A little bit of theory...

The spectrum of the colours distinguished by the human eye is enormous. Unfortunately, the range of the colours displayed on a screen or in print is significantly smaller. What is more, the range achievable in print does not correspond exactly to the range of colours on a screen. Even though the ranges of CMYK and RGB do overlap partially, they differ significantly in the way the human eye perceives the colours.

The colours displayed on the screen (the additive colour model) look completely different in print (the subtractive colour model). The image emitted by an RGB screen utilises the emission of radiation and enters directly to the eye of the recipient. A 100% combination of red, green and blue is perceived as white, whereas a 0% combination gives the impression of a black colour. In the subtractive model, the pigments used in the print will absorb certain colours from the light reflected from the print thereby giving a sensation of a certain colour. For example, a pigment absorbing blue will give an impression of yellow (the eye receives the reflected red and green). Of course, depending on the type of paper, the colours will be absorbed in a varying degree - that's why the type of surface used is such an important element when determining colours.
Due to the quality and amount of paint needed to obtain a black colour in print, it seemed necessary to use an extra colour.
The subtractive colour model with an extra black colour (CMYK) is a standard in full-colour offset printing.

The image seen on a screen consists of pixels. Full colour offset printing is created by printing overlaping raster dots in CMYK colours.


The ready-made draft, before it goes to print is broken down into colour extracts describing the colours in four-colour print: cyan, magenta, yellow, black. Raster dots printed on each other at a specific angle form the image.

The formula guide not only makes the printers job easier, but, more importantly, allows to achieve the exact effect desired by the customer. Depending on the type of work, different products should be used.

For example, determining a colour needed for painting a wall in CMYK or PANTONE would not make any sense. NCS or RAL would be used in this case. The same principle applies for the reverse situation - determining a colour with the use of NCS or RAL in offset printing. It would be necessary to use CMYK or PANTONE. Of course when using different formula guides it is possible to compare the colours from different systems. However, this way of colour selection will not be unequivocal and the colour obtained will only be an approximation.