Basic setting up

A good picture rendition can be simply achieved by the installer or user in a short time. Start by switching to normal mode as opposed to ‘Turbo’, ‘Sports’, ‘Dynamic’ or whatever, and ensure that image enhancement features – they go by many names – are switched off. Set the brightness and contrast to about 60% each and the sharpness and tint/hue controls to midway point or 50%. Turn the colour/saturation fully down – thus off. Now, in a low ambient light, adjust brightness to the point where the darkest part of the picture is just black. Reset the contrast so that the brightest picture features are comfortable to view in the ambient light level normally present in the room. Set the sharpness control for best detail rendition without noticeable grain or ‘grass’ and – still with the colour turned fully down – adjust the hue/tint setting to give neutral white and grey tones, neither warm nor cold looking. Finally wind up the colour so that people's faces, in a studio shot, look normal and healthy. That’s it, in a nutshell. The use of a test-pattern disc like Digital Video Essentials from JKP makes the job easier and more accurate.

Professional calibration

A professional screen calibrator goes much further than this. He sets the user controls mentioned above in the same way but with much more precision. For this, and the other necessary adjustments the following equipment (representing an outlay of some thousands of pounds) is used: a spectrophotometer and tristimulus calorimeter, light/colour analysers looking at the screen; special pattern generator; DVD and Blu-ray pattern generator discs; a laptop PC running purpose-designed software by, for example CalMAN or Chromapure; and for some TVs a special service-type remote control. Using the service/factory set-up menu, not accessible to users, he is able to reset the operational software of the colour processor and screen-drive circuits to get their operation as close as possible to perfection.

Red, green and blue primary colours are set to the correct points in the CIA chromaticity triangle to achieve optimum colour reproduction. Red, green and blue drive levels are equalised at several points across the grey-scale range to eliminate tinting and hue errors at all brightness levels. The white point of the picture is set to the industry standard of Illuminant D6500, corresponding to the colour temperature of TV studios and film sets: it equates to scattered daylight in a northern sky. And the gamma of the screen image is likewise optimised to the broadcaster/film-maker’s specification. Gamma is the relationship between light into the camera and light out of the viewing screen across the whole range of brightness levels; incorrect gamma setting stretches or compresses brightness steps at extreme light levels. Other aspects of the TV’s CMS, Colour Management System, are also addressed and optimised.

The calibrator's settings are written to memory and permanently stored there by the use of the TV’s remote control. Some late TV models are very calibrator-friendly in having direct access, via USB or other interface, from the set-up computer to the TV memory chip, greatly reducing the (typical three hour) set-up time. Calibrators usually charge the end-user about £300 for the service, more for out-of-area calls.

Peripherals

Other equipment in the home-cinema orb is also amenable to calibration: of course projectors, but also video disc players and surround-sound processers; they are also checked for wiring, matching and phasing errors. Some calibration companies also offer equipment-specifying and -selection services, and installation of home cinema gear. The reference and standard-setters for audio are Dolby and THX; and for video, ISF (Imaging Science Foundation) and THX, standing rather quaintly for Tomlinson Holman's Xover.

Results

Is TV calibration worth the trouble and expense? It depends on the viewer's aspirations and perception. Certainly the picture quality and fidelity can be vastly improved for those with eyes to see it,  and calibration can even reduce energy consumption and extend screen life.

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