What is Edge Contrast?
This is a measure of local contrast between two adjacent elements. It is defined as the difference of the highest and lowest reflectance values (Rs and Rb respectively) in a pair of adjacent elements (bar + space or space + bar). Quiet zones are considered spaces for this purpose. Every element has its own value of Rs or Rb. The lowest Edge Contrast (ECmin) in a profile determines the grade for the parameter; this is also a pass/fail graded parameter (grades 4 or 0 only) where, if ECmin is less than 15%, it is graded 0. Variations in ink weight in different parts of a symbol, or fluctuations in the background reflectance (e.g. with corrugated brown kraft substrates) are one cause of Edge Contrast problems, but another is that scanners tend to see narrow elements less distinctly than they do wider ones (a narrow space has lower apparent reflectance than a wide one, and a narrow bar appears similarly lighter than a wide one).
