The Postal Service requires a print reflectance difference (PRD) of at least 30 percent in the red and green portions of the optical spectrum between the background material of the mailpiece and the barcode, when measured with a USPS or USPS-licensed envelope reflectance meter. (PRD equals the reflectance of the background minus the reflectance of the ink.) Black ink on a white background usually satisfies this requirement, and the Postal Service recommends it.
FIM bars must be printed within the dimensions shown in Exhibit 10-2. The bars must be within 5 degrees of perpendicular to the top edge of the mailpiece.
