[sane-devel] compression used on Lexmark lx2480

Aapo Tahkola aet at rasterburn.org
Thu Oct 25 04:15:26 UTC 2007


This device is seems to be based on some custom soc (arm9 or mips
probably). I have tried to make some sense out of the data and have
found out that shortest repeating pattern on completely white is 6 bits
long. This pattern is 1010 00 or some other variation of same pattern of
one's. I have also found out that when there's some other color on the
input, this "exception" seems to start with 1010 01 or 1010 11.
There's a good example on line 16 of 203.d 
For colored scans white is 1010 0000 0000 00.

I'm guessing that one 6 bit white accounts for 64 pixels.  xres *
yres / number of 6 bit sequences on one usb bulk packet / number of
bulk packets.
2400 * 3000 / 187.0 / 599.0 = ~64.27 . This would seem
more than just a coincidence 
Unfortunately completely black scan don't seem possible due to
noise. I even tried killing leds that light the paper...

Anyway, do you have any idea what compression algorithm could this be?
usbmon dumps and images are at http://www.rasterburn.org/~aet/lx2480/ .
I have stripped out everything but incoming bulk messages from that

Aapo Tahkola

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