Colour modes are a crucial yet often overlooked aspect of design (typically by those accustomed to designing for web). Using an incorrect colour mode can have a detrimental effect on the finished product, most notably the colour printed may not be the colour expected. It is important that you know when to use what colour mode and why. This article will explain why.
The colour you see on a computer monitor is not the colour you will see on the printed page. Different methods of printing are used for different requirements and quantities, and together with varying stock types, colour may appear quite different to that seen via the computer.
CMYK – the colour mode used for print design
The letters CMYK stand for cyan, magenta, yellow and black (or key). Theoretically, the addition of black is superfluous, since a uniform mixture of cyan, magenta and yellow produces black. In practice, however, mixing the former three usually results in a dirty brown-grey tone, which justifies using black as the fourth colour. These primary printing colours are responsible for mixing all the other colours required in a printing press. This is achieved by the printing numerous tiny dots in one of the respective colours so close together that the human eye perceives the group of dots to be a single dot with a specific colour.
The problem in the relationship between RGB and CMYK is that the RGB colour space contains colours the CMYK colour space cannot reproduce: In other words, things that looks great on the monitor may look different, and not quite as attractive in print.
To keep discrepancies to a minimum, powerful image editing programs offer the option of converting an RGB image into the CMYK mode – this is one of the meanings of the term colour space. Display images, such as for the Web, do not need to be in the CMYK mode. This mode becomes important when the images are to be printed on professional printing presses, or if you would like to simulate the expected results before starting a large print job (proofing).
RGB – the colour mode used for web design
A pixel displayed on screen actually consists of three tiny phosphor dots, each of which emits a specific shade of red, green or blue when hit by the electron beam of the picture tube. Together, these three dots determine the colour of the monitor pixel; when they all shine at full intensity, they produce white.
In principle, RGB is a colour mode that offers numerous radiant colours. However, the word “radiant” also indicates the drawback of this type of colours, because a computer monitor emits the colours as a primary light source, something a piece of paper with colours printed on it cannot imitate. On paper, we see colour when the ink pigments reflect the corresponding colour components of the light. Corresponding “reflectors”, which replace the “primary light sources” of the monitor, are usually produced by mixing the primary printing colours, which are abbreviated C, M, Y, and K.
A common problem when supplying files for print is submitting them with the RGB colour mode. This can cause issues in the printing process both digitally and offset.
It is strongly recommended that all files be created in CMYK mode, and all imported content converted to CMYK if in RBG.
When converting images to Grayscale, certain information describing the image content may be lost. Tonal adjustment is recommended to help alleviate this problem.
Do not use spot colors in your file unless you specifically require spot colours (which generally is more expensive). Otherwise, convert all spot colours to CMYK before submitting artwork.
While in theory, black ink should be as dark a color as you can print, in reality, black ink is somewhat translucent. An even darker color can be achieved by combining black with secondary color (typically 30% Cyan 30% Magenta 30% Yellow 100% black). This is called a “rich black” or as we like to call it "Isn't that a beautiful black!"