the people do not even know that the "copy machine" has one and saves the scanned stuff to it). From that hard disk the data where transmitted via laser to the drum

Tadaaa - you have the reason for having data be compressed on a modern copier.

Re: Xerox scanners and photocopiers randomly alter numbers in scanned documents

#14

Post by agl »

This class of error is called (by me, at least) a "contoot" because, long ago, when I was writing the JBIG2 compressor for Google Books PDFs, the first example was on the contents page of book. The title, "Contents", was set in very heavy type which happened to be an unexpected edge case in the classifier and it matched the "o" with the "e" and "n" and output "Contoots".

The classifier was adjusted and these errors mostly went away. It certainly seems that Xerox have configured things incorrectly here.

Also, with Google Books, we held the hi-res original images. It's not like the PDF downloads were copies of record. We could also tweak the classification and regenerate all the PDFs from the originals.

For a scanner, I don't think that symbol compression should be used at all for this reason. For a single page, JBIG2 generic region encoding is generally just as good as symbol compression.

More than you want to know about this topic can be found here: https://www.imperialviolet.org/binary/google-books-pdf.pdf

Re: Xerox scanners and photocopiers randomly alter numbers in scanned documents

#17

Post by MoreConsiderate »

Gravityloss wrote: post #9
gcr wrote: post #5

Earlier quoted context omitted.

That's quite possible. http://www.cs.columbia.edu/CAVE/projects/face_replace/ I can imagine someone turning the technique into a novel form of image compression, maybe for surveillance databases or something.

Think how someone could falsify your entire life...

Accept it as an inevitability and develop skills that enable you to adapt, react & procreate in a multitude of diverse situations.

Re: Xerox scanners and photocopiers randomly alter numbers in scanned documents

#18

Post by lostlogin »

gcr wrote: post #5
nsxwolf wrote: post #4

Truly surprising. I would never have imagined this to be in the domain of possible problems one would expect to encounter scanning or photocopying a document. It is like taking a picture of my wife with a digital camera and her face being replaced with that of some other person.

That's quite possible. http://www.cs.columbia.edu/CAVE/projects/face_replace/ I can imagine someone turning the technique into a novel form of image compression, maybe for surveillance databases or something.

A very tech savvy friend bought a camera in Japan and after about a week or started delving into settings. He thought all the faces looked wrong. He found a setting that made the eyes bigger and rounder. It was subtle, but quite funny at the same time.

Re: Xerox scanners and photocopiers randomly alter numbers in scanned documents

#19

Post by algorias »

simonster wrote: post #11
ElliotH wrote: post #3

I can't quite see the reason why you would lossily compress something when your machine's purpose is to duplicate things. Anyone got a reasonable reason for doing this?

If you're scanning a long document to a PDF, compression makes a lot of sense. It's the difference between being able to email the PDF as an attachment and having to find a place to put the file online.

Exactly, and that is why there should be a compression step on the code path that handles the paper -> pdf case. This doesn't make any sense in a paper -> paper case, however, as any electronic version of the image will only be stored internally, for a very brief time.

Re: Xerox scanners and photocopiers randomly alter numbers in scanned documents

#20

Post by lostlogin »

simonster wrote: post #11
ElliotH wrote: post #3

I can't quite see the reason why you would lossily compress something when your machine's purpose is to duplicate things. Anyone got a reasonable reason for doing this?

If you're scanning a long document to a PDF, compression makes a lot of sense. It's the difference between being able to email the PDF as an attachment and having to find a place to put the file online.

It is amazing the things people expect to be emailed. Can you email me the MRI scan? It's over 1500 images. Can you email it?
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