import from http://ronja.twibright.com/optar/

README

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+Twibright Optar
+---------------
+
+This is a program to store data on paper using a 600dpi b/w laser printer and a
+600+ dpi scanner.
+
+You need to install ImageMagick so that the resulting .pgm image can be converted into
+PostScript with the right dimensions (so each pixel is 3x3 600dpi pixels so that
+there is no unnecessary jitter).
+
+Make sure you have libpng installed and if you type "libpng-config" on the
+commandline, there's a program which prints something.
+
+Compile with "make". Become root (su -) and type "make install". Now you have
+optar, unoptar and pgm2ps installed on your system in /usr/local/bin. Later
+you can uninstall by typing "make uninstall" the same way as you typed
+"make install".
+
+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 them using a 600dpi (or more) 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.
+
+(c) GPL 2007 Karel 'Clock' Kulhavy of Twibright Labs
+See COPYING for the text of the GPL license.
+e-mail: clock (at) twibright (dot) com
+Twibright Optar homepage: http://ronja.twibright.com/optar/