The I/O menu shows all the commands that control a wide range of real-world reader behavior, including the enabling or disabling of messages about various reader states, the configuration of the LEDs, the enabling or disabling of messages about symbol quality, and the sending of signals to external systems such as conveyors and light stacks.
Command parameters can be changed directly from this menu.
The symbol grading features presented here are not intended to be, and should not be confused with, barcode verification. The individual parameter measurements in symbol grading are implemented in accordance with verification standards. However, calibration and other methodologies needed for compliant verification are not feasible in a reader configuration. Compliant verification is beyond the scope of this help topic, but reviewing a few topics can help in understanding how to deploy the features and functionality provided.
Verifiers are integrated systems designed to meet the rigorous demands of the verification specifications. To provide compliant verification, verifier systems are designed with specific features and functionality. In addition to specific requirements that are explicitly defined in the standards themselves, verifiers also incorporate general design features to eliminate sources of variability that can have adverse effects on the accuracy and repeatability of measurements. Readers are designed to provide maximum product flexibility for integration into systems that require reading for traceability. Key reader design specifications such as size, cost, read range, and read rate are a few factors that drive fundamental differences between verifier and reader designs. Understanding these tradeoffs in design can help users to optimize their reader systems to provide better accuracy and repeatability when grading.
V430-F readers provide no calibration features. The image captured by the reader is processed as-is and the intensity values of the image (0 – 255) are directly mapped to 0 – 100% reflectance grading purposes. Additionally, grading requires applying a synthetic aperture. A verifier normally applies an aperture using application standard requirements in combination with dimensional calibration. Without calibration the aperture needs to be specified by the user as a percentage of the nominal symbol dimension. Finally, some metrics in verification such as Minimum Reflectance in ISO 29158 are calculated using data that can only be provided through a calibration process and have no means of representation without such a process.
Key setup objectives when grading standard printed marks are listed below. Note that grading certain DPM marks with ISO 29158, such as dot peen marks, may require different and/or axial lighting to get an appropriate response from the symbol.
Select an optical configuration and distance that will achieve minimum pixel-per-element requirements for the target symbol. Select an optical configuration and illumination setup that achieves the requirements at a working distance greater than or equal to 6”. Working distances shorter than 6” can be used, although this introduces optical distortions that may impact performance of certain measurements.
Image the symbol as close to perpendicular as achievable in the application. Off-axis imaging introduces distortions that can be significant, even causing the symbol to fail to read during the grading process, resulting in all F grades.
Achieve and maintain the best possible focus on the symbol when grading. Small variations in focus can have substantial impacts on grading.
Provide even external illumination at or close to 45 degrees of incidence and disable the internal illuminating LEDs.
Illumination Distribution
Evenly-distributed illumination over the inspection area is a key component for accurate and repeatable grading. In general, ISO 15416 grading will be the most sensitive of the grading methods provided with regard to variation in illumination. This is because 1D symbols generally span a larger range in the field of view and many of the grading measurements that rely on absolute measurements can be impacted noticeably over that range. It is important to take care in achieving as flat a response as possible of the inspection area. Uneven illumination will not only impact the grade of a given symbol, but can also have a very large impact on repeatability of measurements. For example, a given symbol may achieve a different result in the center of the field of the view then it does near the edges or corner. Illumination providing a perfectly flat response will remove locational variance but this is not always possible. Care in symbol presentation, location, and consistency will have a significant impact on grading consistency.
Optical Distortion
Optical distortion of the symbol under test can also impact results. Optical distortion is introduced through a few different sources. The optics themselves will introduce non-linear distortions. These distortions will have a more significant impact on the symbol as the working distance is shortened. Lengthening the working distance reduces the variation in angle at which light traveling from the symbol enters the lensing system. Moving the symbol farther away also reduces the pixel per element resolution and changes illumination profiles, so care must be taken to optimize these parameters together. The symbol should be presented as close to 90 degrees to the imager as possible. Off-axis imaging will introduce distortion. Optical distortion mostly impacts 2D grading, particularly Axial and Grid Non-Uniformity, but will have cascading effects on other metrics.
Digital Resolution
A minimum digital resolution in the image is required to allow the software to have enough data to accurately measure the grading parameters. For ISO 15416 grading, 4 pixels per nominal symbol dimension are required. For ISO 15415 and ISO 29158 grading, 6 pixels per nominal symbol element are required. Under the highest-quality imaging, good performance can be seen down to 3 pixels for 1D and 5 pixels for 2D. This is system-dependent and requires optimal system focus and illumination. Not having enough resolution will impact repeatability and introduce overall degradation in dependent parameters.
