Modulation compares the least black-to-white area of the symbol to the greatest difference between the black and white elements. This is measured and then graded from 4 to 0.Ī barcode should be evenly black and white across its whole area. Axial non-uniformity is a measure of how out of square the barcode is when checked against its horizontal and vertical axes. This is measured in percentage terms, and the percentages are converted into five different bands – 4,3,2,1, or 0.Īll matrix 2D symbols should comprise perfectly square, and evenly spaced, elements. The quiet zones will normally be the lightest areas. The symbol contrast is the difference between the darkest and lightest areas of the barcode. If the barcode cannot be decoded, the grade is 0.0. If there is a valid decode, the grade is 4.0.
2D BARCODE VERIFICATION
This is the first step in the verification and applies the reference decode algorithm - the set of rules defined by ISO/IEC for decoding the symbol - to the image. The seven parameters are all briefly explained below: Where N.0 is the grade, aa is the aperture refence number, which refers to the diameter of the aperture measured in 1/1000s of an inch, www is the wavelength of light measured in nm, and 30 or 45 or 90 is the angle of the incident light used to illuminate the barcode. The grade is then reported with the details of the aperture, the light, and the angle of illumination as follows: The parameter with the lowest grade becomes the overall grade for the 2D symbol. The seven parameters are each measured, and the measurements converted into grades 4,3,2,1 or 0, with 4 being best, and 0 being a failure. Unlike linear barcode verifiers, only one image is used. This image is then analysed using a known sampling area (defined as the aperture reference) to measure seven different aspects, or parameters, of the symbol. All barcode verifiers must use a standardised lighting configuration, with light of a specified wavelength, to take an image of the barcode.
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