Deep Dive: Colour management
Hankering for true blues and rich reds? Darien Graham-Smith explains how colour profiles can help you get the best from your display
You don’t need a degree in ocular biology to make the most of your monitor. Darien GrahamSmith explores the vivid world of colour profiles.
Colour management is easy to describe: it means accounting for differences in display and printer hardware, and compensating for them, so that colours come out looking the same on every screen and printer. So far as is possible.
What’s more complicated is the mathematics that underpins all of this, which involves some dauntingly complicated formulae that draw in aspects of both physics and ocular biology. Happily, you don’t need to fully understand the theory to take advantage of colour management: in this Deep Dive, we’ll introduce you to the key concepts and tools you can use to get your display looking as good as possible – or as accurate as possible, which, as we’ll see, isn’t necessarily the same thing.
Why do we need colour management?
Modern computer screens all work in the same basic way – by mixing together red, green and blue light to produce a whole spectrum of visible colours and shades. Beyond this, though, it’s not much of an exaggeration to say that no two screens are wholly identical. Different devices use different methods of illumination, different arrangements of coloured subpixels, different backlights and so forth. As a result, if you look at the exact same image on two different screens, you may see a clear difference in colour tone and contrast – and it won’t necessarily be obvious which one is “right”.
For most of us, this isn’t a calamity. Even if a screen has a slight colour cast, you can still work and browse the web on it. However, if you want to watch movies then poor colour reproduction can detract from the experience. And, if you’re creating artwork or videos, you can’t afford to use a screen that misrepresents the colours you’re using.
This is where colour management comes in: it allows us to apply display-specific corrections to the colour values that are sent to the monitor, to bring the colours as close as possible to consistent, standardised shades. This might, for example, mean tweaking the intensity of the red, green and blue components so that grey shades come out looking balanced and neutral, while big blocks of colour aren’t spoilt by understated blues or overexcitable greens. With this done, you can be confident that when you edit a photo or put together a video clip on your monitor, it will look broadly the same on someone else’s screen.
You’ll notice that we say only that graphics will look “broadly” the same, and there are two reasons for that. First, there’s no guarantee that the person viewing your creation will themselves be using a colour-accurate display – but there’s nothing you can do about that.
The other thing to remember is that all computer monitors have physical limitations, and that applies especially to low-cost desktop displays. If your red LEDs have a slightly orange tint, no amount of digital correction will allow your screen to produce the purest, richest scarlets and maroons.
Running the gamut
This brings us onto an important technical term: the colour gamut. This is what we call the complete range of colours, of all shades and hues, which a screen or printer ought to be able to produce. A few different gamuts are used in the industry, but the one
you’re most likely to run into is sRGB, short for “standard red, green and blue”. Jointly created by Microsoft and HP back in 1996, sRGB has become the de facto standard for personal computing, and if two applications or devices are sRGB-compliant then colours within this palette should appear consistent across them.
That’s the theory anyway: to reiterate, no monitor is perfect. That’s why, when we review monitors, we use dedicated colorimeter hardware to measure exactly what proportion of the sRGB gamut the panel can produce. If a display has only 80% sRGB coverage, that means it’s incapable of accurately producing certain shades – even with corrections applied. A display with 99% coverage will have no such problem.
This coverage rating isn’t to be confused with colour volume. This reflects the total range of colours that the display can produce, including those that lie outside of the sRGB gamut. As we’ve noted, sRGB was originally defined in the age of CRT monitors, and today’s displays can do a better job of rendering the most vivid colours – so a modern high-end display might boast a colour volume of, say, 110% of the sRGB range.
To take advantage of these capabilities, the slightly newer Adobe RGB gamut extends to include richer colour gradations than sRGB can represent, notably among the green and blue hues. The gamut diagram overleaf illustrates the complete range of colours our eyes can perceive, with the inner blue triangle representing the sRGB gamut, and the larger red one representing Adobe RGB.
