Colour Management for Beginners – Profiles Explained

Color Management for beginnersIf you are frustrated by Photoshop nagging with an Embedded Profile Mismatch every time you open an image, this document is primarily for you. If you have worked it out by trial and error, but still don’t know what on earth is going on behind the scenes, then this is still for you!

Computers don’t understand colour. A colour, to a computer, is nothing more than a collection of numbers – without soul, subjectivity or emotion. Humans on the other hand perceive colour in so many ways you would need to be a chemist, biologist, neurologist, psychologist and philosopher all rolled into one to appreciate the impact it has on our daily lives.

We most generally encounter man made colour in two fundamentally differing ways:

  • On electronic display screens (computers, phones, TVs, cinema etc) where the colour is the result of projected or emitted light
  • In printed forms, where the colour is a result of pigments, dyes or whatever else is placed on the printing surface (substrate)

RGB colour

RGB Additive ColourRGB colour is what you are most likely looking at right now (unless you have printed this page on paper!). RGB colour is made up of Red, Blue, and Green light. Where colours mix, their waveforms merge to create secondary colours.

Computers generally display colour onscreen using a pallette of 16.8 Million colours.This number is not arbitrary. It is the result of each component colour (red, blue, green) being represented by any value from 0 (black/off) to 255 (brightest/on), and 255 x 255 x 255 = 16,777,216!

RGB colour can also come in 16bit flavours – where each component is represented by 65,535 levels of brightness, far more resolution than the human eye can perceive – the advantage of using such a deep colour system is that editing, filtering and manipulation can take place without loosing perceptual image quality in the end result.

CMYK color

CMYK Subtractive ColourCMYK colour is what you are most likely looking at when you read a magazine or most other things that are printed on a commercial press. CMYK colour is made up of four colours – Cyan, Magenta, Yellow and Black. Each component colour is represented by a percentage from 0 to 100. This provides an even larger number of colour combinations than RGB.

Just as RGB has it’s supercharged 16bit cousin, so CMYK also has other more exotic flavours, such as Hexachrome, and CcMmYK which provided a broader colour gamut by using more inks. Gamut? Eeek! What’s that?

Colour Gamut

OK, so now we have a basic understanding of how colour is produced on screen and in print. Perhaps the next thing to appreciate is something called Gamut. There are many articles regarding Gamut that go into incredible technical detail and use the most groovy of diagrams, one of which I have included here. However, this can quickly lead to cranial meltdown, so I’m going to attempt a simple conceptualisation – which is all we really need at this stage.

CIE 1931 Colour Space DiagramImagine a global absolute system of measuring colour. Well, the people at the International Commission on Illumination created one as far back as 1931, called the CIE 1931 color space. This system was important because it finally produced a yardstick by which to measure colour as perceived by the human eye – rather like the Metre rule as the standard unit of measurement. The CIE system uses three specific wavelengths of light for red, green, and blue – and specific formulas for radiant power and luminosity. The result is a standardised measurement of colour.

The human eye can perceive an incredible range of colour. Far more than we can reproduce using a computer screen, or in print. The diagram opposite (based on the CIE 1931 colour space), shows how the gamut of some common colour systems measure up to what the human eye can perceive.

Imagine a rainbow. Pretty ain’t it? Now, imagine seeing a picture of a rainbow printed in a book. Not quite as vibrant is it? This is because the colours that are projected from a real rainbow are outside the gamut of the CMYK colour system. Likewise, there will be colours that can be reproduced on your computer monitor or TV, than simply aren’t possible using CMYK (for example, vibrant orange colours are particularly difficult for CMYK).

Conversely, there are some colours (although admittedly not many) in the CMYK gamut that exist outside of what a standard computer monitor can display.

Introducing Colour Profiles

A Colour Profile is a way of describing how a particular system displays colour. Arguably, every individual device requires a colour profile in order to display colour accurately. Just go to your local high street electronics store and look at a row of TVs showing the same movie – the colour differences will be obvious! This is because your average TV set (or computer monitor) is not accurately calibrated.

This is where we get to the nub of the problem, and where people tend to get confused. Colour profiles can be split into two distinct groups. Those which are independent of any display device, and those which are device dependent (whether that is your flat panel monitor, or a commercial printing press weighing several tons).