Optical Resolution
Optical resolution is the ability of the optics to resolve detail in the image. High digital resolution of the symbol in the image does not equate to a high optical resolution. The system needs to resolve the detail of the image accurately. This requires making sure you are at optimal focus and that other considerations such as working distance and color of illumination have been evaluated to ensure they are not negatively impacting optical resolution in the system. When designing an optical setup you should evaluate and optimize to achieve the best possible modulation transfer function (MTF) for the imager. Poor optical resolution typically results in a degraded modulation score can have a cascading effect on other metrics.
The Grading Process
The three grading specifications described in this topic are independent of each other as an inspection process but are all dependent on the X-Mode decoder being properly set up to read the symbol type provided. The grading evaluation does not take place until a symbol has first been identified by the X-Mode decoder. Once a symbol supported by an enabled grading specification has been decoded by the decoder a separate grading evaluation will commence. Note this evaluation can potentially add significant processing time to the overall process and each specification requires independent evaluation. Furthermore, enabling any single parameter within a given specification requires the complete grading evaluation.
Overview
This section outlines the grading implementation for ISO 15416 available in the reader firmware. Please refer to the free AIM guide titled The Layman's Guide to ANSI, CEN, and ISO/IEC Linear Bar Code Print Quality Documents or to the relevant ISO specification documents for additional detail related to print quality.
Supported Symbologies
Minimum Resolution
Illumination and ISO 15416 Grading
The accuracy and consistency of ISO 15416 grading depends greatly upon the illumination in the field of view. ISO 15416 grading is evaluated by analyzing individual scan lines applied across the imaged symbol. These scan lines generate a signal called the scan reflectance profile which is the basis of the scan line grading methodology. This scan line grading methodology uses a fixed intensity threshold to determine whether the signal state represents a bar or space. In addition, this threshold is used as a reference for measuring the value for contrast, modulation, and defects. Simply reading a symbol with the X-Mode decoder can be achieved over a wide range of illumination profiles, but accurately grading a defect requires much tighter control of the environment. The level of accuracy required is not easily perceived by the human eye. To illustrate how variation that appears subtle to the eye can have a large impact on grading performance, consider the following image from a standard reader using internal illumination. The scan reflectance profile for the two line scans shown in the image is displayed to the right of the imaged symbols. The large symbol spanning the entire field of view shows dramatic differences in intensity. The spaces in the center of the symbol are providing 50% higher signal response then the quiet zones at either edge of the field of view. Similarly, the smaller symbol lower in the field of view provides a much lower overall response throughout its region. Scenarios like this will create low modulation scores and differences in defect scores depending on the physical location of the defect. If the symbol is moved within the field of view, it will receive a different score. It is recommended that external illumination is used and evaluated closely for response characteristics when performing ISO 15416 grading.
Figure 1: Uneven Illumination
Synthetic Aperture
The synthetic aperture is a process in ISO 15416 that is applied to the image when extracting the scan line profile for grading. The aperture is an averaging process using a circular region along the scan line shown below in Figure 2.
Figure 2: Scan Line Aperture
This averaging provides a generalization of the information in the image that is consistent with typical reading equipment acquisition techniques. Verification systems implement the aperture based on the physical dimension of the symbol under test and the application standard guidelines, such as GS1. In a reader that may have varying optical configurations and no calibration process, there is no means by which the process can determine the physical size of the symbol under inspection. For this reason the aperture is a configurable parameter as a percentage of the nominal dimension of the symbol under evaluation. The default value provides a general case that is close to most application standards. It is the user's responsibility to ensure this percentage matches the grading objectives. A representation of the effects of the aperture is provided in Figure 3. A larger aperture configuration creates more of an averaging effect that is less sensitive to defects but may lower modulation.
Overall, Scan, and Individual Parameter Grades
The overall grade is calculated in accordance with the process defined in ISO 15416. This is often misunderstood, so a review is provided here. The overall grade is an average of the individual scan grades that are applied over the inspection region. The individual scan grades are not provided by the reader but are calculated internally. These individual scan grades are the lowest grade of any single parameter grade evaluated in that particular scan line or 0 / F if the scan line evaluation fails the edge determination or quiet zone requirements. The individual parameter grades that are provided by the reader are averages of the individual parameters grades from each scan evaluated. These individual average parameter grades are not themselves part of the overall grade calculation but can be helpful for diagnosing the cause of declining overall grades. This creates circumstances in which the overall grade can be lower than the lowest average grade, particularly when there are degrading features in the symbol from different parameters.
Aperture
This determines the size of aperture to use for grading configured as a percentage of the nominal narrow element width for the symbol under evaluation. For example, if you have a 13 mil UPC symbol and you wish to grade using a 6 mil aperture you would configure the aperture to 46% (6/13 = 0.46).
ISO 15416 Grading Serial Output
Each grade metric can be individually enabled for serial output. These outputs can be in one of three different formats configured by the global quality output mode parameter. The mode can be configured as a letter grade A-F, the actual measured metric values (0 – 100), or as a normalized grade value score where the grade A-F is mapped from 0-100. The enabled outputs are appended to the symbol data with the grading separator. They are appended in their order of appearance in the grade metric section.
