Barcode Writer in Pure Postscript

                      Terry Burton tez@terryburton.co.uk

Abstract:

This document describes the implementation of the Barcode Writer in Pure
Postscript project, explains by example how to use this to generate your own
barcodes, and provides a simple reference to using the symbologies that it
supports.


Contents


* Introduction
* Code_Commentary

  o The_Barcode_Data_Structure
  o An_Encoder
  o The_Renderer
  o Notes_Regarding_Coding_Style


* Resources_and_Examples

  o Language_Specific_APIs
  o Front_Ends
  o Installing_the_Barcode_Generation_Capability_into_a_Printer's_Virtual
    Machine
  o Hints_for_Generating_Precisely_the_Required_Symbol
  o Printing_in_Perl


* Supported_Symbologies

  o EAN-13
  o EAN-8
  o UPC-A
  o UPC-E
  o EAN-5
  o EAN-2
  o ISBN
  o Code-39
  o Code-128_and_UCC/EAN-128
  o Rationalized_Codabar
  o Interleaved_2_of_5_and_ITF-14
  o Code_2_of_5
  o Postnet
  o Royal_Mail
  o MSI
  o Plessey


* License



Introduction

Often there is a need to implement routines in several different languages that
output Adobe Postscript for the purpose of printing barcodes. This project
implements the printing of barcodes entirely within level 2 PostScript. This
means that the entire process of converting the input string into the printed
output is performed by the printer or print system, thus avoiding the need to
later reimplement the barcode generation process when your development language
changes.
To make it as easy as possible to incorporate this project into your own
systems, whether they be freely available or proprietary, it is licensed under
the permissive MIT/X-Consortium License given in section 5.
The project homepage is at http://www.terryburton.co.uk/barcodewriter.
This is the main resource for the project providing the latest downloads of
code and documentation, as well as access to the support and development
mailing list.


Acknowledgements

The author wishes to take this opportunity to thank the small, growing
community of developers that have helped to develop, test and document this
project with their suggestions and code. Most especially Michael Landers and
Ross McFarland for freely giving their encoder implementations, and Lawrence
Horwitz for his suggestions and testing.


Code Commentary

This commentary assumes familiarity with the PostScript language1.
The code is split cleanly into two types of procedure:


  The encoders
      Each of these represents a barcode symbology2, e.g. EAN-13 or Code-128.
      It takes a string containing the barcode data and a string containing a
      list of options that modify the output of the encoder. It generates a
      structured representation of the barcode and its text for the symbology,
      including the calculation of check digits where necessary.

  The renderer
      This takes the output of an encoder and generates a visual representation
      of the barcode.

This means that all barcodes can be generated simply in a similar manner:

  (78858101497) (includetext height=0.6) upca barcode
  (0123456789) (includecheck) interleaved2of5 barcode



The Barcode Data Structure

The following table describes the structured representation of a barcode that
is passed by an encoder to the renderer as a dictionary when the PostScript is
executed.
 _____________________________________________________________________________
|Element______________|Key|Value______________________________________________|
|Space bar succession |sbs|String containing the integer widths, in points, of|
|_____________________|___|each_bar_and_space,_starting_with_the_leftmost_bar.|
|Bar height succession|bhs|Array containing the height of each bar in inches, |
|_____________________|___|starting_with_the_leftmost_bar.____________________|
|Bar base succession  |bbs|Array containing the offset of the base of each bar|
|_____________________|___|in_inches,_starting_with_the_leftmost_bar._________|
|                     |   |Array of arrays that contain the character,        |
|Human readable text  |txt|position, height, font and scale factor (font      |
|                     |   |size), in points, for each of the visible text     |
|_____________________|___|characters.________________________________________|
|Renderer options     |opt|String containing the user-defined renderer        |
|_____________________|___|options.___________________________________________|


An Encoder

The procedure labelled code2of5 is a simple example of an encoder, which we
will now consider. Its purpose is to accept as input a string containing the
barcode contents and a string containing a list of options, and to process
these in a way that is specific to this encoder, and finally to output an
instance of the dictionary-based data structure described in section 2.1 that
represents the barcode contents in the Code 2 of 5 symbology.
As with all of the encoders, the input string is assumed to be valid for the
corresponding symbology, otherwise the behaviour is undefined.
The variables that we use in this procedure are confined to local scope by
declaring the procedure as follows:

  /code2of5 {

       0 begin

  ...

       end

  } bind def
  /code2of5 load 0 1 dict put

We start by immediately reading the contents strings that are passed as
arguments to this procedure by the user. We duplicate the options string
because it is later passed unamended to the renderer.

