What are Defects?
Spots of ink in the quiet zones or spaces, or light areas in the bars, will cause a ripple in the scan reflectance profile at the point where the scan path crosses them. This is referred to in the profile analysis as Element Reflectance Non-uniformity (ERN). In the profile of a space, they show as a valley; in that of a bar, they show as a peak. If this peak or valley approaches the threshold between light and dark, the risk of the element being seen as more than one, and of the scan failing to decode, increases. As already indicated, the use of the correct measuring aperture ensures that the effect of defects is not exaggerated or underrated. The defect parameter measures the relationship of the depth of the highest peak or deepest valley to Symbol Contrast (Defects = ERNmax/SC), indicative of its relative severity.
