[jessedhillon]

This is hacker news -- I don't expect everyone to know how jbig2 or other compression scheme works. But before you insinuate that the scanner has semantic awareness of the document and is altering that meaning in a less-than-coincidental way, I would hope that you could have a cursory look at how such compression works.

The issue only involves small letters, because the compression scheme breaks up the image into patches and then tries to identify visually similar blocks and reuse them. Certain settings can allow for small blocks of text to be deemed identical, within a threshold, and thus replaced. That's all. Coincidence, not semantic awareness.

Hence the advisory notice to use a higher resolution -- smaller block sizes.

[cabalamat]

> The issue only involves small letters, because the compression scheme breaks up the image into patches and then tries to identify visually similar blocks and reuse them. Certain settings can allow for small blocks of text to be deemed identical, within a threshold, and thus replaced. That's all. Coincidence, not semantic awareness.

Copiers very commonly copy printed material. This sort of algorithm makes it likely that sometimes one character will be replaced by another, so it is a bad algorithm for the job.

Xerox should have known better.

[enraged_camel]

>>This is hacker news -- I don't expect everyone to know how jbig2 or other compression scheme works.

As opposed to what, ImageCompression News where you can expect everyone to know it?

[tbirdz]

Or maybe comp.compression

[Gormo]

I'm aware - I'm merely responding to the previous commenter's point about how the compression algorithm is "starting off with a bit mapped image that your brain happens to interpret as the number 17", and pointing out that if this were the case, the likely outcome should be a fuzzier-looking "17" and not a "21".

Clearly, the compression algorithm is designed around human perception (i.e. looking for visually-similar segments to, I assume, tokenize), and therefore does relate to the actual semantics of the document, albeit in a coarse and mechanical way. It did know enough to replace character glyphs with other character glyphs, but didn't know enough to choose the right ones.

My point is that it's not coincidental at all - this algorithm is obviously in a sort of "uncanny valley" in its attempt to model human visual perception.

[workbench]

You'd expect anyone who knows how JBIG2 works would also know it should never have been used for this