Printing 100% compliant barcodes from any printer to any label or
document will ensure perfect readability. With good quality label printers
with built-in barcode support this is usually possible as long as you
carefully follow the manufacturer's quality control directions. But good
thermal printers can cost several thousand dollars and are only designed
for label printing. What about printing from general purpose printers,
such as laser printers? In this case the software used is critical to
guarantee perfect barcodes.
The guidelines below are based on the
industry standard recommendations of the Uniform Code Council for EAN/UPC
symbols but the concepts apply equally well to all barcode
symbologies.
As a user it is important to understand these concepts
in selecting the best hardware and software for barcode printing.
Thermal Transfer Bar Code Label Printers
These are commonly used printers for barcode labeling. It is most
important with this type of printer to make sure that you follow the
manufacturer’s recommendations for setting up the printer and testing the
bar codes. Direct thermal and thermal transfer printers require specific
settings for best results depending on the combination of label and ribbon
materials. The manufacturer will supply the directions for the correct
adjustment for your printer type.
It is also very important to
verify bar codes using an ANSI based verifier. This should be done after
any change in the label material or any change in the printer or it
settings. It should also be done or a regular basis to ensure quality is
maintained and when printing a long run.
To maintain the quality of
printed bar codes the manufacturer’s directions for cleaning the print
head and guide surfaces should be followed. It will also be necessary to
replace the thermal printhead eventually as these wear out. When this
happens the bar codes will no longer be readable as one or more of the dot
elements will not heat properly.
It is so important to verify
printed symbols on a regular basis that some thermal printers can be
equipped with on-line verifiers.
With thermal printers the quality
of the label design software you use will not effect the quality of the
printed bar codes.This is because the software is just sending a command
to print a bar code - a command that triggers the printer’s internal
software to actually generate and print the correct bar code.
General Purpose Printers
General purpose printers, especially laser printers, are excellent for
producing bar code labels on sheets of pre-cut labels (such as "Avery"
labels) or on continuous feed labels. Obviously, for anyone needing
extremely high quantities of bar codes on a daily basis thermal transfer
printers with their high speed would be better, but for many users general
purpose printers, especially laser printers, are preferably.
Laser
printers are also perfect for creating bar codes on documents, such as
medical and legal records, coded "mail-merge" letters, etc. Imagesetters,
such as Linotronic printers, are used to create high quality, 2540+ dpi,
film positives and negatives for commercial printing.
With general
purpose printers, including laser, desk top, ink jet, ion deposition, dot
matrix and imagesetter, the software used is critical to ensuring readable
symbols.
"There is a wide variety of software packages for creating symbols
using general purpose printers. Unfortunately, many of these packages are
capable of producing symbols with totally unacceptable quality."
UCC Guidelines for Producing Quality Symbols, April 1998
The software used should beable to satisfy the following
requirements:
Dots Per Bar Width
When specifying the narrow bar (module) width the user should be able
to specify an integer multiple of the printer dot width. This is best
explained with an example. For a 600dpi printer the actual dot width is
1/609.6* = 0.00164". The module width should be specified as an integer
multiple of printer dots, i.e.
8 dots per module gives a width of
13.12 Mils and a Magnification Factor of 100.95%
7 dots per module
gives a width of 11.48 Mils and a Magnification Factor of 88.33%.
(*A 600 dpi printer with an actual 609.6 dpi)
Module (bar) width
defined as 8 printer dots or 13.12 Mils or a Magnification Factor of
100.95%
Module (bar) width defined as 13 Mils or a Magnification Factor of
100%. This is not an Integer number of printer dots. Rounding errors could
occur when printing.
The easiest way to achieve the correct module width for your printer is
to have software that:
i. Allows you to specify the target printer resolution or finds
the resolution for you for the printer you have selected.
ii. Then allows you to specify the module width in "printer
dots" (it would already know the "dots per inch"). You would select the
number of printer dots that most closely matches the Magnification Factor,
or module width in Mils, that you desire. If you wanted 100% magnification
an "8 printer dot" width for a 600 dpi printer would be the closest.
Bar Width Reduction
The software you select also needs to have an option for "Bar Width
Reduction." This is important when printing to any printer that has "dot
spread". This includes ink jet printers and "wet ink" printers (but not
laser printers). For these printers one dot of bar width reduction is
recommended per bar width. For instance for a 300 dpi ink jet printer with
a module width of 13.12 Mils (4 printer dots per module width) Bar Width
Reduction of one dot would be 3.28 Mils or 25%.
Bar Width Reduction
is also required when bar codes are going to be printed on a commercial
(wet ink) press. In this case the artwork containing the bar code is
usually output on film from an Imagesetter. Imagesetters have resolutions
of 2400+ dpi so the required bar width reduction can be specified exactly.
The actual amount of reduction required is determined by the paper and ink
used and this should be specified by the printer. If printing to a smooth
hard surface, such as a glass bottle, Bar Width Gain may be required.
Again, you should consult your commercial printer for his recommendations
before generating the bar codes.
Bar Code Graphic Type
There are 3 main types of bar code software
products:
1 . Bar Code Fonts
2 . Bit-map (Raster) Bar
Code Generators
3 . Vector Bar Code Generators
Each is
discussed below:
1 . Bar Code Fonts
"Bar code fonts have been known to create EAN/UPC symbols with
serious design defects. The problems may be caused by the design of
the font, an operator input, or a combination of
both."
