Colour Management

Glossary of terms

Profile Assignment: The action of tagging or embedding an image with an ICC profile so that the profile is part of the image and

stays with the image until its explicitly removed

Calibration: Changing the behaviour of a device to conform to a standard or norm. This is done as a precursor to profiling

Characterisation (Profiling): Also known as profiling/measuring the colour behaviour of a device

CIE: Commission Internationale d’Eclairage (international Commissions of Illumination) is an international body of colour scientist

who come up with many of the standards used in colour management

CMM: Colour Matching Module: The mathematical engine that does the conversion from one profile to another. Windows Colour

Management Module, MAC colour Sync, Adobe CMM

• Colour Model: A system for defining a colour as a series of Numeric values – For example RGB, CMYK or Lab

• Colour Space: The range colour achievable by an individual monitor, printer, scanner etc. This is often used interchangeable with gamut and

the term profile

• Colorimeter: A device used for measuring colours, usually a monitor

• Workflow: The process of capturing an image, through the raw conversion, post processing and output

• Spectrometer: A device for measuring spectral characteristics of light, used for profiling printers

• RGB: (Red, Green, Blue) describes what kind of light needs to be emitted to produce a given colour. Light is added together to create form

from darkness. RGB stores individual values for red, green and blue. RGB is not a colour space, it is a colour model. There are many different

RGB colour spaces derived from this colour model, some of which appear below.

RGBA is RGB with an additional channel, alpha, to indicate transparency.

• SRGB: The sRGB colour space, or standard RGB (Red Green Blue), is an RGB colour space created cooperatively by Hewlett-Packard and

Microsoft Corporation for use on the Internet

• CMYK: CMYK is used in the printing process, it describes what kind of inks need to be applied so the light reflected from

the substrate and through the inks produces a given colour

• ADOBE RGB(1988): The Adobe RGB colour space is an RGB colour space developed by Adobe Systems in 1998. It was designed to

encompass most of the colours achievable on CMYK colour printers, but by using RGB primary colours on a device such as the computer

display. The Adobe RGB colour space encompasses roughly 50% of the visible colours specified by the Lab colour space, improving upon the

gamut of the sRGB colour space primarily in cyan-greens

• Colour Temperature: The colour of light emitted by a object. Higher colour

temperature are blueish and lower oxddb5nes are more yellow. Measured in

Kelvin (K) after lord kelvin who heated blocks of carbon to different

temperatures to see what colour they emit.

The above is not a true colour Temperature

chart. Instead it is a hybrid, showing the colour

temperatures of light sources most commonly

encountered in professional imaging. In our

scale, tungsten-halogen has a colour

temperature of 3200°K. Household

fluorescents are accepted to be around 4500°K,

depending on the lamp. (They are shown for

reference, but would not be part of a true

colour Temperature chart, for reasons

described below).

Sunlight is 5600°K, with shade & skylight

hitting higher temperatures. These are basically

averages which became standards when they

were selected, back at the beginning of colour

film manufacturing, as the choices for various

emulsions to be made sensitive to (daylight film,

tungsten film, etc).

There are variations on these standards, but

this is a good start to understanding the

relationship between different coloured light

sources. It's important to keep in mind that

even though' reddish light has a technically

lower colour temperature, its frequently

described as warm. Bluish light, which has a

higher colour temperature, is described as

cool. In this instance, warmer & cooler

describe colour, not temperature.

• Densitometer: A device used to measure the amount of light reflected of a surface, usually used to measure the amount of ink on a paper

• Device dependent: A colour model such as RGB and CMYK where the precise colour meaning of any set of values is dependent on the device

reproducing the colour

• Device Independent: A colour model where the colour meaning of any value does not depend on any device, CIE LAB is an example (a

standard)

• Gamma: The way a device reproduces tonal values. Higher gamma values could be said to have higher contrast and lower values less contrast. 2.2

is a common gamma used in colour spaces and when calibrating monitors.

• Gamut: The range of colours and tones a device can reproduce.

