Grey Component Replacement

The gray component replacement is a possibility of image construction in multi-color printing.

Four color printing with gray component replacement (GCR)

From the theory of colors by Harald Kueppers results for the four-color printing, the alternative possibility of the Gray Component Replacement (English: Grey Component Replacement, GCR ). Now all achromatic arise in the printed image by subsets of the black ink, which interact with the rest of the unprinted areas of white printing paper and so produce the achromatic values . Subsets of the chromatic printing inks YMC are now only needed to form the chromatic values of the colors. In principle, by the technology of four-color printing has been turned upside down. Because now you are working with skeleton -tone color separations for the colorful inks CMY and with a full color separation for black.

This technology of course, assumes that the ink black actually looks black, so bring a neutral density of at least 3.0. Where this is not the case, the lack of neutral density of black can be supported by respective subsets of the colored printing colors CMY. But this happens only in the neutral image depths. This is called UCA ( Under Color Addition).

If you want to paint a picture, there are two extreme possibilities. The painter may be different for each image point on his palette mix the desired color and then apply the image. But it can also first paint a black and white image, which he then colored. So the colored copper engravings were made earlier. The first described method corresponds to the chromatic composition, the second corresponds to the gray component replacement. The achromatic brings advantages: Significant stabilization of the printing process; lower ink consumption; less drying problems; less waste; improved image reproduction.

Seven-color printing with achromatic

The inks of the four-color printing do not possess the ideal properties that they should have. You have spectral errors, called false false reflections and absorptions. The inks One can not construct as they would like to have. You have to work with the solutions that are given in the color chemistry. For this reason it is impossible to reproduce pure bright color nuances in the secondary RGB colors in four-color printing.

This deficiency is addressed by the seven-color printing. In addition to the chromatic printing inks CMY print RGB colors are thereby added. In theory the seven-color printing only with achromatic. Process safety is further improved upon considerably; the ink consumption is again reduced; also falls again to less waste; Problems of drying omitted. And the quality of the image reproduction is improved tremendously. Because in the critical areas of secondary RGB whiter, brighter colors are reproduced. This of course has its price. It must be seven color separations produced and seven plates are copied. And the printed sheet must pass through seven color works. But for large print runs, these increased costs are more than offset by the resulting savings.