• Features

• 27/11/2015

Understanding, managing and calibrating colour is key to display consistency and quality. Klaus Bjarner, sales manager at Datacolor Europe, explains.

Glossary
When reading about colour management don’t let technical terms you are not familiar with put you off.

Gamut
The gamut, or colour gamut, of a certain output device is that portion of the colour space that can be represented, or reproduced. When we are talking about the gamut of a monitor it is most commonly in reference to the AdobeRGB colour space, and to what extent the monitor can reproduce that given colour space.

Colour space
When colours are displayed on a computer monitor, it is from a combination of red, green and blue. Think of the colour space as a bucket of colours. The bigger the colour space, the more colours it can contain. When we are defining a specific colour from a combination of red, green and blue it is always in reference to a specific colour space. Since a computer works in 8-bit we only have 256 steps in each colour channel when mixing a colour from red, green and blue. Because the maximum amount of a given colour varies depending on the common colour spaces; sRGB, AdobeRGB and ProPhoto RGB; a colour (RGB combination) gives no meaning unless it is referring this value to a given colour space.

Colour temperature
Colour temperature is a characteristic of visible light and is usually measured in kelvins (K). Higher colour temperatures (5,000K or more) are cool (blueish white) colours, and lower colour temperatures (2700–3000K) warm (yellowish white through red) colours.


Why spend time on calibration and colour management?
Colour management is the process of ensuring that colours are true and consistent throughout the entire workflow, from capture to edit to final display. Every display has its own gamut. Even two displays of the exact same brand, model and age will have variances in gamut. Having colour calibrated on your equipment provides consistency and ensures you have the correct colours on each device within their gamut.

In colour management, the colour displaying characteristics of each device are mapped to an ICC profile, which is the colour fingerprint of the device. When a computer operating a system reads the ICC profile it knows exactly how the device reproduces colours and the gamut and can compensate for colour casts and other variances. This means the colours are displayed correctly. The most important step is calibration of the displays. This is the first place we see the digital file, and it is on that basis we decide if the colours are correct or need adjustment. Therefore, it is crucial that what we see is correct.

Carrying out calibration
Only a few years ago display calibration was a task only performed by highly specialised professionals. Today, thanks to easy to use display calibration systems, profiling a display is easy.

Most calibration systems consist of a measuring hardware and a software package, that guides you through the calibration process step by step. During the actual calibration process the hardware (an electronic eye) is placed in front of the display. The software then displays a range of colours which are measured by the hardware. These readings are then compared to the actual data sent to the display. The difference between the two, is the inaccuracy of the display. A display can then compensate for the discrepancy. This ensures that the display shows the correct colour, and you see a 100 per cent accurate reproduction of the colours.

The calibrator unit does not just measure one colour, because a display’s colour cast is not necessarily consistent through out the entire colour spectrum. It might display too much red in the dark green colours, and too little when displaying bright green. So to ensure a perfect calibration it measures several shades of each of the primary colours - red, green and blue. In addition it also measures shades of grey including black and white level.

Reaping the benefits
Having calibrated the monitor we now have the benefit of a display without colour cast, but we also achieve two more significant benefits. First of all adjusting the display for colour casts also gives us the correct contrast of the display and the gamut which is stored in the ICC profile.

When broken down to basics, display calibration is just a matter of mapping how the device displays colour, by measuring the build in variances. When variances are known they can be compensated for, thereby achieving true and accurate colours on the display.

Maintaining calibration
Calibrating your display once is unfortunately not enough to ensure consistent colours forever. Due to the way a display is constructed the colours change over time. This can be due to backlight degradation that slightly decreases the brightness of the display. To ensure 100 per cent accurate colours it is necessary to calibrate a monitor regularly.

More info
The content on this page was provided courtesy of Klaus Bjarner, sales manager at Datacolor Europe. For more information about monitor calibration and which tools to use visit www.datacolor.eu