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.
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.
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.