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The facts

The pixels in LCD panels work by passing polarised light through filter layers. To light up a pixel, the liquid crystal component in each pixel applies a ‘twist’ to the light after it passes through the first polarising layer, making it able to pass through the second. Unlike CRT displays, where what you see is caused by the phosphor coating inside the glass tube being excited by electron beams, the light emitted from an LCD screen makes its way through multiple layers, channeled out through each pixel. This is the root cause of this technology’s biggest Achilles’ heel: view an LCD screen from straight on and you’ll see each pixel exactly as intended. But view it from far enough to one side - or above or below for that matter - and you won’t get the direct, face-on strength of the light beaming out of the pixels. To use a very crude analogy, it is a little like the difference between viewing a light at the base of a tube from face on or from off to one side. Only one viewpoint gets the full strength of the light as it shines out. The result is changes in the values of what’s shown on the screen depending on where you sit. This is clearly a disaster for colour proofing, and something that no amount of calibration can help.

This problem has plagued LCD manufacturers for years, but the situation has improved immensely. The best modern LCD panels have all but eliminated this problem. Note the qualifier: the problem still exists, but at the top end of the market it is effectively negligible. Most decent modern displays are dramatically better than models from just a few years ago. In today’s desktop LCD screens at least you’re unlikely to see colour and contrast inversions just by leaning to one side or looking down from a standing position, but you will still see a slight shift in hue and contrast if you move far enough away from straight on to the display. The problems now tend to show themselves as a minor contrast drop and a faint yellowing of whites instead. How far you have to move to see this is as critical a point as how much change there is, which is why most manufacturers give viewing angle specifications for their monitors. It is common to see figures of 140° or more, but this will bethe point at which the display shows obvious, unmistakable changes rather than where visually critical users might first spot colour drifts.

Older LCD screens had such a narrow field of view that merely leaning over a bit or just sitting up straight in the chair would produce obvious visual changes. This isn’t the case with newer displays, but it is worth noting that if you sit quite close to today’s larger panels your angle of view from one side to the other and from top to bottom can be great enough to produce colour shifts in objects simply though being in different parts of the screen. Although LCD technology is constantly improving, the increase in display sizes tends to make this somewhat of a ‘two steps forward, one step back’ situation, particularly with the very largest LCD panels now on offer. For example, despite using the the very best quality of LCD hardware available, this effect can still be seen in Apple’s 30in Cinema display. Making sure you sit at a reasonable distance from your screen can help reduce or even eliminate this, but it is something to remember if you do critical colour work on your Mac.

Finally, make sure you keep everything in perspective. This shouldn’t be seen as a reason why you should stick with your old CRT if it is getting a bit long in the tooth. The unstoppable problem of phosphor aging means that CRTs will loose sharpness and brightness as time goes by, and a top-quality LCD will always beat all but the best CRTs.

ColorSync and colour management

Calibration of LCD screens can’t be performed to the same degree as with CRT displays, but the best way to manage colour lies more in the use of a well-managed colour workflow. Use calibration hardware such as the Eye-One from GretagMacbeth to produce full, accurate ColorSync profiles from your monitor’s display characteristics, then use those to define your display as part of your ColorSync settings. Once in place, ColorSync will manage how images are shown on that display, adjusting the presented appearance according to the particular slight variances in colour presentation that the profile lists.

If you don’t have a hardware calibration device you can actually perform a limited calibration to produce a ColorSync profile with nothing but software and your own eyes. In the Displays pane in System Preferences, click the Color tab, then the Calibrate button and walk through the simple producess. After making a few selections with sliders you can save and then select your new profile. Alternatively, SuperCal from bergdesign.com provides excellent display calibration including corrected gamma tables. Whichever route you choose, whether hardware-based or performed entirely in software, having an accurate ColorSync profile created specifically for your monitor is one of the keys to an efficient colour workflow.

Further info

You can find out more about these issues from numerous sites, including the Pro-face Technical Information pages for more on the viewpoint issues, and moebius.physik.tu-berlin.de/lc/ for a technical explanation of LCD pixel characteristics.

The SuperCal shareware calibration software can be downloaded from the SuperCal pages at the Bergdesign site, and comes in versions for Mac OS 9 as well as Mac OS X.