       /options exch def
       /renderopts options def
       /barcode exch def

We initialise a few default variables. Those variables corresponding to options
that can be enabled with the options argument are initially set to false.

       /includetext false def
       /textfont /Courier def
       /textsize 10 def
       /textpos -7 def
       /height 1 def

The options string is tokenised with each successive token defining either a
name value pair which we instantiate or a lone variable that we define as true,
allowing us to override the given default variables given above.

  options {
      token false eq {exit} if dup length string cvs (=) search
      true eq {cvlit exch pop exch def} {cvlit true def} ifelse
  } loop

Since any user given options create variables that are strings we need to
convert them back to their intended types.

  /textfont textfont cvlit def
  /textsize textsize cvr def
  /textpos textpos cvr def
  /height height cvr def

We then create an array of string encodings for each of the available
characters which we then declare in another string. This information can be
derived from careful reading of the relevant specification, although this is
often surprisingly difficult to obtain.

       /encs
       [ (1111313111) (3111111131) (1131111131) (3131111111)
         (1111311131) (3111311111) (1131311111) (1111113131)
         (3111113111) (1131113111) (313111) (311131)
       ] def

       /barchars (0123456789) def

We now store the length of the content string and calculate the total number of
bars and spaces in the resulting barcode. We initialise a string of size
dependant on this length into which we will build the space bar succession.
Similarly, we create an array into which we will add the human readable text
information.

       /barlen barcode length def
       /sbs barlen 10 mul 12 add string def
       /txt barlen array def

We now begin to populate the space bar succession by adding the encoding of the
start character to the beginning.

       sbs 0 encs 10 get putinterval

We now enter the main loop which iterates over the content string from start to
finish, looking up the encoding for each character, adding this to the space
bar succession.
It is important to understand how the encoding for a given character is
derived. Firstly, given a character, we find its position in the string of all
available characters. We then use this position to index the array of character
encodings to obtain the encoding for the given character, which is added to the
space/bar succession. Likewise, the character is added to the array of human
readable text along with positioning and font information.

      0 1 barlen 1 sub {
          /i exch def
          barcode i 1 getinterval barchars exch search
          pop
          length /indx exch def
          pop pop
          /enc encs indx get def
          sbs i 10 mul 6 add enc putinterval
          txt i [barcode i 1 getinterval i 14 mul 10 add -7
                 textfont textsize] put
      } for

The encoding for the end character is obtained and added to the end of the
space bar succession.

      sbs barlen 10 mul 6 add encs 11 get putinterval

Finally we prepare to push a dictionary containing the space bar succession
(and any additional information defined in section 2.1) that will be passed to
the renderer.

       /retval 1 dict def
       retval (sbs) sbs put
       retval (bhs) [sbs length 1 add 2 idiv {height} repeat] put
       retval (bbs) [sbs length 1 add 2 idiv {0} repeat] put
       includetext {
           retval (txt) txt put
       } if
       retval (opt) renderopts put
       retval


The Renderer

The procedure labelled barcode is known as the renderer, which we now consider.
Its purpose is to accept as input an instance of the dictionary-based data
structure described in section 2.1 that represents a barcode in some arbitrary
symbology and produce a visual rendering of this at the current point.
The variables that we use in this procedure are confined to local scope by
declaring the procedure as follows:

  /barcode {

       0 begin

  ...

       end

  } bind def
  /barcode load 0 1 dict put

We then immediately read the dictionary-based data structure which is passed as
a single argument to this procedure by an encoder, from which we extract the
space bar succession, bar height succession and bar base succession.

      /args exch def
      /sbs args (sbs) get def
      /bhs args (bhs) get def
      /bbs args (bbs) get def
      /renderopts args (opt) get def

We attempt to extract from the dictionary the array containing the information
about human readable text. However, this may not exist in the dictionary in
which case we create a default empty array.

      args (txt) known {
          /txt args (txt) get def
      } {
          /txt [] def
      } ifelse

Just as with the encoders, we read and tokenise the supplied options allowing
specific rendering options to be overridden.

      /inkspread 0.15 def
      renderopts {
          token false eq {exit} if dup length string cvs (=) search
          true eq {cvlit exch pop exch def} {cvlit true def} ifelse
      } loop
      /inkspread inkspread cvr def

We have extracted or derived all of the necessary information from the input,
and now use the space bar succession, bar height succession and bar base
succession in calculations that create a single array containing elements that
give coordinates for each of the bars in the barcode.
We start by creating a bars array that is half the length of the space bar
succession. We build this by repeatedly adding array elements that contain the
height, x-coordinate, y-coordinate and width of single bars. The height and y-
coordinates are read from the bar height succession and the bar base
succession, respectively, whilst the x-coordinate and the width are made from a
calculation of the total indent, based on the space bar succession and a
compensating factor that accounts for ink spread.