Adobe RGB can be useful if you’re producing media that’s intended to be viewed on a professional display or a cinema screen; “prosumer” cameras and camcoders often give you the choice of shooting in either sRGB or Adobe RGB. If you’re tempted to give it a try, though, be warned: as we’ve mentioned, sRGB is the consumer standard, and few web browsers and applications will correctly render Adobe RGB media, resulting in your images looking duller and darker than intended. We recommend you stick with sRGB – which is good enough to provide spectacular results on a decent screen – and leave the bigger co lour spaces to the professionals whose entire workflows are optimised for them.
Before moving on, there’s one last point to note: even if a display is technically capable of covering the entirety of the sRGB spectrum, that doesn’t guarantee that every shade will look exactly as it should. This is where the mysterious Delta E measurement comes in. The name derives from the symbol for difference, plus the German word
Empfindung, which can be roughly translated as “feeling”, and it simply gives a numerical value to the difference between the colours produced by a display and the shades as defined in the gamut. The measurement is calibrated so that one is the smallest difference the human eye can distinguish, so a display with a Delta E of less than one is effectively perfect. Since not many such screens exist, we recommend a display with an overall Delta E of two or lower for professional colour-accurate work.
Colour profiles
We’ve talked about applying corrections to the video signal that’s sent to the monitor: how exactly is this done? The answer is with colour profiles. These are little files that tell Windows (or a specific application) about the capabilities of your screen, and define the adjustments that need to be made to obtain the most accurate output. There are two common formats for these: ICC (International Colour Consortium) and ICM (Image Colour Management) files. The former was originally developed by Apple, while the latter is native to Microsoft, but nowadays both Windows and macOS can use either type.
If you’re using a popular consumer monitor, or a laptop that came set up from the manufacturer, the appropriate profile may be already installed. You can check this by searching the Start menu for “Colour management” and opening the Control Panel item that comes up.
(The fact that Microsoft still hasn’t migrated these controls into the Windows 10 Settings app probably reflects the fact that colour management isn’t something the average user cares about as much as they should.)
When the window opens, the Devices tab will be open by default, and you should see your default display selected at the top – if it’s not, click to select it from the dropdown menu. In the big pane below you’ll see a list of profiles that are “associated” with it. In theory, you can assign as many profiles as you want to a device; for example, you could have one profile for working in daylight and another for nighttime viewing under artificial light. This really is something that only serious professionals need to worry about, though.
The important question is whether a profile for your precise monitor model is already listed. If it is, you don’t need to do anything more – although you might still prefer to calibrate the monitor yourself, as we’ll discuss below.
If the list is empty, or shows the wrong details, then you’ll want to add a profile. Start by checking the website of your monitor or laptop manufacturer, to see if a compatible one is offered for download. Bear in mind that the colour profile might be bundled up as part of a bigger display driver, in which case it will probably be automatically applied as part of the installation routine.
If your download is a bare ICM file, you can install it by clicking the tickbox labelled “Use my settings for this device”, then clicking the “Add…” button. You’ll see a list of profiles that are already installed on your system; these are mostly intended for print and won’t apply to your monitor, so
click “Browse…” and select the file you’ve downloaded from your manufacturer. Once it appears on the profile list, click on it, then click “Set as Default Profile” – and get ready to enjoy more consistent colour.
Creating a colour profile
If you’re not happy with the official colour profile for your monitor – or if you can’t find one – you can always create your own. This isn’t hard, but there’s a catch: it’s impossible to tell just by looking whether or not your display conforms to the defined colour standards. To create your own sRGB profile, therefore, you’ll need to invest in a dedicated colorimeter that can accurately measure and analyse the colours your display is producing.
These cost around £150, and if you’re serious about image quality are a worthwhile investment. Any X-Rite colorimeter will do the job, but search out the X-Rite ColorMunki Smile on eBay (it’s been discontinued) as it comes with software that puts your monitor through its paces and calculates the appropriate corrections to generate a custom ICM profile.
