First, even the best inks are not perfect, so the combination of cyan, magenta and yellow inks instead of a black almost always give a dirty-brown color, and secondly, the application too much paint on a certain stretch of paper leads to a glut of it, causing a noticeable reduction in print quality. To reproduce fine detail and deep shadows printers in addition to blue, magenta and yellow process inks using a fourth ink – black (CMYK). Separations to reproduce halftone color image through the printing machine, it (more precisely, it contains a page) must be subjected to color separation, and then display a single photo forms for each triad colors (cyan, magenta, yellow and black), and for each spot color used in the color design of this page. In Printing from the resulting photoforms made printing plates, which are installed in the press. (Printed forms for spot color is often called dies.) Technology UCR and GCR introduction of black paint in the color process Reproduction solved the problem of creating a black color that it was impossible to get a simple combination of 100 percent process inks CMY.
However, in some situations, this method causes other problems, such as excess paint on certain parts of the paper. In such cases, the printers use technology UCR (under color removal – subtract color from the color black) and GCR (gray component replacement – replacing the gray component) that allow minimize the total amount of applied paint on paper. UCR technology is primarily used to give depth to the shades of neutral colors and images.