CMYKrum

CMYKrum is a proposed color encoding framework used in discussions of printed color reproduction. It extends the conventional CMYK color model by incorporating an additional chromatic- and substrate-aware component, referred to as the rum channel, to better capture how inks interact with different papers and coatings. In practice, CMYKrum seeks to describe both ink colorants and substrate effects within a single, device-oriented model, facilitating more consistent color prediction across printing devices and materials.

The model treats color as a five-dimensional vector (C, M, Y, K, R) where C, M, Y, and K are the four standard process inks expressed as percentages, and R (rum) encodes non-ink factors such as paper whiteness, surface texture, coating, and metameric shifts. R is derived from calibration measurements on target substrates and is intended to be as device-independent as possible. Conversion to perceptual spaces (such as CIELAB) involves a forward mapping that combines the CMYK components with the rum value to approximate the observed color.

Applications of CMYKrum are primarily in color science research and educational contexts, where the goal is to study how substrate variability affects color reproducibility and to illustrate limitations of traditional CMYK predictions. It is not a standardized color space or widely adopted in commercial workflows, due to lack of consensus on the rum parameter and added computational complexity.

The term CMYKrum originated in academic discussions in the early 2010s as a thought experiment for substrate-aware color modeling. While it has influenced analyses of metamers and ink-substrate interactions, it remains a conceptual framework rather than an industry standard.