• ICC: International Color consortium a group of companies who formulate standards for colour management. Companies include, Adobe, Apple,

Microsoft, Eizo

• Luminance: Basically how bright a light source is. Usually measured in candelas.

• LUT: Look Up table – a table of values that allow referencing and replacement. Monitor calibration and profiling applications may adjust the

LUT of a graphics card.

• Monitor profile: An ICC profile describing the colour space of a computer monitor. Also referred to as Display profile.

• Profile: A file format developed by the ICC to contain information about colour space of a device.

Windows keeps colour profiles in: C:\Windows\System32\spool\drivers\color

Macs in: /HD/library/colorsync/profiles

• Perceptual Rendering: A rendering intent that scales one colour space into another maintaining the differences between colours. Both in gamut

and out of gamut colours can be changed. Used best when converting images with out of gamut colours from a large colour space to a smaller one

• Relative Colorimetric: A rendering intent where colours are mapped as accurately as possible relative to the differences in white point between the

source and destination. In gamut colours are mapped very precisely and out of gamut colours are mapped to the closest in gamut colour. Good for

when converting colours here few are out of gamut of the destination

• Soft-proofing: Accurately previewing on a monitor how an image will print

Why Colour is Important

Colour is all around us. Colour is a sensation that adds excitement and emotion to our lives. Everything from the cloths we wear, to the

pictures we paint revolves around colour. Without colour the world (especially RGB World) would be a much less beautiful place.

Colour can also be used to describe emotions; we can be red hot, feeling blue, or be green with envy.

As photographers we need to be aware that what we see on our own screens is not necessarily what others will see on their screen or

when we print out our images.

So we have to keep in mind where the output will ultimately go, i.e. web, print, press.

This is why we need to manage colours from capture, through processing and to print or upload outputs.

Colour Management

We don’t need to be colour scientists to be able to successfully colour manage

our workflow, just as we don’t need to be mechanics to know how to drive a

car, but knowing something about how a car works can help us drive better.

Knowing a little of what colour is and how we perceive it will help us colour

manage our devices and deal with any problems we encounter along the way.

How We See Colour

There are three basic elements that we need to perceive colour

• Light – We need light to see colour. There are all sorts of ways to describe light, but at its basic level light is a form of radiation. A

spectrum of different electromagnetic wave lengths that that includes, X-rays, radio waves, infra red, ultra violet, micro waves and

much more. Humans can only see some of this spectrum referred to as the “Visible Spectrum/light” colours of the visible

spectrum includes: Violet, Indigo, Blue, Green, Yellow, Orange & Red (colours of the rainbow)

• Object - Most of the objects we see does not have its own light source. We can only see them because they are

reflecting and absorbing certain wave lengths of light. This dictates the colour of the object

• Observer – Our eyes turn reflected light into something meaningful.

Reflected and Emitting Light

While we see physical objects by way of reflective light i.e. grass, sea, images on

printed paper, when we are looking at our monitor we are seeing emitted light.

Light is coming from our monitor not being reflected by another light source.

We can be in a very dark room but still see our monitor and the colours it

produces, while at the same time if the room is dark enough we won’t be able

to see the colour of a green ball at the other side of the room

Why Colour Manage?

• Removes individual colour perception out of the process and standardise colour from beginning to end

• Device independent – Colour management gives us the ability to move our images from one device to another, while still maintaining without the loss of colour information.

• More control - With a well defined colour management process we have more control at every step of our photography workflow from capture, through to raw processing and then on to post processing. At any given point in this process we can convert ourimages to two or more colour spaces.

• Consistency of output to other media – If we have good colour management process we can be confident that what we see on our monitor will render correctly on other devices such as printers.

• Speeds up workflow – We colour manage to speed up our workflow processes.

• Future proof – Colour management work on a device independent basis and is standardised by the Commission Internationale d’Eclairage, so we can be sure that any future standards we will be able to use.

Colour management is not a thing, it’s a process.

