RGB and CMYK are the two most common colour models in graphic design. RGB stands for red, green, and blue, the primary colours for digital displays, such as computer monitors, TVs, and smartphones. CMYK stands for cyan, magenta, yellow, and black, the primary colours used for printing. The main difference between RGB and CMYK is the way colours are mixed.
RGB – MIXING LIGHT
RGB uses an additive colour model, meaning that colours are created by adding light. For example, when you combine red, green, and blue light, you get white light. RGB also offers a superior colour range (gamut). Each RGB colour has values ranging from 0 to 255. In short, this translates into 16,777,216 possible colours.
CMYK – MIXING PAINT
CMYK uses a subtractive colour model, meaning that colours are created with light subtracted. For example, when you mix cyan, magenta, and yellow paint together, you get black paint. The CMYK colour gamut is smaller than RGB, which is why, when colours convert from RGB to CMYK, you see many colour differences occur.
Why is black 'K' in CMYK and not CYMB?
Black is referred to as 'K' for Key, Key Colour, or Key Plate – a vital colour with full-colour printing, but also 'B' is too ambiguous as it could stand for blue (as found in RGB), brown or beige.
Colours misbehaving?
In today's artwork world, using the colour mode of the output intent is always good practice. However, if you produce artwork for both screen and print, which method is better and why?
If artwork is to be printed, RGB colours must be converted to CMYK at some point in the process. If left to computer software to convert colours, whether when PDF files are exported or relying on the printer's prepress system to convert, managing colours within your artwork would be outside your control. Also, the printer will not see how you see colours on your screen. As a result, you will likely encounter vibrant colours that will dull; oranges appear brown, bright greens darken, or there is a shift in colour, such as royal blues printing with a greater hint of purple. In short, results can be disappointing.
We would never solely rely on any pre-press process to blindly convert RGB colours. Instead, we prepare images and artwork as the print output device requires, minimising any colour changes that could occur later in the process; we are in control.
Every image a client provides receives colour treatment, profile management, balancing, and enhancement to ensure images replicate as we intend. We do most of the work in RGB before converting to CMYK and making further adjustments if required before saving and ready for placement.
Compare this to other providers who aim to save time, simply drag-and-drop unmanaged RGB images, resulting in poor colour and/or dark (over-saturated) images. Here's a typical example of what we frequently hear.
What do designers prefer?
Designers offer valid opinions as to why working with RGB is better; others CMYK, and those that advocate the latter are likely to have gained more insightful experience working with commercial printers — as we have, showing greater consideration with the technicalities of colour and how it can behave on specific substrates (materials used to print on). We consider possible outcomes when constructing artwork regardless of whether it appears on screen or in print.
How to maintain better RGB / CMYK colour consistency
A simple trick to help gain better control and consistency with colour is to convert RGB images to the smaller CMYK colour gamut, make colour adjustments, and then change the colour mode back to RGB again. Because colours in the wider RGB colour gamut now sit within the CMYK gamut, what you see on screen is more likely to give you more confidence in how the colour will look when printed.
An often-overlooked problem
With black text you read on screen, RGB colour values are all set to zero – nothing. Converting nothing from RGB to CMYK achieves the opposite, adding a lot of colour to each channel to achieve a similar black. As RGB, black is 0% Red, 0% Blue, 0% Green, but as CMYK, it's likely to be 91% Cyan, 79% Magenta, 62% Yellow and 97% Black. These heavy colour values pose a significant problem with paragraphs of black copy, for example.
As colour values are now applied to all four C, M, Y and K channels, it greatly increases the chances that fine text will look blurry if any of the four CMYK colours do not precisely register (ink overlaying on top of one another). It's a typical printer's nightmare.
The only way to achieve precise definition with black text is to apply the text to the 'K' key colour, which means additional production work is required to correct or, better still, work with CMYK from the outset, keeping bodies of text to the black-only 'K' channel.
CMYK for digital publications?
Yes, well, only as long the artwork is being constructed simply because we can easily convert CMYK-based artwork to RGB, ensuring better consistency with colour without incurring any technical issues. It also means all pages are print-ready for any digital-print or litho-print CMYK process if ever the client requires, at any time in the future, swiftly supplying colour-accurate artwork for print in minutes without the need to rework or revisit assets.
If you're looking for a short answer, CMYK covers all possible output processes while ensuring colour consistency is maintained.
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