Order Barcodes, Inc.

When the verifier is unable to find an appropriate number of bars and spaces, it reports an edge determination failure. IE The verifier must find 59 elements (30 bars and 29 spaces) for a UPC version A.

There are several reasons why a symbol may appear to have too many or too few elements. Excessive bar growth (ink spread) may cause the smaller spaces to become so narrow that the verifier can no longer see them.

The darkest bar must have a reflectance less than half of the background. This attribute is judged on a pass/fail basis. A failing grade for minimum reflectance will most often indicate that the bars should be printed darker or in a color that appears darker under red light.

The blackest possible bars printed on the whitest possible surface would have a 100% contrast. Practical printing of the UPC symbol on commercial materials results in less than 100% contrast. When the contrast becomes too low, scanners may have difficulty distinguishing the bars from the spaces; thus, higher contrast is desirable. Symbol contrast is graded A through F.

A low contrast grade indicates that either the bars are too light (not enough ink or ink not dark enough), the background is too dark, or both. Because the measurements are made with red light, it can be informative to visually inspect the symbol through a red transparency. When viewed in this fashion, the bars should appear to be much darker than the spaces. Generally speaking, the background (spaces) should be white or one of the warm colors (red, orange, yellow) and the bars should be black, brown, blue or green.

The attribute of minimum edge contrast is graded on a pass/fail basis. This parameter measures the smallest value for edge contrast in a scan reflectance profile between a bar and space.

Scanners and verifiers perceive the narrow spaces to be less white than the wide spaces. Similarly, but to a lesser extent, the narrow bars in a symbol look less black than the wide bars. This diminished intensity of narrow elements as compared to that of wide elements is called modulation.

The most probable reason for a low modulation grade is ink spread, which reduces the width and intensity of the single module spaces within the symbol.

Printing defects are of two types, voids and spots. Voids are light areas within the bars. Spots are dark areas in the spaces. Defects are undesirable because the scanner may become confused and think that a defect is an additional bar or space within the symbol. Symbols which yield profiles with poor defect grades can be examined with a good quality magnifier. The defects will be clearly visible. Usually, defects are voids that can be reduced or eliminated by increasing the amount of ink (or equivalent). Less often, excessive pigment or dirt may be deposited in the spaces, with resultant spots or inclusions.

Dimensional errors in printing a barcode symbol can make it difficult or impossible to scan. A verifier applies specific rules to the sequence of bars and spaces to decode them into a series of digits and guard bars. When the verifier is able to decode a symbol including its guard patterns, and when the check digit is consistent with the other preceding digits, the decode attribute passes with a grade of A; otherwise, the grade is F.

If all scan reflectance profiles for a symbol receive passing grades, but fail decode, the symbol is probably incorrectly encoded. It is reasonable to suspect that all or many of the symbols which were created by the same equipment in a similar time frame may also be defective. When only one out of several profiles fails to decode, the cause is usually a localized blemish in the symbol that can be spotted with a magnifier.

Decodability is a graded attribute that measures how near the scan reflectance profile is to approaching decode failure. Symbols which are printed to a high degree of dimensional accuracy will exhibit high decodability grades.

One common reason for low decodability grades is ragged, uneven bar edges. Another reason for low decodability is excessive bar growth (ink spread), which also tends to adversely affect modulation and edge determination. The creation of barcodes using an improperly designed graphics based software system is a likely cause of low decodability.

This is the first step in the verification process and involves applying the reference decode algorithm—a set of rules defined by ISO/IEC for decoding the symbol—to the captured image. If the symbol is successfully decoded, the grade for this parameter is 4.0. If decoding fails, the grade is 0.0.

Symbol contrast is the difference in reflectance between the darkest and lightest areas of the barcode, typically with the quiet zones being the lightest. This contrast is measured as a percentage, which is then converted into one of 41 discrete grading bands—ranging from 4.0, 3.9, and so on, down to 0.1 and 0.0.

Example of a 2D symbol with very poor symbol contrast:

All matrix-style 2D symbols should consist of perfectly square, evenly spaced elements. Axial non-uniformity measures how much the symbol deviates from being square when evaluated along its horizontal and vertical axes. This deviation is quantified and assigned a grade from 4.0 (perfect uniformity) down to 0.0 (unacceptable distortion).

This symbol has been seemingly stretched vertically, so will score less highly.

A barcode should exhibit consistent black and white contrast across its entire area. Modulation measures how the weakest transition between black and white compares to the strongest transition within the symbol. This variation in reflectance is evaluated and graded on a scale from 4.0 to 0.0.

The grey areas of this symbol will mean that it will not get the best grade for modulation.

Grid non-uniformity measures distortion in the symbol based on deviations from the expected positions of the centers of black and white modules. Any shift from the ideal grid alignment is quantified and graded on a scale from 4.0 to 0.0.

These two symbols are examples showing a high degree of grid non-uniformity.

All matrix-style 2D symbols include error correction characters, which can be used to reconstruct damaged or missing parts of the symbol. A perfect symbol requires no use of these characters and receives the highest grade of 4.0. This parameter is evaluated based on how much error correction is needed and is graded on a scale from 4.0 to 0.0.

The fixed patterns of a matrix-style 2D symbol help the scanner locate and interpret the barcode. If any of these patterns are damaged, the symbol becomes more difficult to read. This damage is measured and graded on a scale from 4.0 to 0.0.

For Data Matrix or GS1 DataMatrix symbols, the verifier examines the quiet zones, the L-shaped finder pattern, and the clock track (the dotted lines on the opposite two sides of the symbol). It calculates an average grade based on seven possible fixed pattern damage conditions.

Other 2D matrix symbols have different fixed pattern structures, and the verifier evaluates them according to their respective symbol specifications.

The grey areas of this symbol will mean that it will not get the best grade for modulation.

This parameter measures how the graphical features of the symbol have increased or decreased in size relative to their nominal dimensions. It evaluates both vertical and horizontal scaling, and the results are graded on a scale from 4.0 to 0.0.