PSOFT BARCODE PORTAL.

Symbology standard must contain:

• A definition of the width of the bars and the spaces
• A method to define each character that is encodable (whether numeric only or full ASCII)
• The start and stop characters
• Any check character support built in
• Any free space needed around the symbology to allow for a clean decode

Continous barcode, Discrete barcode.

• Continuos barcode is barcode, where last module is nearest to next char. Between coded chars isn't space, but this space is part of coded char. Last char ends with space and next char begin with bar.
• Discrete barcode must have between two chars some space, because char start and end with bar, code must have between two chars one or more space.

Module.

Quiet zone.

Check char (checksum).

• Modulo 10 - used in all EAN,ISBN,ISSN,ISMN,UPC barcodes
• Modulo 11 - used in Code 11
• Modulo 107 - used in Telepen
• Good is Reed Solomon error correction - used in 2D barcodes. Added some redundantion data to barcode for error correction. You can have only part of barcode, destroyed barcode and error correction solve your problem.
• Error correction mode can be set from 5% to 95%, highest error correction level make of course smallest coded data size, but make this barcode very secure. 5% level is good, but you make barcode only with small damage, 95% is very good after damage, but more information is error correction as data :-(

Add-on 2 or 5 digits

Element.

• For 1D barcodes (EAN,UPC,Code39,Code93,...) is one element one pixels. Bit "1" is black line, bit "0" is white space. If you need largest barcode (on laser printer is one pixel very small :-) ), you can increase all element, but good is all elements multiplicate with same coefficient. Barcodes have some printer tollerance, but some 30-40% is maximum. If single line is 10 pixels width, and simple space 11 pixels, this is good. But if simple space is in width 16 pixels, bad. Barcode unreadable.
• For 2D barcodes is width and height of element equal. And all 2D barcodes contain error correction algorithm for remove errors.

Error correction.

• See Check char. For 1D (linear) barcodes is used check char added after last coded char, before stop char. This char is compared with barcode scanner with all others characters, calculated and if not equal, barcode is bad. If yes, all is O.K. 1D barcodes have troubles with reading in 100.000-1.000.000 barcodes
• Better is 2D code, because there is more amount of data, uses better algoritms. To barcode are added some additional data for repair damaged data. This algorithms can correct 5-95% of damaged data. Error correction level user can set, but if better error correction level, smaller data can you code, because barcode include more error correction information. In 95% error level you need only 1/5 barcode and no problem with reading.

Start/Stop symbol.

• Start symbol is begin of barcode, only in 1D barcode. Before this symbol must be quiet zone. This indicate barcode symbology. After this symbol continues barcode text.
• Stop symbol is last symbol in barcode. Before this symbol can be checksum. After stop symbol must be quiet zone for easy reading of barcode, no images, lines, text.

Reed Solomon alghorithm.

• Reed-Solomon codes are block-based error correcting codes with a wide range of applications in digital communications and storage. Reed-Solomon codes are used to correct errors in many systems including:
• 
  
• Storage devices (including tape, Compact Disk, DVD, barcodes, etc)
• Wireless or mobile communications (including cellular telephones, microwave links, etc)
• Satellite communications
• Digital television / DVB
• High-speed modems such as ADSL, xDSL, etc.
• 
  
• Typical scheme: DATA -> REED-SOLOMON ENCODER -> TRANSMISSION (with errors, of course) -> REED SOLOMON DECODER-> DATA WITHOUT ERRORS (if possible), easy :-)
• 
  
• For barcode : Reed-Solomon error correction adds to barcode additional char. This chars is very good if barcode is damaged. Correct problems and barcode is good. Nice. But problem is in error correction level.
  5% error correction is small, only small part of barcode can be damaged. 95% is very good, but additional informations is large as coded data :-(, 50% this gold road...
• 
  
• Further reading : In this paper we have deliberately avoided discussing the theory and implementation of Reed-Solomon codes in detail. For more detail please see the following books:
• Wicker, "Error Control Systems for Digital Communication and Storage", Prentice-Hall 1995
• Lin and Costello, "Error Control Coding: Fundamentals and Applications", Prentice-Hall 1983
• Clark and Cain, "Error Correction Coding for Digital Communications", Plenum 1988
• Wilson, "Digital Modulation and Coding", Prentice-Hall 1996

Omni-directional, Bi-directional reading

• Easy - Omni-directional barcodes can be readed only from one side - from left to right. Barcode must begin with start character and ends with stop character.
• Bi-directional can be readed from left to right or from right to left. Start and stop code reader recognize. User not must barcode turn as needed. Barcode can start with stop character and stop with start character. This is good.

Human readable text.

Multirow symbology.

• PDF417
  • nice multirow barcode, very good error correction, 3 - 90 rows, all 128 ASCII codes, 8 bit binary data
  • Bi-directional encoding : Yes
  • error correction level 0 - 8
  • Additional options : MacroPDF417,MicroPDF417,...
  • Code16K - 2 - 16 rows, 5 chars per row, additionally up to 107 16-row symbols can be concatenated together to allow encoding of up to 8025 characters or 16050 digits.
  • Contain complete 128 ASCII character set

Advantages

• Easy input to computer or electronic cash register, reduce human errors and make input speed and easy.
• Easy print - for simple 1D code is dot printer good, but for better print is needed inkjet or laser printer
• 1D barcodes is very good for small codes- 10-15 chars, in large size have scanner troubles with reading, because difference between code and scanner is large or not all code is placed to scanner place.
• 2D barcodes is very capable - on 1 square inch no problem 1.000-2.000 chars
• Error correction - 1D barcodes includes checksum, indicate bad barcode. 2D barcodes uses error correction methods, eliminate destroyed or damaged barcodes, of course not in 100 %, but very good.
• Capacity of coded tetx in 2D barcode is very high - 2.000 - 7.000 bytes per 2-3 square inch
• 2D barcodes are very small in size, you can read this barcode from any position, no Omni-directional
• Multistacked symbols is good, because you can read from top to bottom, or from bottom to top, or random. Barcode is completed, because each row contain row number.
• 2D symbologies scan barcode as one entirety, no problem with rows and columns

Problems

• Matrix printer - for barcode no. Very small DPI, best is laser printer.
• 2D barcodes - not easy for implementation - you need laser printer, dot printer is lost :-(
• All barcodes 1D, Stacked,2D have some problem. InkJet printer is not good. If you ave hands on watter or if your document is on moisture, ink can be damaged, you have problem. On laser printer no.
• Error correction methods - not easy and more data needs
• 1D barcodes have smaller reliability as 2D, Human make error 1:300 (very bad), speed : small.
  1D barcode is readed bad in 1:1.000.000, 2D barcode around 1:100.000.000,speed is very good, try write 7.000 chars per 2-3 second :-)
• 1D barcodes must be readed using laser across all width barcode. If some line is not in laser, is problem
• 2D barcode isn't some world standard, you can code all info. Ean 13, Ean 8, UPC, ITF, RSS is standard, you have security, that two different goods on the world not have same barcode. This code allocate EAN, EAN Swerige EAN Slovakia

EAN COUNTRIES

CRC- Cyclic redundance code.

• Add one or two check digit to code
• Problem : add regundad information into message - longer barcode, but barcode id "power", for example in code PDF417 can be destroyed 90% of barcode picture and no problem ... readable. But some data is 10% from image, 90% is restoring data :-(
  But this CRC data is very usefull. Bad reading of barcode is about 1:100.000 in code 2/5,Code39.... to 100.000.000 with PDF417 barcode. This is very good.

2 DIMENSIONAL BARCODE

Printing techniques

Sample barcode - explain structure of barcode