Measuring CMYK Halftones: The Case for Spot Color Tone Value Formula

The adoption of Spot Color Tone Value (SCTV) in ISO 20654:2017 represents a clear improvement over the density-based Murray-Davies TVI model for the characterization of spot color halftone gain, providing a closer correspondence with dot area and visual impression. However, CMYK halftone gain is still commonly characterized by the TVI method, and the continuation of this practice presents several challenges to practical process control of print jobs containing both CMYK and spot colors. The adoption of Colorimetric Tone Value as the default model for characterizing halftone gain of both spot colors and CMYK is proposed. Advantages include reduction of ambiguities in software and instrument displays and usability with a wider variety of CMY colorants. Disadvantages to be overcome include user unfamiliarity with the newer methods and metrics and certain incompatibilities with existing colorimetric target aims. Practical recommendations are made for providing backward compatibility of CTV with legacyprint specifcations by means of simple compensation curves.