Twibright Optar

Special note: The repository of optar at http://github.com/colindean/optar exists because I (@colindean) had difficulties finding the source and it seemed to be abandoned/dormant. I've made slight improvements over time. Improvements welcomed as pull requests.

This is a program to store data on paper using a 600 dpi black and white laser printer and a 600+ dpi scanner.

Building

You need to install ImageMagick so that the resulting .pgm image can be converted into PostScript with the right dimensions: each pixel must be 3x3 600dpi pixels so that there is no unnecessary jitter.

Make sure you have libpng installed. You'll know that is is installed correctly if you type libpng-config on the commandline, there's a program which prints something. Virtually all desktop Linux distros and every macOS system has this installed already.

Compile with

make

Note that there may be some hardcoded configuration values that you may need to change, for example the page size defaults to A4 instead of US Letter. Read on to learn where to change that.

Installing locally

It's easiest to install your local build with

sudo make install

optar, unoptar, and pgm2ps installed on your system in /usr/local/bin.

To uninstall, run

sudo make uninstall

Encoding (writing)

Run

optar other_guys.ogg other_guys.ogg

which will produce files:

other_guys.ogg_0001.pgm
other_guys.ogg_0002.pgm
other_guys.ogg_0003.pgm
other_guys.ogg_0004.pgm
other_guys.ogg_0005.pgm
other_guys.ogg_0006.pgm

Now convert them into PostScript using the included pgm2ps tool:

pgm2ps *.pgm

Print these using a 600 dpi (or greater resolution) laser printer. Inkjet or dot matrix was never tested and will not probably work at the pre-defined data density. See "Changing the format" below.

Please note that the file will be padded by zeroes and the original length will be lost. Pack your data with tar if you store data that are sensitive to this.

Decoding (reading)

Clean and polish the scanner glass with rubbing alcohol and paper towel. Put yellow pages on the scanner lid to get sharper picture˚. Insert the page so that the text on the bottom is upright. Scan the pages into PNG (not JPEG!) on 600dpi (or 1200dpi, slightly better):

scan_0001.png
scan_0002.png
scan_0003.png
scan_0004.png
scan_0005.png
scan_0006.png

Read the number sequence (format specification) from any of the papers and feed it as 1st argument to the optar, 2nd argument is the filename part before the underscore:

unoptar 0-65-93-24-3-1-2-24 scan > out.ogg

Then play out.ogg with mplayer. You should get first about 41 seconds from the Ogg Vorbis file.

˚ In the scanner I tried (Canoscan), the lid didn't seem to be heavy enough to press the paper down completely - there were blurry spots in the picture. Without yellow pages I got 526 reparable bad bits bad from 3.2 million. With yellow pages the blurry spots were much sharper and I got only 261 reparably bad bits!

Please note the data are padded with zeroes so the original information about file length is lost. If your data format doesn't like this then first pack your data with tar.

A4 <-> US Letter

Change the convert parameters in pgm2ps (see comments). Change XCROSSES and YCROSSES in optar.h (see comments). Recompile. Then you can use US Letter instead of A4.

Changing the format

If your printer is low quality and you are getting irreparable bits, you can try to format the media to lower capacity. Unfortunately, setting by commandline is not implemented yet. Change XCROSSES and YCROSSES in optar.h to lower values which yields bigger pixels and lower capacity per page, but higher reliability. Make sure they are in roughly the same proportion as before, otherwise you get nonsquare pixels and unnecessary waste of channel capacity.

You can also change the decoding parameters in unoptar.c (look for MAGIC CONSTANTS) in attempt to read a difficult recording: unsharp_mask, unsharp_dist, sync_white_cut, white_cut, minmax_filter, pixel_blur, cross_trim.

Future improvement

manpage could be written for optar and unoptar
commandline help (-h) could be written for optar and unoptar
the format could be made configurable. Now it's stored in the optar.h
the magic constants could be changed by commandline options. Now they are stored in unoptar.c.
Golay code decoding could be rewritten faster, using a sophisticated algorithm (Kasami algorithm?)
Easy support for multiple pages per page, so it can be read by a digital camera. Currently it cannot since digital camera blurs at the sides of the picture.

Authorship and Licensing

See COPYING for the text of the GPL license.

e-mail: clock (at) twibright (dot) com

Twibright Optar homepage: http://ronja.twibright.com/optar/