In four colour process printing, which is also known as CMYK, which are the only four colours that are used?
Spectral printing Spectral printing Spectral printing is the art and science of reproducing the spectra of a scene-referred image, by means of hard-copy printing using more than four process-colour printing inks namely cyan, magenta, yellow and black and their lighter versions. The additional secondary inks are often referred to as spot colours. As opposed to normal four-colour process printing, the aim of spectral printing is to eliminate or reduce metamerism either due to illuminant or observer. A side effect of printing with more than four primary inks is that it enables an improvement in colour gamut of the printed image due to
CMYK color model and ink in use. Processes called under color removal, under color addition, and gray component replacement are used to decide on the final mix; different CMYK recipes will be used depending on the printing task. CMYK or process color printing is contrasted with spot color printing, in which specific colored inks are used to generate the colors appearing on paper. Some printing presses are capable of printing with both four-color process inks and additional spot color inks at the same time. High-quality printed materials, such as marketing brochures and books, often include photographs requiring process-color printing, other graphic effects requiring