Brief History Of Colour Management

• CIE commission Established in 1924

• Its intention was to create an international agreement on colorimetric specifications and updating the OSA's 1922 which was a

“standard” before 1924

• In 1931 concluded with the formalization of the CIE 1931 XYZ colour space and definitions of the 1931 CIE 2° standard

observer with the corresponding colour matching functions, and standard illuminants A, B, and C.

• In 1931 they formalized CIE 1931 XYZ colour space

• In 1964 formalized a new standard daylight illuminant D6500 was added, and created a method for calculating daylight illuminants

other than 6500K

• In 1976, the commission developed the CIELAB and CIELUV colour spaces, which are widely used today

• Based on CIELAB, colour difference formulas CIEDE94 and CIEDE2000 were recommended in the corresponding years.

Colour Management Workflow

• Begins at capture time with white balancing either with a grey card or custom kelvin value

• Get a good colour reference. Colour Checker gives us a reference point for colours under the lighting conditions we are shooting.

Also provides 18% grey white balance

• Calibrate and profile monitor

• Calibrate Camera

• Make reference changes to images in raw convertor (light room, Adobe Camera raw)

• Configure our workspace in Photoshop

• Proofing for printing

• Selecting the correct colour space for Web

• Regular profile checking

Capture

Colour checker. Used for setting in camera white

balance and provides a colour reference for

camera calibration later on in the colour

management process

Manufacturer Tolerance

Not all devices are created equally. Manufacturers of cameras, monitors printers

etc. have an “acceptable "tolerances in their manufacturing process. Two

monitors the same make and model may yield different results.

Monitor Calibration

What calibration does is make sure our device is working optimally, this will

involve us changing the monitor to a particular colour temperature, luminance

(brightness) and gamma (tone curve), some monitors will not have all these

individual settings, but we can still calibrate our monitors as the profiling step

will make allowances for this in the software.

Monitor Profiling

We profile to tell our monitors how to display colours on

our monitors. A profile is created uniquely for a monitor.

Profiles from one monitor will not necessarily give correct

colours on another monitor even if it’s the same make and

model or in a multi-monitor configuration

Colorimeters

Camera Calibration

Lightroom, Photoshop, Aperture and other image

processing software install many camera profiles, and

quite often there are more than one profile for a camera.

Generally these default profiles do a good job, but they

were not created for your camera and the lighting

conditions at the time of capture. X-rites ColorChecker

passport is a product that has been designed with raw

conversion in mind (always do as much in raw as

possible) It consists of a test target that has a grey

balance, colour references and a Macbeth colour checker

profiling target. The process of camera calibration is

very simple once you have a known colour target, you

can then load it up in to a profile maker, the profile is

created and from there you can use the same profile for

all images shot with a particular camera and lighting

condition

Printer Profiling

To profile a printer you will need a spectrometer. The X-Rite Colour Munki is a spectrometer that uses

100 colour patches to profile a printer. This device can also be used to calibrate and profile monitors.

True photographic printers are usually fairly easy to profile. Before profiling any colour management the

printer has built in will need to be disabled.

You will then need to print out a test. Then use the spectrometer to read the colour of the print out, after

which a profile for that printer and the paper will be created

The ColorChecker Creative Enhancement Target

provides absolute reference points for creatively

changing white balance, so photographers can enjoy the

benefits of creative white balance editing. Portrait

warming and landscape warming and cooling patches

help create pleasing and repeatable edits with just the

click of the eyedropper. Now anyone can attain the

truest skin tones and an accurate basis for colour

correction and editing, and apply them to multiple image

edits. Plus, the ColorChecker Creative Enhancement

target can be used with virtually any Raw processing

software.

Further Reading & Information

• Essential Colour Management: Amazon

• Real World Color Management: Amazon

• Color Management for Photographers: Amazon

• X-rite colour Checker: http://xritephoto.com/colorchecker-passport-photo

• X-rite Colour Munki: http://xritephoto.com/colormunki-photo

• DataColor Spyder 4: http://www.datacolor.com/portfolio-view/spyder4pro/

• DataColor Spyder 5: http://spyder.datacolor.com/portfolio-view/spyder5pro/