UCC Guidelines for Providers of
EAN/UPC Symbol Design Software, July 1997.
"Extreme caution should be used when producing EAN/UPC symbols
with bar code fonts."
The Uniform Code
Council does not recommend the use of fonts. As problems it cites in
particular the ability to manipulate the size of individual characters
(distortion), spacing between the characters (kerning) and the
possibility of font or resolution substitution at the output stage.
However there are many other problems with bar code fonts. The user
cannot specify the module (bar) width exactly in printer dots. Fonts do
not support Bar Width Reduction. Nor do they support many of the
features specific to bar code symbols such as Bearer Bars, Quiet Zones,
independent symbol height and module (bar) width specification, symbol
rotation and support for binary data (including ACSII nulls in Code 128,
Code 39, Code 93 and PDF 417). In addition, most fonts do not
automatically calculate and add check digits and other security features
to bar codes.
2 . Bit-map Bar Code Generators
A bit map image is device dependent. This means a bitmap of a one
inch square to be printed at 300 dpi would be 300 pixels across by 300
pixels down. If a bar code designed to print one inch square on a 300
dpi printer were printed instead on a 600 dpi printer the resulting bar
code would be ?inch x ?inch. This is because there would only be 300x300
pixels in the image instead of 600x600.
The other problem with
bit-maps images is their size. If you are printing to a 200 dpi printer
a one inch square would contain 200 x 200 =40,000 bits of data. This is
bad enough but to a higher resolution printer, such as a common 600 dpi
printer it would be 360,000 bits of data (and 6.5 million bits of data
for a 2540 dpi Imagesetter!!). These huge files not only use large
amounts of computer memory they also print extremely slowly.
3 . Vector Bar Code Generators
Vector graphics are perfect for defining bar code images. A vector
image is a set of drawing commands that precisely defines the edges of
each bar and specifies how to fill in the area created within the
defined edges.
Vector images are completely device independent as
they are a set of precise commands instead of a collection of dots. A 1"
x 1" box will print 1" by 1" on a 100, 600 or 2540 dpi printer! When a
vector image is sent to a general printer the printer’s software
converts it to a raster image so that it can print it. The Raster Image
Processor in the Printer converts the precise path commands in the
vector graphic into a series of pixels. Hence the exact measurements of
the image are influenced by the resolution of the printer. A higher
resolution printer will be able to more precisely match the exact
measurements of the vector graphic. A lower resolution printer will need
to round the dimensions to the nearest integer number of printer dots.
This is why it is so important, especially in printers of 600 dpi or
less, to specify the module (bar) width in integers of printer dots (see
part 1 above).
Vector bar code graphics are also much smaller
than other bar code graphics so they print many, many times faster. For
instance, a typical 1" high UPC code at 100% magnification would create
a 149 KB bitmap for a 600 dpi printer. A Windows Metafile (WMF) vector
graphic of this bar code would be 2 KB and an Encapsulated Postscript
(EPS) vector graphic with a TIFF preview would be 48 KB and 29 KB
without the TIFF preview. Windows Metafiles (WMF) are the best graphic
format for bar codes in Windows and EPS in the Mac (Macs do not support
WMF graphics).
Once the bar code is created by any bar code
software it should not be resized, scaled or stretched. If the bar code
is to be transferred to a second party, information, such as the minimum
printer resolution for that bar width, should be
communicated.
Bar Code Verification
As with Thermal Transfer printers, it is important to test the output
from General Purpose printers using a bar code verifier. The UCC
recommends using the test symbols:
0 12345 01234 1
6 78912
56789 0
If they fall below a grade B check that you have specified
a Magnification Factor (or module width) that corresponds to an integer
number of printer dots per module (bar) width. Bar Width Reduction may
also be required as discussed above.
If the user does not have a
bar code verifier he can submit the bar codes to a qualified testing
organization. If nothing else, at least they should be tested with a bar
code reader.
Further Information
For the complete, in-depth, guidelines please refer to the following
Uniform Code Council documents
- UCC Guidelines for Producing Quality Symbols, April 1998
- Guidelines for providers of EAN/UPC Symbol Design Software, July
1997
- UCC Technical Bulletin #1, April 1997
You can download a FREE demo for TAL’s bar code generating software, B-Coder Pro and the ActiveX
control. Use this to create bar codes in any size and any graphic
format. Take the recommendations above to create bar codes as WMF Vector
graphics and define the module (bar) width in "Printer Dots". B-Coder Pro
automates bar code production on labels and documents from MS Word,
Access, PageMaker and other Windows application programs.
A FREE
demo also available for the TAL
Bar Code DLLs. These programmers’ tools allow developers to add high
resolution, completely device-independent, bar code printing capability to
their custom applications, royalty free! As with B-Coder Pro, the DLLs
fully comply with industry recommendations to print 100% compliant bar
codes.
B-Coder
Pro
Bar
Code DLLs
TAL
ActiveX Contol
Bar
Code Basics
How
a Bar Code Reader Works
Bar
Code Symbology Descriptions
|
