How Barcodes are Read
Basically, a barcode consists of parallel adjacent lines of varying thicknesses and spaces which can be decoded by a barcode reader. This occurs by scanning a light source across the barcode and measuring the intensity of light reflected back by the white spaces. The pattern of reflected light is detected through a photodiode, producing an electronic signal that matches the barcode pattern. Then, the signal is decoded back to its original form via electronic circuits. Let’s take a closer look at how different types of barcode scanners read barcodes.
There are four different types of barcode readers available on the market today, and each uses a slightly different message for reading and decoding barcodes.
Laser scanners use a laser beam as their light source and employ a reciprocating mirror or rotating prism to scan the laser beam back and forth across the barcode. A photo diode is used to measure the intensity of the light reflected back from the white spaces in the barcode. The light is then emitted by the reader and turned into a specific frequency via the photo diode.
Pen readers use a light source and an adjacent photo diode on the tip of the pen or wand. To read the barcode, the tip is dragged across the bars in an even motion. The intensity of the light reflected back from the light source is measured by the photo diode, which then generates a waveform used to measure the widths of the bars and spaces in the barcode. Dark bars absorb light, while white space reflects it, producing a voltage waveform generated by the photo diode that’s an exact duplicate of the bar and space pattern in the barcode. The waveform is then decoded by the reader.
CCD (Charge Coupled Device) Readers
CCD readers use hundreds of light sensors in a row formation that act as a single photo diode, measuring the intensity of the light in front of them. Each individual light sensor in the row uses a voltage pattern identical to the pattern in the barcode an is generated in the reader by measuring the voltages across each sensor in a row. Unlike pen or laser scanners, CCD readers measure the amount of ambient light emitted from the barcode.
Camera Based Readers
Camera based readers use a small video camera to capture the barcode’s image. The reader then decodes the barcode via advanced digital image processing techniques. Although Camera based readers use similar technology as a CCD barcode reader, video cameras employ hundreds of rows of sensors arranged into a two dimensional array so that they can generate an image.
Essentially, in order to properly read a barcode, an adequate print contrast between the white spaces and dark bars is of the utmost importance. It is also helpful to have sharp bar edges and adequate quiet zones at either end of the symbol.
If you’re interested in learning more on barcode scanning, click here.