ISO 15416 Grading Logic Output and Threshold 1 – 3
Each of the three logic outputs available can be configured and driven by each of the individual grade metrics. Each output has a corresponding enable and threshold field for each metric used to control assertion of the output when the grade drops below the threshold value.
Overall Grade
The Overall Grade is calculated in accordance with the ISO 15416 specification. The Overall Grade is the average of the individual scan line grades applied to the symbol. The individual scan line grades are the lowest individual parameter grade seen during the individual scan. These scan grades are not available for output. For additional detail, see Overall, Scan, and Individual Parameter Grades earlier in this help topic.
Edge Determination
The Edge Determination check is done on each scan to ensure that element widths can be properly determined. Failing Edge Determination can occur with an uneven reflectance profile or with different types of damage. A failed Edge Determination scan results immediately as a failed decode scan.
Decode
Decode is calculated and graded for each scan and provided for the overall grade calculation in accordance with the ISO 15416 specification. The parameter grade and value provided for output is an average value for each measured scan over the entire symbol.
Symbol Contrast
Symbol Contrast measurements assume 8-bit 0 – 255 intensity in the captured image correlate directly to 0 – 100% reflectance. Symbol Contrast is calculated and graded for each scan and provided for the overall grade calculation in accordance with the ISO 15416 specification. The parameter grade and value provided for output is an average value for each measured scan over the entire symbol.
Minimum Reflectance
Minimum Reflectance is a measurement that, if failing, can indicate that bars are not providing adequate response difference from the substrate, which may cause readability issues. Envision very light gray bars on a white background versus very dark bars on a grey background. Both symbols are low contrast but the latter has a better Minimum Reflectance score. Small relative changes to in the light grey bars can more easily turn into errors against a bright background than small relative changes in a very dark bar against a gray background. Minimum Reflectance is calculated and graded for each scan and provided for the overall grade calculation in accordance with the ISO 15416 specification. The Minimum Reflectance parameter grade and value provided for output is an average value for each measured scan over the entire symbol.
Minimum Edge Contrast
Minimum Edge Contrast measurements assume 8-bit 0 – 255 intensity in the captured image correlate directly to 0 – 100% reflectance. Minimum Edge Contrast is an absolute measurement that ensures each element edge within the symbol achieves a minimum value. Uneven thermal or ink transfer, or printing on an inconsistent or uneven substrate, can result in areas where the edge of a bar is difficult to identify. The Minimum Edge Contrast is calculated and graded for each scan and provided for the overall grade calculation in accordance with the ISO 15416 specification. The parameter grade and value provided for output is an average value for each measured scan over the entire symbol.
Modulation
Modulation is a relative measure of the edge contrast to symbol contrast. A good Modulation means the printing process is taking full advantage of the contrast available. Good Modulation becomes important particularly as other areas degrade allowing for relative margin in the reading process. Modulation is calculated and graded for each scan and provided for the overall grade calculation in accordance with the ISO 15416 specification.The parameter grade and value provided for output is an average value for each measured scan over the entire symbol.
Defects
Defects are measurements of anomalies in the printed bars or spaces. These can be from be printing problem or from a variety of other sources such as scratches or problems with the substrate material. Defects, if large enough, can introduce spaces or bars that don’t exist, causing a misread or failure. Defects are calculated and graded for each scan and provided for the overall grade calculation in accordance with the ISO 15416 specification. The parameter grade and value provided for output is an average value for each measured scan over the entire symbol.
Decodability
Decodability measures the difference in dimension of the decoded symbol characters to the ideal. The further the characters are from the ideal, the more likely they are to fail to read or produce a misread. This can be caused by a variety of factors but can often indicate that equipment is not capable of printing at the resolution required or that the source data for the symbol has been improperly formed or degraded through transformation. Decodability is calculated and graded for each scan and provided for the overall grade calculation in accordance with the ISO 15416 specification. The parameter grade and value provided for output is an average value for each measured scan over the entire symbol.
Quiet Zone
Quiet Zone is an evaluation of the scan line before and after the start and stop characters. Required Quiet Zones are dependent on the symbology and evaluated in accordance with symbol specifications. Note that Quiet Zone is not an individually processed parameter within the ISO 15416 specification but is evaluated as part of the ISO graded decode parameter. A failing Quiet Zone scan will result in a failed Decode scan, which then feeds into the overall grade. The Quiet Zone parameter is provided as an average scan result where a passing scan receives an A / 4.0 grade and a failing scan receives an F / 0.0. When the serial output for Quiet Zone is a letter grade, 95% of scans must pass. When the serial output is a numeric grade, the output shows the passing percentage.
Overview
This section outlines the grading implementation of ISO 15415 in the reader firmware.
