Color printing

Traditional color printing had the following drawbacks:

1. It is quite difficult to keep the colors balanced, as the printing process is exposed to varying ambient conditions, such as room temperature, humidity, paper quality. Hence the danger that the composition varies and that one of the color components is enhanced, changing the appearance of the whole resulting color.
2. The ratio of total color applied is very high. This refers to the sum of the percentages of the different color components: e.g. a gray that consists of 80% Cyan, Magenta and Yellow has a total color application of 240%. As different types and qualities of paper heve different capacity to absorb color (trapping), one must heed the total color application, as this also influences the drying time and in a worst case can cause the color to leak through the paper.

Moreover, we must consider that color is the most expensive material component of the printing process. Alternatives have been developed mainly out of the necessity to reduce total printing costs.

Alternatives developed to reduce these drawbacks are:

1. Under Colour Removal (UCR). In this process a part of the gray component is being substituted by black. In the variant of Under Colour Addition (UCA) the same results can be obtained, but from a different starting position.
2. Grey Component Replacement (GCR). Contrary to UCR not just gray, but also coloured components are being substituted by black. An example:

In four-color printing, the Under Color Removal (also short UCR) is a technique to convert from the CMY color space into the CMYK color space. Grey areas composed of all three colors—cyan, magenta and yellow—are converted into only the fourth black channel.

Related techniques are the Under Color Addition (UCA), in which small portions of the three colors are added to the uncolored areas. The Grey Component Replacement does not only add black to uncolored areas, but also to slightly colored ones, as black color is much cheaper than colored one.