      /bars sbs length 1 add 2 idiv array def
      /x 0.00 def
      0 1 sbs length 1 sub {
          /i exch def
          /d sbs i get 48 sub def
          i 2 mod 0 eq {
              /h bhs i 2 idiv get 72 mul def
              /c d 2 div x add def
              /y bbs i 2 idiv get 72 mul def
              /w d inkspread sub def
              bars i 2 idiv [h c y w] put
          } if
          /x x d add def
      } for

Finally, we perform the actual rendering in two phases. Firstly we use the
contents of the bars array that we just built to render each of the bars, and
secondly we use the contents of the text array extracted from the input
argument to render the text. We make an efficiency saving here by not
performing loading and rescaling of a font if the scale factor for the font
size is 0. The graphics state is preserved across calls to this procedure to
prevent unexpected interference with the users environment.

      gsave

      bars {
          {} forall
          setlinewidth moveto 0 exch rlineto stroke
      } forall

      txt {
          {} forall
          dup 0 ne {exch findfont exch scalefont setfont}
          {pop pop}
          ifelse
          moveto show
      } forall

      grestore


Notes Regarding Coding Style

PostScript programming veterans are encouraged to remember that the majority of
people who read the code are likely to have little, if any, prior knowledge of
the language.
To encourage development, the code has been written with these goals in mind:


  -
      That it be easy to use and to comprehend

  -
      That it be easy to modify and enhance

To this end the following points should be observed for all new code
submissions:


  -
      New encoders should be based on the code of a similar existing encoder

  -
      Include comments where these clarify the operations involved, particular
      where something unexpected happens

  -
      Prefer simplicity to efficency and clarity to obfuscation, except where
      this will be a problem



Resources and Examples

There are several ways of using the PostScript within your own projects.
Many example uses of the code for various languages and platforms can be
downloaded from the code repository at http://www.terryburton.co.uk/
barcodewriter/files/repository/

Language Specific APIs

No language specific APIs exist yet. If you have experience writing API
specifications and would like to help create an API design for the project then
contact the author.

Front Ends

The following is a list of the front ends available for the project.


  Web based demo
      http://www.raise-the-bar.co.uk/demo

  pst-barcode
      pst-barcode is a PSTricks package for LATEX.
      http://www.ctan.org/tex-archive/graphics/pstricks/contrib/pst-barcode/


Installing the Barcode Generation Capability into a Printer's Virtual Machine

Most genuine PostScript printers allow procedures to be defined such that they
persist across different jobs through the use of the exitserver command. If
your printer supports this then you will be able to print the main code
containing the definitons of all the encoders and the renderer once, e.g. soon
after the device is turned on, and later omit these definitons from each of the
barcode documents that you print.
To install the barcode generation capabilities into the virtual machine of a
PostScript printer you need to uncomment a line near the top of the code so
that it reads:

  serverdict begin 0 exitserver

Once this code is printed the procedural definitions for the encoders and the
renderer will remain defined across all jobs until the device is reset either
by power-cycling or with the following code:

  serverdict begin 0 exitserver systemdict /quit get exec


Hints for Generating Precisely the Required Symbol

To create a barcode to a required width and height, without stretching the
human readable text, perform the following steps.
Create a basic symbol by choosing the relevant data and text options for the
corresponding encoder, and position this using translate such that the bottom-
left corner of the bars is in the required location:

  gsave
  430 750 translate
  (977147396801) (includetext) ean13 barcode
  grestore

Find the uniform scale factor (same value for x and y) that makes your output
of the required width:

  gsave
  430 750 translate
  1.3 1.3 scale      %  <-- Add a line like this
  (977147396801) (includetext) ean13 barcode
  grestore

Add a height option that adjusts the bar height appropriately (taking the
scaling into account):

  gsave
  430 750 translate
  1.3 1.3 scale
  % Added height=0.8 option to adjust height
  (977147396801) (includetext height=0.8) ean13 barcode
  grestore

The result should now be of the intended dimensions at the desired location
with properly scaled text. You can now add any additional options to customise
the symbol.

