Page 111 - Graphic Design and Print Production Fundamentals

4.5 Working with a Spectrophotometer to Read Standard Colour

Charts for Output Profiling

Alan Martin

Armed with our fundamental concepts in colour theory, we can apply these principles to the physical
process of colour management. The practical application to print production requires a procedure for
measurement, colour profile generation, and the correct use of profiles in the manufacturing process.
Let’s begin with measurement and discuss the working components of a standard graphic arts
spectrophotometer and the colour charts we would use it with.

X-Rite i-One (i1) Pro Spectrophotometer

The i1 Pro is one of the most common hand-held spectrophotometers used in the graphic reproduction
industry. It can also be mounted in the iO base for automated scanning. As described in section 4.3, the
spectro works by recording spectral data from incremental slices of the range of wavelengths included
in visible light. To do this properly, the spectro must calibrate its white point to establish the baseline
for interpretation. It does this by reading the white tile supplied in the baseplate that comes with the
spectro. Each baseplate is uniquely matched to a specific spectrophotometer and marked with a serial
number that corresponds to its spectro. Make sure you confirm that you have the correct baseplate that
matches the serial number on your spectro. When used commercially, the manufacturer recommends that
a spectro be returned for factory recalibration every two years. The packaging will include a certificate
indicating the expiry date for the current calibration.

The spectro may also be identified (on both the serial number tag and surrounding the light-emitting
aperture) as a UV-cut. This indicates it has an ultraviolet filter, which acts to remove the impact of
fluorescence from optical paper brighteners. If you have access to more than one spectro device, be sure
that any related measurements are done consistently either with or without the filter. Best practice is to
use exactly the same instrument for any series of measurements.

The USB cable provides power to the spectro and so should be plugged directly into the computer
and not into a peripheral such as a keyboard. Additional typical accessories for the spectro include a
weighted strap and screw-in base for hanging the spectro against the screen of a monitor and a proof
mount base with sliding rail for the spectro to read printed colour targets.

Colour Charts or Targets

You will typically be dependent on the colour management software application that you have chosen
to produce a pdf file of the colour chart that your spectro can read. While in the software, you select a
reading device (such as the X-Rite i1 Pro or i1 iO) from the list of devices that the software supports
and then provide the dimensions for your output device. The choice of reading device will determine the

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