The CMY color model works with the primary colors of subtractive color mixing and is used for reflective media, i.e. for printing equipment. The color space of the CMY color model is smaller than that of the RGB color model; this means that fewer colors can be reproduced with this model.
From these primary colors CMY, the secondary colors red, green and blue can be formed, as well as the achromatic colors black and white. If, for example, the primary colors magenta and yellow are combined, the result is the secondary color red, i.e. a primary color of additive color mixing. The brightness axis runs on the diagonal between black and white.
When printing with the three primary colors cyan, magenta and yellow, the color black cannot be printed in sufficient depth, which is due to the inks used in practice, the CMY model has been extended to include black to form the CMYK color model. Where "K" stands for depth and contrast and is printed in black. There is a direct connection between the three color models CMY, CMYK and RGB, which can be established via the UCR process, Under Color Removal (UCR), or the GCR process, Gray Component Replacement (GCR).