The Deviation Between Visual and Instrumental Chroma for Printed Color Inks.

The addition of low concentrations of a neutral black ink to colored inks resulted in an increase in chroma for selected prints having different film thicknesses. Visually, the prints were judged to be lower in chroma. When chroma was measured for sample pairs having nominally the same film thickness, two of nine hues showed an increase in instrumental chroma when black was added. The increase in chroma was greatest with 0/45 and 45/0 spectrophotometer geometries, and less with sphere geometry. Unexpected chroma reversals occurred between sample pairs of the same hue made with coated and uncoated stock. The agreement between visual and instrumental chroma was poorest with 0/45 geometry followed by 45/0 and sphere geometry. The overall visual agreement was significantly better for uncoated stock.