Understanding colour spaces
Adjusting your monitor according to a single printed image will bring its colours into line with that particular printer, but it doesn’t guarantee that your images will appear on other people’s screens in the same way as they do on your system, nor that they’ll look identical on all printers. To achieve this, you need to be aware of colour spaces.
A colour space represents all the shades of colour available to a device. The two colour spaces you’re most likely to come across are sRGB (standard red, green, blue) and Adobe RGB. Of the two, Adobe RGB offers a wider gamut, which is to say it can represent a wider range of shades. When you shoot JPEG images on a DSLR camera, you’ll normally have the option of using either the sRGB or Adobe RGB colour spaces. Depending on which you choose, the colours seen by the sensor will be encoded in slightly different ways. (If you shoot in RAW mode, the camera uses its own, far larger colour space, and leaves you to perform your own conversion when you process the image.)
Mid-range monitors lit by CCFL tubes rarely display the full range of colours in the Adobe RGB space (high-end LCDs, especially those with LED backlights, can produce a wider gamut). However, if your monitor is correctly calibrated and your editing software understands which colour space was used to encode an image, you should see a reasonable onscreen approximation of the appropriate colour. Mid-range and high-end printers are also normally designed to support a wide gamut, so it makes sense to use Adobe RGB for images you want to print.
If you want to share your images online, it’s a different story. Most web browsers ignore colour-space data and assume your images should be shown as sRGB. This can cause them to look subtly wrong: for example, the Adobe RGB space offers a smoother transition from yellow to green than sRGB. If you view an Adobe RGB image using the sRGB colour space, the contrast between these colours will appear exaggerated.
To add to the confusion, most mid-range and high-end printers can produce colours not covered by either the Adobe RGB or sRGB colour spaces. It’s therefore possible that your images will contain shades of colours that are indistinguishable on your monitor, especially if you work in the ultra-wide ProPhoto RGB colour space favoured by Adobe’s photographic software. In most cases this won’t produce unpleasant surprises when you print, but if you’re concerned about the detail it’s worth producing colour proofs before committing to expensive, large-format prints.
A final word to those looking to produce books or other unusual formats: print services will sometimes expect you to provide images in CMYK format, in which colours are produced by combining cyan, magenta, yellow and black ink. CMYK represents a much smaller colour space than sRGB and Adobe RGB, so colours from your original image may need to be “clipped” to match those within CMYK’s gamut. Applications such as Photoshop allow you to soft-proof your images using different colour spaces, and can warn you if large areas of your images contain out-of-gamut colours.
What are ICM profiles?
After calibrating your display, your settings will be saved as a “profile” – an ICC (International Color Consortium) or in Windows an ICM (Image Color Management) profile. The two are largely cross-compatible. Windows Vista and 7 also support a proprietary Microsoft format called WCS (Windows Color System).
A monitor profile specifies how the colours and shades described in an image file should be sent to your monitor to ensure they look correct when displayed. For example, if your monitor produces unusually weak-blue shades, a suitable profile would tell the operating system to compensate by boosting the blue content of the picture it sends to the display.
Calibrators measure ambient light as well as your monitor’s colours, so you can see whether your environment is too bright or warmly lit.
Printers also have profiles, althoughmodels aimed at home users don’tnormally come with tools to calibratethem. Just like monitor profiles, theseprofiles tell the software how toproduce colours that look as intended.
With the right monitor and printerprofiles, colour hues should lookidentical whether you’re viewing themon screen or on a physical print-out. Ifyou use an inaccurate ICM profile – oryou don’t create one at all – coloursmay be lost or mistranslated, resultingin wonky prints.
Correctly setting up your monitor istherefore essential if you don’t wantto waste time and money on sub-parprints. And getting your screen onthe right track is quick and easy. Evenprofiling your monitor using dedicatedhardware is reasonably cheap (seeHardware calibration, above). If youwant to get the best from your digitalphotos, there’s no reason not to do it.
NEX PAGE: Step-by-step guide to profiling your monitor with Windows 7.