Saturday, 16 February 2013

RGB v CMYK - Do You Know Your Colours?



At Media Design and Print, one of the most common queries we regularly receive relates to colour reproduction.

Below is a fairly in-depth explanation on the problems that can sometimes be encountered with specific shades and hues, but we hope it helps you understand the processes involved when our expert team produce your projects just how you want them.

 
CMYK or RGB Color?
Most graphics software programs give you the choice to work in either RGB or CMYK color. These are also called colour spaces. There are colour spaces other than RGB and CMYK but they are less common and we will not discuss them here.

What is RGB Color?
Digital cameras and scanners and create images using combinations of just three colours: Red, Green and Blue (RGB). These are the primary colours of visible light and this how computers and televisions display images on their screens. RGB colours often appear brighter and more vivid specifically because the light is being projected directly into the eyes of the viewer.

This is an "additive" process in which the three colours are combined in different amounts to produce various colours. It is called "additive" because you must add varying amounts of two or more colours to achieve hues and values other than the three basic red, green and blue colours.

Computer monitors and televisions vary the amount of each colour from 0 to a maximum of 255. Equal maximum amounts of all three colours (often expressed as R255, G255, B255) creates white. The absence of all three colours (R0, G0, B0) creates black. Equal amounts of all three colours somewhere between 0 and 255 will create varying shades of gray.
 

RGB (additive) Colour
Many graphics applications default to the RGB colour space because computers use RGB to display colour themselves. It is easier. Most software and even desktop inkjet and laser printers assume that you are using RGB colour to simplify things for users. However, strange as it may seem, all desktop inkjet printers actually use CMYK (or at least CMY) to produce colour documents. Not all printers use the black cartridge when printing colour, the cheapest models may use equal amounts of Cyan, Magenta, and Yellow to produce Black (often poorly).

What is CMYK or Process Colour?
Based upon Sir Isaac Newton's Colour Circle, Four colour process printing was originally developed in the late nineteenth century along with the halftone process for reproduction of continuous tone images (photographs) and has been used for over 100 years to reproduce colour images. The colours Cyan, Magenta, and Yellow appear directly opposite the Red, Green, and Blue on the Colour Circle devised by Newton over 300 years ago.

Newton's Colour Circle
Professional printing presses print full colour pictures by using the colours Cyan, Magenta, Yellow and Black (CMYK). In this "subtractive" process the various inks absorb the light reflected from the underlying white paper to produce the colours that your eye sees. The colours that you see are those colours which were not absorbed by the ink. It is called subtractive because when you subtract the other colours, the colour that is left is the colour that you see.

In the CMYK colour system, equal proportions of Yellow ink plus Cyan ink produces Green, Yellow ink plus Magenta ink produces Red, and Cyan ink plus Magenta ink produces Blue (actually more like purple to most eyes). Various colour shades and values are achieved by varying the relative amounts of the four coloors. Black ink is added to improve the quality of 3-color blacks, to provide added detail to images, to speed drying, and to reduce overall ink costs, thus the name: Four Colour Process.


CMYK (Subtractive) Colour
This is the Four Colour Process (also known as Process Colour or Full-Colour) printing that comprises the vast majority of magazines and marketing materials you see every day. Process colour is generally very good for reproducing pictures but there are some types of colour that it cannot reproduce well. This is because the gamut (or range) of reproducible colour for Process Colour is not as wide as that of RGB colour. As a result, certain intense values of colours such as Orange, Green, Blue, and other bright colours can sometimes appear dull or even dirty. On the other hand, bright Reds generally reproduce very well.

That is not to say that CMYK colour looks dull or dirty. Just look at any colour magazine such as The National Geographic and you will see that it does a very god job of reproducing nearly every colour that might be needed. For those special colours that cannot be satisfactorily reproduced by CMYK there is always spot colour (special extra inks that are mixed to match a specific colour or even a customized colour). Spot colours are often used for metallic and other special effects colours.

It is best to select any colours you use for fonts or other design elements in your layout using CMYK definitions instead of RGB. That way, you will have a better idea of how they will appear in your printed piece.

RGB Must be Converted to CMYK Colour in Order to Print
At some stage your RGB file must be translated to CMYK in order to print it on a printing press. It is best if you do the RGB to CMYK Conversion of your images. You will have more control over the appearance of your printed piece if you convert all of the images from RGB to CMYK before sending them to us. Be aware that it is possible to create colours in RGB that you cannot reproduce with CMYK. These are beyond the CMYK colour range or "out of the CMYK colour gamut".

Here are some examples of how various RGB colours convert to CMYK:

RGB Colors (what you see on screen)


CMYK Colours (printing inks will do this)

You most likely won't notice this kind of colour shift in a colour photograph. It is more likely to happen if you pick a very rich, vibrant colour for a background or some other element of your layout. It probably won't look bad, it just won't look exactly the same. But it may not be noticeable at all either.

You can purchase a colour guide with thousands of process colours with their RGB values and their CMYK screen percentages, to help you choose the right colour for your project. We recommend the PANTONE Color Bridge Set which contains both coated and uncoated stock ink swatches.

When we receive RGB images in a job we instruct our RIP software to make the conversion to CMYK. The RGB to CMYK conversion table tries to map colours to get as close as possible to the appearance of the original. We think that it does a very good job but it is possible that it might not be to your liking.

Here is an example: many programs translate the 100% Blue in RGB into a purplish blue colour in CMYK (Adobe InDesign will give you C:88, M:76, Y:0, K:0). We suggest that you use a CMYK value of C:100, M:60, Y:0, K:0 to get a nice blue. Working in the CMYK colour space allows you to select the exact CMYK mix that gives you the results you want.

We want you to be pleased with your job, so please, take the time to prepare your file properly. We cannot be responsible for results if you furnish your images in RGB. Even though monitors always use RGB to display colours, the colours you see on your monitor will more closely match the final printed piece if you are viewing them in the CMYK colour space.

So there you have it. Whether it's a simple A5 leaflet or an A1 photo print there's more going on in the background after you've sent us your PDF than you may at first think.

In all instances, if you are unsure about your project, please feel free to call us on 028 9045 9864 or email printing@mediadesignandprint.com and the team at Media Design and Print will always be pleased to advise.

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