The effects on hue resulting from black overprinting in halftone reproductions

A type of black printer that only existed in theory is now being applied in the printing industry. The process which makes use of this black printer is known as gray-component replacement. Developed from the extension of the undercolor removal process, the use of gray-component replacement in printing halftone reproductions is said to result in numerous technical and cost benefits. When used to the maximum, the process eliminates one of the three process color inks in a given unit area and prints black ink from highlight to shadow. A problem can result from the use of this process as it applies a greater amount of an opaque black ink in combination with selectively transparent colored inks. Where this black ink overprints one or more of the three colored inks there will be an increase in unwanted absorption and a decrease in the wanted absorption. The result of such overprinting will be the alteration of the reflectance curve of the reproduction as compared to the original with the result being a shift in hue. An experiment was performed to demonstrate the principles. Several tint patches were printed with the only difference between each patch being the location of black ink overprinting within the tint. It could be seen by visual analysis that a hue shift did occur. Sample tint patches were analyzed by means of a spectrophotometer to objectively describe the visual results