T
o use colour effectively, it must be kept under tight control. The
colour workflow begins with the designer’s ideas and the customer’s
specifications. From there, these colours must be communicated among
several different individuals who will render and reproduce the colours
on many different devices. At each stage of production, output from the previous
step becomes the input for the next process. Every exchange brings the colour
into a new colour space – from a photographic scene, to monitor RGB, to CMYK
process proofing, and printing on a variety of systems. And every evaluation is
made by a different viewer under new viewing conditions.
So, how do we ensure that our original ideas and specifications will remain
intact throughout this complicated process? This article is designed to answer
that very question. In short, the answer is colour measurement – if you can
measure colour, you can control it. The remainder of this booklet explains the
fundamentals of colour communication, measurement, and control.
The Challenge: Colour Communication
Consider the many different individuals who 'pass the baton' of responsibility for
keeping the customer’s colour specifications intact:
•
Client
Defines message; determines image concept; provides general or
specific colour and paper specifications.
•
Graphic Designer/Photographer
Provides image, art, and page files;
and printed or digital colour specifications.
•
Prepress Service Provider
Provides final colour-separated materials; colour
break information; printed or digital colour specifications.
•
Materials Supplier
Provides inks and paper that meet colour specifications.
•
Output Service Provider
Provides final prints; meets colour specifications.
Each step in the colour reproduction process adds value and content to the
message. Good colour specification ensures that each process provides accurate
colour content based on the input received.
As we strive to create dazzling, high-quality colour documents and designs,
we struggle to control colour at each production phase. Each viewing situation
presents its own interpretation of the same colour. For example:
• Our original scene contains a wide range of natural, vivid colours.
• A photograph of the scene captures much of the scenes colour; however, some
of the dazzling tones are lost when the image is scanned into RGB data. Still
more colours are lost or changed when the scan is displayed on a monitor –
and the scene appears slightly different on different monitors.
• As we move our artwork between imaging, illustration, and layout programs,
the colours are specified in different ways. For example, specifying 87 percent
magenta / 91 percent yellow produces a slightly different colour in Adobe
Photoshop, Macromedia FreeHand, and QuarkXPress.
• When we print our artwork, the colours are colour-separated from RGB data
into CMYK data. The colours are interpreted a bit differently on different
devices – on our laser copier, our prepress providers proofing system, and
on press.
• When we check our output, we view the colours under different lighting
conditions that affect colour appearance in different ways. Also, different
individuals perceive colours based on their own vision skills and memory.
The common question throughout this process is: which device is telling the
truth? Unfortunately, no individual viewers, programs, or devices can reveal the
true identity of a colour. They simply perceive the colour’s appearance, which can
be affected by lighting and other factors.
The Solution: Colour Measurement and Control
Measurement is the key to total production control. Consider this: we measure
size in millimetres; weight in grams; and so on. These scales allow us to establish
precise measurement standards that can be repeated in the production process.
This ensures that all manufactured items are identical and within our quality
tolerances. Using measured colour data, we can do the same for colour – we can
monitor colour at each stage of production and check the 'closeness' of colour
matches using repeatable, standardised numerical data. So, what properties of
colours allow them to be discretely identified and measured?
Let’s find out by examining these properties – how colour happens in nature and
in our minds; how it is reproduced on screen and on paper; and how colour can
be communicated as reflectance values (spectral data) and as three-dimensional
values (tristimulus data).
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