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    March 15, 2005
    Projector Calibration
    Dear Gary: As a long-time subscriber to Widescreen Review, I have learned much about the various aspects of home theatre setups. With a library of more than 200 LaserDiscs and close to 600 DVDs in my collection at the moment, it can be said that it is a hobby that consumes my being. Thanks to you guys at WSR, I have also managed to put together a modest but decent collection of projection and audio components into a room of some 320 square feet that really gives me much pleasure constantly. WSR regularly advises in its feature articles and test reports about the importance of a properly calibrated display component with regard to contrast, brightness, color, hue, and sharpness levels. However, the display component is not the only one in the projection chain which has controls on these aspects of the screen image. Video processors, DVD and LaserDisc players also do have them. If one were to optimize the display component, will tinkering with the setups on processor or players undo the settings on the former. For example, will increasing the contrast level on the processor cause the projector CRTs to be overdriven and risk CRT burns? So far, I have never read anything that says that display calibrations should be done in conjunction with the video settings on components preceding the display unit in the chain. Or is it unnecessary at all? I would be rather grateful if you could enlighten me on this. Thanks for your excellent magazine.

    Benjamin Lee, Singapore

    mailto:benleeys@singnet.com.sg

    Video Technical Editor Greg Rogers Comments:

    High quality video displays and processors are designed to perform optimally when they receive standard signal levels. Therefore, video sources and processors should produce standard levels. A DVD player, for example, should produce the standard black level and standard peak white level from its analog or digital video outputs. If a DVD player contrast setting produces signal levels that are too large, the signals may be clipped by the next component in the video signal chain making it impossible to distinguish bright details in the image. If a source produces a signal range that is too small, analog signals must be amplified or digital signal levels must be scaled by another component, which may add noise to the picture. If a source black level is set too low, that source or the next component in the video chain may clip near-black levels. It shouldn't be necessary for sources to provide additional adjustments (contrast, brightness, color saturation and hue) if they produce standard signal levels. When they don’t have standard levels the adjustments provided are often too coarse to accurately correct the errors. An internal (to the display) or external video processor (upconverter or scaler) usually has the necessary adjustments to compensate for the calibration errors of multiple input devices. However, it is useful for sources to provide a choice of analog YPbPr black level (with or without 7.5 IRE setup) and a choice of DVI levels (Video or PC) to match the requirements of different video standards. The video processor is also the best place to make temporary adjustments (color saturation for instance) for user preferences while watching a particular movie or broadcast. Normally the best strategy for calibrating a video chain is to start by calibrating the display device and then work backward. Gray scale calibration, in particular, is dependent on the signal levels at the display device. When a display is connected to an external video processor via a DVI digital connection, it is important that both products are calibrated to use the same DVI levels (preferably DVI-video rather than DVI-PC levels). When an analog RGB connection is used between an external processor and a display, mismatches in calibration between the RGB signal channels will also affect the display's grayscale calibration. Therefore, the display's gray scale calibration should be re-optimized using standard test signals applied to the video processor inputs with the video processor controls set to nominal values. Finally, the processor’s controls should be adjusted to match the output signals from individual sources.

    You can E-mail Widescreen Review @ mailto:editorgary@widescreenreview.com

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