Device Independent ProfilesDevice Independent Profiles

Some profiles, are really colour spaces in their own right. sRGB, and Adobe 1998 are two common examples. However, basically speaking, they are just different ways of describing how to convert CIE colours into RGB values. sRGB is widely used in the TV industry (also the standard for the web), and Adobe 1998 being widely used in Photography due to it’s broader gamut.

In the print industry, the FOGRA27, Europress and SWOP CMYK profiles offer standardised gamuts for CMYK printing based on various standard print processes.

Device dependent profilesDevice Dependent Profiles

Going back to our TV sets, and computer monitors for a moment. It should, in theory, be possible to calibrate all of those TV sets so that they display the same colours. This would be a device dependent profile, and it would be different for each and every TV set (even between examples of the same model).

Your inkjet printer, for example, probably has it’s own factory standard profile to allow it to print reasonable photographs. If you wanted things to be super accurate, then you could calibrate your printer with a custom profile, produced by printing a test image, and then inspecting that image under a colorimeter. All these things cost money, so you can see why most people don’t bother!

So as you can see, almost every system of colour reproduction in the world can be given a colour profile to describe how it can best duplicate the colours in the standardised CIE Colour Space.

If we have a mathematical way of describing how every colour system should work with reference to the CIE standard colour space, then it is just a case of some further maths to work out how to convert the numbers from one colour system into another.

Bringing it together

A colour managed workflow relies on three components:

  • Devices (screens, printers, scanners, cameras)
  • Profiles (device dependent and indedpendent)
  • Conversion engine (to carry out the conversion from one profile to another – e.g. Adobe ACE, or Apple CMM.)

In order to match the colours from one system to another, you must have two profiles – the source profile, and the target profile. The diagram below shows a typical scenario, where a designer is working on a design in CMYK mode.

Colour Managed Workflow

In order to view the colours accurately on-screen, a calibrated monitor is used. Calibration is achieved by using something called a Spyder, which is basically an electronic eye that is attached to the monitor and works in conjunction with supplied software to create a custom colour profile for the monitor. That way, the designer can see a fairly accurate representation of the final artwork on the monitor. This is because the Conversion Engine has converted from the device independant CMYK profile (FOGRA27 in this instance), to the device dependant monitor profile created by the Spyder.

Likewise, when the finished job is sent to be printed, the embedded FOGRA27 profile is again converted by the commercial printer’s RIP (Raster Image processor). Using their own conversion engine and device dependant profile for their large expensive press, the RIP creates the final ink separated plates that put exactly the right amount of inks on the paper to produce the expected results – in theory!

So, provided we have a source profile, and a target profile, we should be able to reproduce colour consistently between an infinite number of devices.

In practice

Meanwhile, back in the real world, most people are not very colour critical. A common issue I encounter are customers who question the colours in electronic PDF proofs. Even when I have used an agreed CMYK colour from a pantone book, the customer thinks it doesn’t look right on their £300 laptop from PC World.

Although I re-profile my monitor every month or so, the displays on my customers’ computers are rarely profiled (and some are of such poor quality, it wouldn’t improve matters greatly if they were profiled). I don’t want to sound harsh, but hopefully this will explain why things often don’t look right on screen, and why printed proofs are often a better idea – as opposed to choosing your print colours based on the output from a cheap laptop screen! However, there will still be a slight difference between digital proofs and the final lithographic output. The secret here is not to become overly obsessive about colour accuracy unless you have deep pockets!

Even a perfectly calibrated monitor is not going to match exactly what is printed on paper – if you are viewing your printed material under dim tungsten lighting, for example. I’m not saying that colour management is a waste of time – far from it. A colour managed workflow is crucial in producing consistent results, especially when you are dealing with multiple input and output devices. Just be realistic, and keep learning!

Few are prepared to pay the price for super precise colours, and I know many designers who don’t bother either. I can understand this to some extent, when working in certain markets. Plus, there is always some difference between source and target. Hell, if you send the same job to the same printer a few weeks apart you will get slightly differing results. Humidity, temperature, ambient lighting, all play a part in how ink will behave, and how the final colours will appear. I have two Pantone process swatch books in my desk drawer, and even they aren’t the same (although one is 2 years newer than the other), despite being kept in darkness. Go figure!

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