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('',); 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