Supported Symbologies
Minimum Resolution
ISO 15415 Grading Serial Output
Each grade metric can be individually enabled for serial output. These outputs can be in one of three different formats configured by the global quality output mode parameter. The mode can be configured as a letter grade A-F, the actual measured metric values (0 – 100), or as a normalized grade value score where the grade A-F is mapped from 0-100. The enabled outputs are appended to the symbol data with the grading separator. They are appended in their order of appearance in the grade metric section.
ISO 15415 Grading Logic Output and Threshold 1 - 3
Each of the three logic outputs available can be configured and driven by each of the individual grade metrics. Each output has a corresponding configuration to enable and threshold each metric to control assertion of the output.
Aperture
The size of the aperture to use for grading is configured as a percentage of the nominal dimension of the symbol under evaluation. ISO 15415 is typically applied using an 80% aperture, but for controlled applications a smaller aperture may be more effective for process control.
Overall Grade
The Overall Grade is the lowest individual parameter grade. The is in accordance with the ISO 15415 specification.
Symbol Contrast
The Symbol Contrast is the difference between the highest and lowest reflectance values over the symbol region as measured by the aperture. Symbol Contrast measurements assume 8-bit 0 – 255 image intensity correlate to 0 – 100% reflectance. Symbol Contrast is calculated in accordance with the ISO 15415 specification.
Modulation
Modulation is a measure of how distinguishable dark cells are from light cells as it applies to properly decoding the codewords within the symbol. Modulation is calculated in accordance with the ISO 15415 specification.
Reflectance Margin
Reflectance Margin is a calculation that follows the procedure of Modulation but also takes into account individual cell state errors. Reflectance Margin is calculated in accordance with the ISO 15415 specification.
Fixed Pattern Damage
Fixed Pattern Damage is an evaluation of the elements in the fixed patterns of the symbol that are used for locating and extracting the data successfully. Fixed Pattern Damage is calculated in accordance with the ISO 15415 specification.
Axial Non-Uniformity
Axial Non-Uniformity measures the relationship between the overall dimensions of the two axes of the symbol. Axial Non-Uniformity is calculated in accordance with the ISO 15415 specification.
Grid Non-Uniformity
Grid Non-Uniformity measures the difference of the decoding grid in relation to the ideal grid formed from the four corners of the symbol. Grid Non-Uniformity is calculated in accordance with the ISO 15415 specification.
Unused Error Correction
Unused Error Correction measures the remaining error correction available after correcting the errors within the decoded symbol and is calculated in accordance with the ISO 15415 specification.
Overview
This section outlines the grading implementation for ISO 29158 in the reader firmware.
Supported Symbologies
Minimum Resolution
ISO 29158 Grading Serial Output
Each grade metric can be individually enabled for serial output. These outputs can be in one of three different formats configured by the global quality output mode parameter. The mode can be configured as a letter grade A-F, the actual measured metric values (0 – 100), or as a normalized grade value score where the grade A-F is mapped from 0-100. The enabled outputs are appended to the symbol data with the grading separator. They are appended in their order of appearance in the grade metric section.
ISO 29158 Grading Logic Output and Threshold 1 - 3
Each of the three logic outputs available can be configured and driven by each of the individual grade metrics. Each output has a corresponding configuration to enable and threshold each metric to control assertion of the output.
Overall Grade
The Overall Grade is the minimum grade of all evaluated parameters, noting minimum reflectance is not evaluated.
Cell Contrast
Cell Contrast is a measure of contrast that differs from ISO 15415 using a statistical value calculated from the measurements at the grid centers. Cell Contrast is calculated in accordance with the ISO 29158 specification.
Cell Modulation
Like Cell Contrast, Cell Modulation is a modified version from ISO 15415. Cell Modulation is calculated in accordance with the ISO 29158 specification. Note that the difference in the calculation for Cell Modulation versus the Modulation parameter in ISO 15415 also eliminated the need for ISO 29158 to adopt Reflectance Margin, which was added to the ISO 15415 specification.
Fixed Pattern Damage
Fixed Pattern Damage is an evaluation of the elements in the fixed patterns of the symbol that are used for locating and extracting the data successfully. Fixed Pattern Damage is calculated in accordance with the ISO 29158 specification.
Axial Non-Uniformity
Axial Non-Uniformity measures the relationship between the overall dimensions of the two axes of the symbol. Axial Non-Uniformity is calculated in accordance with the ISO 29158 specification.
Grid Non-Uniformity
Grid Non-Uniformity measures the difference of the decoding grid in relation to the ideal grid formed from the four corners of the symbol. Grid Non-Uniformity is calculated in accordance with the ISO 29158 specification.
Unused Error Correction
Unused Error Correction measures the remaining error correction available after correcting the errors within the decoded symbol and is calculated in accordance with the ISO 29158 specification.