What is Symbol Contrast?
The Symbol Contrast is the difference between the highest and the lowest reflectance values in the profile. The maximum reflectance (Rmax) may occur anywhere, in a space or a quiet zone. The minimum value (Rmin) will always be in a bar. The importance of this parameter is that the higher the Symbol Contrast, the more easily distinguishable from each other the bars and spaces will be. SC of 70% or higher is graded 4, while SC below 20% is grade 0. ——— Minimum reflectance (Rmin) Rmin must always be no higher than half of Rmax. This is because, for a given level of Symbol Contrast, many scanners have greater difficulty distinguishing relatively light bars against a high-reflectance background than they do darker bars against a relatively low reflectance background. This will tend only to affect symbols with grade 2 or 1 Symbol Contrast, where the value of Rmax is in the upper part of its range. It is a pass/fail parameter: it is assigned grades 4 or 0. The symbol shown in Figure 4 below,