Printing in Perl

This example will print a page of EAN-13s ranging between two given values when
called from a shell like this:

  $ ./ean13s.pl 978186074271 978186074292 | lpr

The contents of the script ean13s.pl is as follows:

  #!/usr/bin/perl -w
  use strict;

  die 'Requires two arguments' if (@ARGV!=2);

  open(PS,'barcode.ps') || die 'File not found';
  $_=join('',<PS>);
  close(PS);

  print "%!PS-Adobe-2.0\n";

  m/
      %\ --BEGIN\ TEMPLATE--
      (.*)
      %\ --END\ TEMPLATE--
      /sx || die 'Unable to parse out the template';
  print $1;

  for (my $i=$ARGV[0], my $j=0; $i<$ARGV[1]; $i++, $j++) {
      my $x=100+150*(int($j/7));
      my $y=100+100*($j%7);
      print "gsave\n";
      print "$x $y translate\n";
      print "($i) (includetext) ean13 barcode\n";
      print "grestore\n";
  }

  print "showpage\n";



Supported Symbologies

The following section shows the symbologies that are supported by the encoders,
including the available features for each. This list may not be up-to-date. If
it does not contain any of the formats or features that you require then check
the project source code or try the support mailing list.

EAN-13



  Data
      12 or 13 digits

  Options
       ______________________________________
      |Option_____|Feature___________________|
      |includetext|Enable_human_readable_text|


  Notes
      If just 12 digits are entered then the check digit is calculated
      automatically

                                       Figure
                                       1:
                                       (9781860742712)
                                       (includetext
                                       guardwhitespace)
                                       ean13
                                       barcode


EAN-8



  Data
      8 digits

  Options
       ______________________________________
      |Option_____|Feature___________________|
      |includetext|Enable_human_readable_text|


                                       Figure
                                       2:
                                       (12345678)
                                       (includetext
                                       guardwhitespace
                                       height=0.6)
                                       ean8
                                       barcode


UPC-A



  Data
      11 or 12 digits

  Options
       ______________________________________
      |Option_____|Feature___________________|
      |includetext|Enable_human_readable_text|


  Notes
      If just 11 digits are entered then the check digit is calculated
      automatically

                                       Figure
                                       3:
                                       (78858101497)
                                       (includetext)
                                       upca
                                       barcode


UPC-E



  Data
      7 or 8 digits

  Options
       ______________________________________
      |Option_____|Feature___________________|
      |includetext|Enable_human_readable_text|


  Notes
      If just 7 digits are entered then the check digit is calculated
      automatically

                                       Figure
                                       4:
                                       (0123456)
                                       (includetext)
                                       upce
                                       barcode


EAN-5



  Data
      5 digits

  Options
       ______________________________________
      |Option_____|Feature___________________|
      |includetext|Enable_human_readable_text|


                                       Figure
                                       5:
                                       (90200)
                                       (includetext
                                       guardwhitespace)
                                       ean5
                                       barcode


EAN-2



  Data
      2 digits

  Options
       ______________________________________
      |Option_____|Feature___________________|
      |includetext|Enable_human_readable_text|


                                       Figure
                                       6:
                                       (38)
                                       (includetext
                                       guardwhitespace)
                                       ean2
                                       barcode


ISBN



  Data
      9 or 10 digits seperated appropriately with dashes

  Options
       ______________________________________
      |Option_____|Feature___________________|
      |includetext|Enable_human_readable_text|


  Notes
      If just 9 digits are entered then the human readable ISBN check digit is
      calculated automatically

                                       Figure
                                       7:
                                       (1-
                                       58880-
                                       149)
                                       (includetext)
                                       isbn
                                       barcode


Code-39



  Data
      Variable number of characters, digits and any of the symbols -. *$/+%.

  Options
       ___________________________________________________
      |Option____________|Feature_________________________|
      |includecheck______|Enable_check_digit______________|
      |includetext_______|Enable_human_readable_text______|
      |includecheckintext|Make_check_digit_visible_in_text|


                                       Figure
                                       8:
                                       (CODE-
                                       39)
                                       (includecheck
                                       includetext)
                                       code39
                                       barcode


Code-128 and UCC/EAN-128



  Data
      Variable number of ASCII characters and special funtion symbols, starting
      with the approriate start character for the initial character set. UCC/
      EAN-128s must have a manditory FNC 1 symbol immediately following the
      start character.

