Bar Codes

Contents

Introduction to Bar Codes. 1

Hardware bar code readers. 1

Choosing a bar Code. 1

Code 128. 1

RM4SCC. 1

QR. 1

Testing your Barcodes. 1

Barcode Clean Up. 1

Barcode Integrity (Ensuring it works). 1

Rasterizing (Convert to bitmap). 1

Neighbouring Print. 1

Aspect. 1

Rotation. 1

 

Introduction to Bar Codes

Many business applications often have to produce bar codes or maybe could benefit from them. Bar codes are typically printed onto physical paper work so they can be scanned at some point so the human operator does not have to worry about “keying in” a particular reference code. Big advantage being improvements on speed and input error.

Bar codes generally fit into these groups, based on their structure:

·         1D           Traditional Bar codes, like on a can of beans.

·         2D           Square, High density bar codes like QR.

·         3D           Square with Colour, not implemented as not commonly used.

If you just want to encode a simple reference number then 1D is the way to go. If you want to ‘store’ data in the bar code the 2D is for you.

Hardware bar code readers

These days you can get pretty good 1D and 2D bar code readers for around £20 all be it on the slow boat from China.

Many moons ago the only bar code reader you could get for £20 was a 1D CCD/LED scanner, these performed awfully, you don’t really see them anymore. Avoid them, they have a row of around 6 LEDs in the front of them.

The more you pay the better performance you should, in theory, achieve. I haven’t tested any expensive scanners of recent so I’m not going to comment any further on them.

The 1D and 2D scanners use completely different technology and each have their pros and cons:

·         1D – Uses a laser, only scans 1D, good scan distance and ambient light performance, will not scan from computer screen

·         2D – Uses a camera, scans 1D and 2D, scan distance performance not so good, will scan from computer screen

The decision is pretty simple; for shop floor where only 1D is required use a laser based 1D only scanner, for everything else use a camera based 2D scanner.

The camera 2D scanner is great for the developer because it scans everything and you can even point it at your screen without having to print anything out.

From the user’s PC perspective the scanner behaves like a USB keyboard (old PS/2 has a pass-through). The user scans a bar code and it is as if they just typed in whatever is encoded in the bar code. If they are entering data into a form then the input field on screen must have focus (just like with the keyboard when you enter data).

Having said that many scanners will allow you to configure them to work over a serial port so you can create an application that receives data directly from them independently of keyboard input, which may give a more robust UI experience (no need to worry about a textbox having focus).

Barcode readers are often configured using a set of magic bar codes that are in the manual. Things like which bar code types are accepted and whether or not it automatically puts new lines on the end (hits enter after the data). Normally the default is fine.

Choosing a bar Code

There are 2 native built in barcode types Code 128 & RM4SCC.

All other barcode types are handled by ZXing.net, so the “Spludlow.ZXing” assembly needs building and present in Applications.txt on the host that will print the document. This will give you the following bar codes:

Bar Code ID	Full Name	Contents	Usage
Built in
Code128	Code 128	Same as “Code128B”	General Purpose (defaults B)
Code128A	Code 128 set A	ASCII 32-95 (space to underscore) and ASCII control	If you need ASCII control
Code128B	Code 128 set B	ASCII all printable characters 32-127 (space to tilde and DEL)	All the ASCII printable characters
Code128C	Code 128 set C	Digits	Digits encoded in pairs for higher density
RM4SCC	Royal Mail 4-State Customer Code	Alphanumeric	UK Post codes
ZXing 1D
CODABAR	Codabar	Digits and: - $	General Purpose
CODE_39	Code 39	Alphanumeric, space and: - . $ / + %	General Purpose
CODE_93	Code 93	Alphanumeric, space and: - . $ / + %	Higher density and security enhancement to Code 39
CODE_128	Code 128	ASCII or Digits	General Purpose
EAN_8	EAN-8	7 Digits	European Article Number
EAN_13	EAN-13	12 Digits	European Article Number
ITF	ITF	Digits	Interleaved 2 of 5 ITF-14
UPC_A	UPC-A	11 Digits	Goods identification
UPC_E	UPC-E	7 Digits	Goods identification
MSI	MSI	Digits (0-9)	Modified Plessey
PLESSEY	Plessey Code	Hex (0-9 A-F)	Hexadecimal
ZXing 2D
AZTEC	Aztec Code	2D
DATA_MATRIX	Data Matrix	2D
PDF_417	PDF417	2D
QR_CODE	QR Code	2D
ZXing not Implemented
MAXICODE
RSS_14
RSS_EXPANDED
All_1D
UPC_EAN_EXTENSION
IMB