If you just want to run a one-off calibration on your personal monitor, however, the price is harder to justify; consequently, you might opt simply to trust your eyeballs and set things up so they look as good as possible to you. If you take this route you may end up with tones that look quite different to those targeted by content creators.
But if your desktop is drab and cold, a spot of tweaking can give you livelier colours, weightier text and a more enjoyable visual experience overall – even if it’s not colour-accurate.
The Windows colour calibrator
Your graphics card driver may well include settings that you can use to adjust the colour and tonal balance of the display, but the simplest option is to use the colour correction tool that’s built into Windows. You can find it by searching the Start menu for “Calibrate display colour”; the process is actually rather more subjective than the name implies, but it’s the one that Microsoft has chosen.
On launching the tool, you’ll see a grey screen explaining what’s about to happen. Click Next to move onto the next step and you may find that your screen colour abruptly changes: any previously applied ICM profile will have been switched off, ready for you to start creating a new one. (Don’t panic: if you’re not sure about your new settings, you’ll have the option of restoring your old profile at the end of the process.)
Now comes the first part of the calibration process – setting the appropriate gamma correction levels. Simply put, gamma means the balance of dark and light tones: if your gamma correction factor is too low, the image will be skewed towards darker shades, while higher values give a brighter, overexposed appearance. As with colour reproduction, you will want to get the correction factor right so that your monitor displays a good even spread of shades.
The Windows tool uses what is basically an optical illusion to help you find the balance, with an image of nine circles made up of lines of light and dark pixels. By pulling the slider up and down, you can adjust the tonal balance so that the areas of alternating black and white pixels have the same visual intensity as the mid-greys around them. Once they look the same, that should mean you have a nice even tone curve. However, since we’re not aiming for perfect colour accuracy anyway, you’re not obliged to keep it perfectly balanced: personally, I find that pulling the gamma slider down just a little bit farther helps ensure that text and interface elements look sharp and solid.
Next, you will be prompted to find the ideal brightness and contrast settings for your monitor. You can skip this step if you’re using a laptop that lacks specific controls, or if you just don’t want to bother with it. If you go ahead, you’ll be shown close-ups of two rather ropey photographs (which haven’t been updated in more than a decade), and prompted to adjust your brightness settings so that the murkiest details are visible, then to set your contrast so that lightcoloured detail isn’t lost.
With that done, it’s finally time to get to grips with your colour balance. You’ll be shown a series of five grey bars, and invited to adjust the relative amounts of red, green and blue light until the bars look perfectly neutral. You’re free to play with the sliders however you like, but we have two warnings. First, you can only reduce the intensity of the individual component colours, not increase it: if you pull all the sliders to the left you’ll be left with quite a dim display. Try to find a good balance with one slider at maximum, and the others pulled down only as far as they need to be.
Second, don’t underestimate the ability of the human eye to quickly get used to things. Once you’ve found a setting that feels right, go away and look at something else for two minutes. When you come back, you may well find that your settings have a jarringly obvious colour cast that you didn’t notice at the time. It’s worth taking some time to get this right, and perhaps switching into other applications to see how your settings look in other contexts – because, annoyingly, Windows won’t let you make tweaks to your colour profile once you’ve created it. All you can do is create a new one from scratch.
Once you’re happy with your settings, click Next one final time: the final page of the calibrator tool gives you a pair of buttons that you can use to compare your new profile with your old one (or with no profile, if you weren’t previously using one). Be warned that if you click Finish at this point, your old profile will be overwritten by the new one; you won’t be asked if you want to keep a copy of your previous profile. However, nothing stops you making a backup of it yourself before you hit the button. To do this, simply open the File Explorer and navigate to the folder where Windows stores its ICM files, which is normally: C:\Windows\System32\spool\drivers\color
You’ll find your old profile here – it will have a name such as CALIBRATED DISPLAY PROFILE -0. ICC
– along with the new one, which currently has a “TEMP” suffix. Before you close the colour calibration tool, make a copy of it with a new name; if you later decide you want to revert to it, you can reapply it from the Colour Management dialog.