  Options
       ___________________________________________________
      |Option____________|Feature_________________________|
      |includetext_______|Enable_human_readable_text______|
      |includecheckintext|Make_check_digit_visible_in_text|


  Notes
      Any non-printable character can be entered via its escaped ordinal value,
      for example ^070 for ACK and ^102 for FNC 1. Since a caret symbol serves
      as an escape character it must be escaped as ^062 if used in the data.
      The check character is always added automatically.

                                       Figure
                                       9:
                                       (^104^102Count^0991234^101!)
                                       (includetext)
                                       code128
                                       barcode


Rationalized Codabar



  Data
      Variable number of digits and any of the symbols -$:/.+ABCD.

  Options
       ___________________________________________________
      |Option____________|Feature_________________________|
      |includecheck______|Enable_check_digit______________|
      |includetext_______|Enable_human_readable_text______|
      |includecheckintext|Make_check_digit_visible_in_text|


                                       Figure
                                       10:
                                       (0123456789)
                                       (includetext)
                                       rationalizedCodabar
                                       barcode


Interleaved 2 of 5 and ITF-14



  Data
      Variable number of digits. An ITF-14 is 14 characters and does not have a
      check digit.

  Options
       ___________________________________________________
      |Option____________|Feature_________________________|
      |includecheck______|Enable_check_digit______________|
      |includetext_______|Enable_human_readable_text______|
      |includecheckintext|Make_check_digit_visible_in_text|


  Notes
      The data may be automatically prefixed with 0 to make the data, including
      optional check digit, of even length.

                                       Figure
                                       11:
                                       (05012345678900)
                                       (includecheck
                                       height=0.7)
                                       interleaved2of5
                                       barcode


Code 2 of 5



  Data
      Variable number of digits

  Options
       ______________________________________
      |Option_____|Feature___________________|
      |includetext|Enable_human_readable_text|


                                       Figure
                                       12:
                                       (0123456789)
                                       (includetext
                                       textpos=75
                                       textfont=Helvetica
                                       textsize=16)
                                       code2of5
                                       barcode


Postnet



  Data
      Variable number digits

  Options
       ___________________________________________________________
      |Option____________|Feature_________________________________|
      |includetext_______|Enable_human_readable_text______________|
      |includecheckintext|Make_the_check_digit_visible_in_the_text|


  Notes
      Check digit is always added automatically

                                       Figure
                                       13:
                                       (01234567)
                                       (includetext
                                       textpos=-
                                       10
                                       textfont=Arial
                                       textsize=10)
                                       postnet
                                       barcode


Royal Mail



  Data
      Variable number digits and capital letters

  Options
       ___________________________________________________________
      |Option____________|Feature_________________________________|
      |includetext_______|Enable_human_readable_text______________|
      |includecheckintext|Make_the_check_digit_visible_in_the_text|


  Notes
      Check digit is always added automatically

                                       Figure
                                       14:
                                       (LE28HS9Z)
                                       (includetext)
                                       royalmail
                                       barcode


MSI



  Data
      Variable number digits

  Options
       _______________________________________________________
      |Option____________|Feature_____________________________|
      |includecheck______|Enable_check_digit__________________|
      |includetext_______|Enable_human_readable_text__________|
      |includecheckintext|Make_check_digit_visible_in_the_text|


                                       Figure
                                       15:
                                       (0123456789)
                                       (includecheck
                                       includetext)
                                       msi
                                       barcode


Plessey



  Data
      Variable number of hexadecimal characters

  Options
       ____________________________________________________________
      |Option____________|Feature__________________________________|
      |includetext_______|Enable_human_readable_text_______________|
      |includecheckintext|Make_the_check_digits_visible_in_the_text|


  Notes
      Check digits are always added automatically.

                                       Figure
                                       16:
                                       (012345ABCDEF)
                                       (includetext)
                                       plessey
                                       barcode




License

Copyright 2004 Terry Burton
Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
of the Software, and to permit persons to whom the Software is furnished to do
so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
The software is provided "as is", without warranty of any kind, express or
implied, including but not limited to the warranties of merchantability,
fitness for a particular purpose and noninfringement. In no event shall the
authors or copyright holders be liable for any claim, damages or other
liability, whether in an action of contract, tort or otherwise, arising from,
out of or in connection with the software or the use or other dealings in the
software.

-------------------------------------------------------------------------------

Footnotes



  ... language1
      The PostScript Language Tutorial and Cookbook (a.k.a. the Blue Book),
      which is freely available online, serves as both a useful tutorial and
      reference manual to the language.

  ... symbology2
      By symbology we mean an accepted standard for representation of data as a
      barcode


-------------------------------------------------------------------------------
     http://www.terryburton.co.uk/barcodewriter