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114 lines
4.2 KiB
Plaintext
114 lines
4.2 KiB
Plaintext
Twibright Optar
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---------------
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This is a program to store data on paper using a 600dpi b/w laser printer and a
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600+ dpi scanner.
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You need to install ImageMagick so that the resulting .pgm image can be converted into
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PostScript with the right dimensions (so each pixel is 3x3 600dpi pixels so that
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there is no unnecessary jitter).
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Make sure you have libpng installed and if you type "libpng-config" on the
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commandline, there's a program which prints something.
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Compile with "make". Become root (su -) and type "make install". Now you have
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optar, unoptar and pgm2ps installed on your system in /usr/local/bin. Later
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you can uninstall by typing "make uninstall" the same way as you typed
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"make install".
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Encoding (writing)
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------------------
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Run
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./optar other_guys.ogg other_guys.ogg
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which will produce files:
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other_guys.ogg_0001.pgm
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other_guys.ogg_0002.pgm
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other_guys.ogg_0003.pgm
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other_guys.ogg_0004.pgm
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other_guys.ogg_0005.pgm
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other_guys.ogg_0006.pgm
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Now convert them into PostScript using the included pgm2ps tool:
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./pgm2ps *.pgm
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Print them using a 600dpi (or more) laser printer. Inkjet or dot matrix was
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never tested and will not probably work at the pre-defined data density. See
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"Changing the format" below.
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Please note that the file will be padded by zeroes and the original length will
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be lost. Pack your data with tar if you store data that are sensitive to this.
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Decoding (reading)
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------------------
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Clean and polish the scanner glass with rubbing alcohol and paper towel. Put
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yellow pages on the scanner lid to get sharper picture *). Insert the
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page so that the text on the bottom is upright. Scan the pages into
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PNG (not JPEG!) on 600dpi (or 1200dpi, slightly better):
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scan_0001.png
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scan_0002.png
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scan_0003.png
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scan_0004.png
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scan_0005.png
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scan_0006.png
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Read the number sequence (format specification) from any of the papers and feed
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it as 1st argument to the optar, 2nd argument is the filename part before the
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underscore:
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unoptar 0-65-93-24-3-1-2-24 scan > out.ogg
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Then play out.ogg with mplayer. You should get first about 41 seconds from the
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Ogg Vorbis file.
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*) In the scanner I tried (Canoscan), the lid didn't seem to be heavy enough to
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press the paper down completely - there were blurry spots in the picture.
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Without yellow pages I got 526 reparable bad bits bad from 3.2 million. With
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yellow pages the blurry spots were much sharper and I got only 261 reparably
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bad bits!
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Please note the data are padded with zeroes so the original information
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about file length is lost. If your data format doesn't like this then first
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pack your data with tar.
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A4 <-> US Letter
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----------------
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Change the convert parameters in pgm2ps (see comments). Change XCROSSES
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and YCROSSES in optar.h (see comments). Recompile. Then you can use US Letter
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instead of A4.
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Changing the format
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-------------------
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If your printer is low quality and you are getting irreparable bits, you can
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try to format the media to lower capacity. Unfortunately, setting by
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commandline is not implemented yet. Change XCROSSES and YCROSSES in optar.h to
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lower values which yields bigger pixels and lower capacity per page, but higher
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reliability. Make sure they are in roughly the same proportion as before,
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otherwise you get nonsquare pixels and unnecessary waste of channel capacity.
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You can also change the decoding parameters in unoptar.c (look for MAGIC
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CONSTANTS) in attempt to read a difficult recording: unsharp_mask,
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unsharp_dist, sync_white_cut, white_cut, minmax_filter, pixel_blur, cross_trim.
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Future improvement
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==================
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- manpage could be written for optar and unoptar
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- commandline help (-h) could be written for optar and unoptar
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- the format could be made configurable. Now it's stored in the optar.h
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- the magic constants could be changed by commandline options. Now they are
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stored in unoptar.c.
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- Golay code decoding could be rewritten faster, using a sophisticated
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algorithm (Kasami algorithm?)
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- Easy support for multiple pages per page, so it can be read by a digital
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camera. Currently it cannot since digital camera blurs at the sides of
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the picture.
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(c) GPL 2007 Karel 'Clock' Kulhavy of Twibright Labs
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See COPYING for the text of the GPL license.
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e-mail: clock (at) twibright (dot) com
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Twibright Optar homepage: http://ronja.twibright.com/optar/
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