Articles and whitepapers

Calibrating Video Displays (6/2/2006)

By Piers Clerk, Home Cinema Engineering

Video displays, whether they be televisions, plasmas, LCD display panels or even projectors, must be one of only a handful of products that manufacturers quite deliberately allow to leave the manufacturing plant incorrectly adjusted for use by the purchaser. A bold statement perhaps, but one that is generally true - and they do it for a reason.

The vast majority of video displays are sold through multiple retailers, with the competing makes usually lined up, one alongside the other, and more often than not, displayed under intense strip lighting. Research has shown that the average customer is drawn to the display that looks the 'brightest', so not unsurprisingly, the manufacturers send their products out of the factory configured to look as bright as possible.

Get this product home and the settings that made it look good in the showroom are totally inappropriate for the probably much more subdued lighting of a domestic environment. There is one other trick that the makers employ to tempt buyers to choose their product - make it blue. Remember the Daz advert from the 1970s? 'Blue Daz washes whiter'! Sure enough, adding blue to white does make it look brighter.

So what is the problem?

White balance is carefully set on a video camera before shooting begins, and similarly, when film is converted to video via the telecine process, white balance of the video monitors is also critically important. These monitors are regularly tested and calibrated to the industry standard of 6,500 Kelvins (commonly known as the D65 reference). While it is up to the director and cinematographer to use their artistic licence to establish the 'colour mood' of any film, the goal of the telecine process is to convert, as accurately as possible, that vision to video.

If viewers of the movie are to see it as the director intended, then the display device must be set to this same colour temperature. 'Out of the box', the display will very rarely be anywhere close to this desired colour temperature, precisely because of the factors mentioned above.

Almost more fundamentally, the familiar 'user controls' of contrast, brightness, colour saturation and sharpness will probably be hugely mis-calibrated for use of the display in a domestic environment. The better retailers may well recalibrate the display before it leaves their premises, and a custom installer will surely do so at the customer's home.

Controls that used to be hidden away in service menus are increasingly being found in user menus. The explanations as to how to set these controls can usually be found in the user manual, but in reality, without test equipment, the job is all but impossible. Now that they are in the user manual, the likelihood of the customer asking awkward questions about them has dramatically increased. Knowing what they do and how to optimise them, has now become more important than ever.

ISF calibration

Establishing industry standards and providing training in calibration techniques has been championed by the Imaging Science Foundation, based in Florida and headed by Joel Silver. ISF calibration is now well-established in the USA, and thanks to several training courses having been run in Europe, the concept is gaining hold in the UK. Manufacturer suspicion of the benefits of calibration also appears to be a thing of the past, and it is notable that the Pioneer 6 series plasmas and higher-end Runco projectors now include dedicated 'memory blocks' for ISF day and ISF night settings which can only be accessed by ISF-trained calibrators.

An ISF calibration is essentially a calibration, to industry standards, of the display device in order to optimise the performance of the display. Setting the user controls to perfection ensures that no detail in the image is 'crushed', no artificial sharpness is added to the image, and colours are fully saturated and accurate.

Test patterns make the job of accurately setting the basic controls far easier than doing it by eye, and these are supplied either from a calibration DVD or from a signal generator which enables patterns to be sent to the many different types of input, including high definition inputs. A colour analyser is then used to measure the primary and secondary colours, and adjust them as necessary.

The colour analyser is designed to mimic the human eye and will usually consist of a probe which is attached to the screen (as shown in the picture below) or mounted on a tripod for projection systems. The probe is attached to a computer and with suitable software the colours contained within the test patterns can be analysed.

Calibrating a Pioneer plasma for the ISF memory

The grey-scale is also measured and the amounts of red, green and blue that are contained in a 'white' picture are adjusted to meet the standards, with the ultimate goal being a 'neutral' grey-scale from black to white with no colour 'shifts'.

Screen shot from a calibration session showing that both red and blue settings still need to be increased marginally

The colour analyser is normally attached to a laptop computer which will be running graphical software that enables 'before' and 'after' calibration reports to be produced. Once analysis and adjustment is complete, the customer should not only have an optimised picture on screen, but a printed report showing that the job has been well done.

Screen shot of a typical colour temperature report showing values before and after calibration - part of a full report that proves the job has been well done

All display types can be calibrated, and costs typically start at about £250, rising according to the complexity of the display and the number of inputs and signal types that are to be calibrated. A simple calibration can take up to 3 hours but a high-end projector calibration may well take several days.

Conclusion

Properly-calibrated displays mean contented customers. They are seeing all of the image, displayed how the director and cinematographer intended. Additionally, their display device will typically last longer when run on calibrated settings.

Setting up as a calibrator does not come cheap: a full package of training and equipment can potentially cost several thousand pounds. To justify this level of expenditure, the equipment has to be in very regular use, so some dealers and installers opt instead to use the services of established calibrators.

Specifying good products, then installing them well, has always been the selling point of the custom install industry. It should now include ISF calibration on each and every install and, particularly with projection systems, a regular follow up.

Piers Clerk is the founder of Home Cinema Engineering, provider of video and audio calibration services throughout the UK.

www.homecinemaengineering.com