The lossless data compression fairies are having fun with me today...

• Scan 8.5" x 11" document at 1200dpi @ greyscale
• -> 60 MiB PNG, thank you
• Open PNG in GIMP, select a good threshold point, convert to 1bpp
• -> 514 KiB PNG
• Wait... 116:1 compression from 8-bit PNG to 1-bit PNG? HOW??
• convert to pdf
• "Warning, this file is really huge and may actually be a decompression bomb" lol, ok.
• -> 515 KiB PDF, nice
• ocrmypdf foo.pdf document.pdf
• -> 194 KiB PDF
• WHAT? HOW?!?
• pdfimages -png document.pdf foo
• -> 514 KiB PNG
• WHAT IS HAPPENING?!?

#PDF #PNG #Compression #greyscale

P.S., I found out that by default, ocrmypdf uses (lossless) #JBIG2 compression. That's why it was so well compressed. Also, the resultant PNG file at the end (which was basically the same PNG file that went into the PDF) was converted from JBIG — pdfimages converts images, it doesn't extract them in their natively stored format (but a -list will show you what the native format is). Also, I think pdfimages -all will just export the native format, whatever it is, but I haven't tried that yet.

Neat.. encountered the #xerox scanner bug live..

In case you don't remember, their #JBIG2 algorithm setttings causes small scanned symbols to be confused with symbols already in the compression dictionary and then misprinted.

In this case, the superscript "2" and "3" were turned into full size "2" and "3".

The nonsensical result, a #DnD whip does a 1D33 damage 🤣 if only 🤣

Interesting, both the German Federal Office for Information Security and the Swiss Coordination Office for the Permanent Archiving of Electronic Documents advise against the use of #JBIG2 compression in scanned #PDF documents.

This was prompted by the discovery in 2013 of the infamous "swapped characters" bug in Xerox photocopiers:

https://en.wikipedia.org/wiki/JBIG2#:~:text=not%20the%20same.%5B13%5D%5B14%5D%5B15%5D-,Character%20substitution%20errors%20in%20scanned%20documents,-%5Bedit%5D

Does anyone know if JPEG XL encoders can be prone to the infamous JBIG2 "Pattern Matching & Substitution" region-reuse issue, that so badly affected Xerox copiers?

https://www.dkriesel.com/en/blog/2013/0802_xerox-workcentres_are_switching_written_numbers_when_scanning

#JPEG #JPEGXL #JBIG2 #Xerox

Des formats d'image

#images #pictures #graphisme #jbig2 #GIF #JPEG #PNG #SVG #format #webp #heic #hevc #avi #eps #pdf #svg

https://lsdm.live/modules/news/article.php?storyid=4203

Are there any easy-to-use #JBIG2 tools for #Linux?

#GIMP doesn't seem to support it (yet?), and I just can't wrap my head around how to use jbig2enc -- it spits out some data to STDOUT that 'file' can't identify.
I just find the concept of lossy bilevel images compression fascinating, and I'd love to play with it to see how badly it would butcher something like a Floyd-Steinberg dithered image (and how much compression it'd actually accomplish)

This is 🤯:

“A Deep Dive Into An NSO Zero-Click iMessage Exploit: Remote Code Execution”, Project Zero, Google (https://googleprojectzero.blogspot.com/2021/12/a-deep-dive-into-nso-zero-click.html).

On HN: https://news.ycombinator.com/item?id=29568625

#Security #ComputerSecurity #Pegasus #NSOGroup #Apple #iMessage #Exploit #JBIG2