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# What is Symbol Diagnostics (feature key required)?

Symbol diagnostics is a feature that provides graphical feedback from the device for NoRead barcodes. By looking at the feedback, you can troubleshoot why a barcode failed to decode. The feedback provided can signal the following issues (in a region of the barcode):

- Start or Stop pattern was not found (orange arrow on code). The region designated by the arrow failed to decode. Reasons for failure are as follows (please check the corresponding Tech Note for detailed images that illustrate each case):

  - The Start or Stop pattern is clipped/damaged

  - The code is clipped (due to image boundary or by an object blocking the code)

  - Image quality degradation (often, but not always, caused by light quality)

  - Warping and folding of barcode labels

- Damage/print-error inside the barcode (red rectangle region on code). The region within the rectangle is where the damage or printing issue is found. Common examples of printing issues are (please check the corresponding Tech Note for detailed images that illustrate each case):

  - Leaking ink that merges bars into one

  - Misprint of a bar that reduces its thickness beyond decoding tolerance

- Quiet Zone is not sufficient (magenta rectangle region on code). Quiet Zone violation occurs when there is not enough space on one or both sides of the barcode. Depending on the symbology, readers tolerate some Quiet Zone violation. Quiet zone violation usually happens due to text or rectangle around the barcode being too close to the barcode on one or both sides or because the code was clipped by the image boundary (please check the corresponding Tech Note for detailed images that illustrate each case).

- Checksum verification failed (blue rectangle around the code). Common causes for Checksum validation failure are as follows (please check the corresponding Tech Note for detailed images that illustrate each case):

  - Damaged barcode (barcodes can be folded and aligned such that all the data characters decode, but it is a NoRead still, as checksum verification is not passed)

  - Incorrect pattern is printed (the encoded string and the printed barcode pattern don’t match and if the symbology supports Checksum, then the decoder can indicate such failure)

In addition to graphical diagnostics, Symbol Diagnostics returns readability metrics for each NoRead result, shown at the top left corner of NoRead codes. Metrics can help you assess the image or print quality and help in improving the existing setup.

Symbol diagnostics is only available for uploaded PNG images (Actions>Images>Upload Image) that are signed by a Cognex reader (not necessarily the same reader; images are signed automatically when saved from any reader). After uploading an image, check the Image Panel or Quick Setup image window for Symbol Diagnostics feedback.

In addition to graphical diagnostics, Symbol Diagnostics returns readability metrics for each NoRead result. Metrics like Symbol Contrast and Minimum Edge Contrast can help users assess the image or print quality and help in improving the existing setup. The metrics are shown at the top left corner of each NoRead barcode.

The table below shows a mapping between the displayed metric name and its full name. Please refer to the Readability Metrics to understand what each metric measures.

Full Name Displayed Name Possible Grades Symbol Contrast C A,B,C,D,F Minimum Edge Contrast EC A,F Print Growth PG A,F Minimum Reflectance MR A,F

Note: Note: Symbol Diagnostics is a feature that is activated exclusively by feature key.

Note: DM070,DM150,DM260,DM300,DM360, DM370,DM280, DM470, DM503