 

Run the method “Spludlow.Drawing.BarCode.TestSheet(filename)” to produce a code demo:

NOTE: If “Spludlow.ZXing” is not present then only the first 5 native codes will be printed. The filename can be .png or .jpg if you want .pdf then “Spludlow.Drawing.PDF” must be present.

Code 128

Code 128 is well supported and covers many characters, if you require a 2D code then consider it first.

Set C gives double density when using digits only, make sure you zero pad to an even length (native encoder will automatically do this), single digits are not encode-able. (“0123” rather than “123”).

Some additional built in functionality is also provided like changing sets within the barcode and encoding further characters using “Function 4”. I doubt anyone would use this in practice.

RM4SCC

Used by the Royal Mail. This bar code is the lowest tech 2D barcode; of its equally spaced bars and gaps there are 4 shapes of bar, so standard 1D barcode readers will not read these.

QR

If you require 2D.

Testing your Barcodes

Get a 2D scanner for £20. If you are waiting for the slow boat from China you can use “Spludlow.Drawing.ZXings.Decode(filename)” provided “Spludlow.ZXing” is present.

Other than then the look on the web for online decoders. Not many things decode RM4SCC I did find a web page that did this.

Barcode Clean Up

The framework bar code data in is cleaned up before turning into rectangles. All whitespace around the edges will be removed and rectangles will be joined up where possible.

Here you can see the rectangle simplification in practice applied to the ZXing output matrix:

Trimming whitespace simplifies page layout, the barcode sits in the specified rectangle. You may have to add whitespace yourself for certain barcode types, basically put a white rectangle that is slightly bigger behind the barcode.

Simplifying the rectangles will also benefit the barcode:

·         Better bitmap rendering with antialiasing (you can see faint white lines between individual rectangles)

·         Smaller PDF size (The all on one sheet test sheet was 14K compared to 74K)

·         Simpler vectors are better for incorporating into an artwork design

Barcode Integrity (Ensuring it works)

What you don’t want is your barcodes not scanning, either from paperwork printed by your system or a PDF that the end user prints out.

Rasterizing (Convert to bitmap)

Problems can arise when the barcode is rasterized (converted from descriptions of rectangles into a bitmap). There will be a point where barcode density is too great for the available pixels, antialiasing can also impair the barcode further.

As the framework uses vectors internally and customer printed documents are usually PDF then rasterization is performed at the last stage, physical printing, the bitmap should be printed at the printers native resolution (in theory at least 300dpi). Antialiasing may occur within the printer but the resolution is sufficiently high to make this irrelevant. So by default everything is fine.

What you should be aware of is supplying barcodes in bitmap formats. Even if they are spot on pixel perfect bitmaps placed into a PDF, when they get printed the image may get scaled and distorted (fluffed up). To avoid this you could place higher resolution bitmaps in the PDF, but this will add to file size.

NOTE: In reality these problems aren’t as bad as I make out here, just be aware.

Neighbouring Print

Some barcodes have rules within their specifications for how much white space should be around the barcode, you should check this.

Aspect

1D bar codes can handle being stretched in either direction without ill effect (provided you maintain the resolution across the barcode).

2D bar codes are a bit fussier:

·         RM4SCC – bar width should give 20 to 24 bars per inch (this range should allow for post code lengths varying with a fixed width). Height around 10mm

·         PDF417 – Seems to cope with being stretched in each direction in tests I did, although nice to keep it looking like a boarding card. The spec says: Row height must be at least 3 times the minimum width

·         Square types (Aztec, Data Matrix, and QR) – Don’t like not being square, always keep the width and height equal.

Rotation

The framework allows you to rotate a bar code by 90 degrees. No other rotation angles are supported. Rasterizing barcodes at non-square angles will lead to jagged edges making reading difficult for the scanner and should never be done. NEVER!