Barcode Basics

Barcode design and implementation are governed by standards, specific for each type of barcode, which are summarized below:

Note that barcode standards concern themselves primarily with laser scanners that have specially designed optics. Image based barcodes often do not fully comply with the standard requirements, neverheless, ClearImage COM is able to recognize them.
Barcodes are comprised of a set of black lines (bars) separated by white areas (spaces). The particular symbology standard specifies possible sizes of bars and spaces. In some cases, the standard may specify the distances from one bar to the next and from one space to the next. In all cases, these sizes and distances are expressed in terms of multiples of the smallest dimensional unit, called a module. The module is the smallest width and/or length of a space, bar or dot in the barcode symbol. Linear, 1D Barcode standards also specify the minimum height of the bars.
Each character of encoded data is represented by set of bars and spaces of of varying width. The standard specifies how many bars and spaces encode a character. Typically total number of space and bar modules encoding a character is fixed for given code type. Sometimes, the name of barcode reflects these numbers, as in Code 93, which contains 3 bars and 3 spaces. The combined width of all bars and spaces is 9 modules.
Bars and spaces at the beginning and at the end of the barcode symbol, called start/stop characters, are added to identify a barcode of a specific type.
Format characters might be included in the symbol. They specify the character set to be used for converting the encoded data back to the original text. This is clearly necessary when dealing with non english languages.
Error detection and correction bits may be added to the symbol. One example of such data is a checksum. The standard specifies the checksum calculation algorithm.
White areas surrounding the barcode symbol are called quiet zones and separate the symbol from the rest of the image. The standards specify the minimum size of the quiet zones.

"The Bar Code Book" by Roger C. Palmer contains just about everything you every wanted to know about barcodes, application information and selection considerations. Also look at the Inlite Research Web Site under Technology (for additional details on barcode standards and appearance) and the Support/Resource seciont for additional links and information.