VisionClear Anti-reflection coating

The aim of incorporating anti-reflection technology to the range of BeoVision models currently available is to provide high-quality visual experiences, irrespective of lighting conditions.

Direct reflections caused by lamps and windows are eliminated and the reflection of diffuse light is reduced to a minimum. The result is an improved overall contrast, providing a picture rendition of very high quality even during daylight hours.

Destructive interference

	The coating process consists of applying three layers of a solvent-mixture to a large glass panel. Each layer must be applied with an depth accuracy of 3 - 4%, equalling a measure of just 3 - 4 nanometres (3 - 411000 millimetres). To remove the reflection of a specific colour, a layer at the thickness of exactly 25% of the wavelength needs to be applied. The reflection is then in anti-phase; it is said to 'overlap'.
Reflections from lamps and windows are drastically reduced by the anti-reflection coating. Also the diffuse light emission of lit-up surfaces such as walls, carpets and floors are reduced, providing a high contrast picture. Anti-reflection coating is therefore especially beneficial also for watching TV during daylight hours.
A normal un-coated glass surface reflects about 5% of ambient light, sufficient for detailed mirroring of lit-up objects and surfaces	Applying anti-reflection coating reduces the amount of reflections by a factor of 10, equalling a total reflection of just over 0,5%. The benefit is a clear picture with improved contrast	A triple layer coating is used to widen the range of wavelengths removed, so that the colours most visible to the human eye are eliminated. The only colour which remains as visible reflection is a vague violet tinge.

Eliminating wavelengths

	Graph showing the effect of the three-layer coating to different colours/ wavelengths. The layers are designed to match the colours most sensitive to the human eye. The majority of visible colours are reduced to a reflection below 5%.
The amount of light reflected by the coated surface is reduced to 0,6%, compared to the 5,2% for an uncoated glass surface. Reducing reflections by a factor of 10 drastically reduce the annoyance caused by reflected lamps and windows. However, the most important effect is the improved contrast, as the light from the picture tube does not have to compete with the ambient light in the room. The anti-reflection coating combined with the contrast screen is especially beneficial when television is viewed by daylight or in illuminated surroundings. By applying the greyed contrast screen, the light transmitted by the picture tube is reduced by 50%. However, as diffuse light from the surroundings passes through the contrast screen twice, only 25% of the light is reflected. The result is a significantly increased contrast, adding to the effect of the anti-reflection coating.
	< Characteristic links of the video chain

Note, that after cleaning an antireflection coated surface, all traces of cleansing agent must be removed entirely, as they in principle would influence the thickness of the coating layers, causing the coating to loose its effect.

Development of VisionClear Processing

The picture quality elements of VisionClear are as follows:

• Automatic picture control is the technology that adopts picture on the screen to give the same optimal viewing under any lighting condition in the room. Ambient light is measured and processed to adjust contrast, colour, luminance, sharpness and white point for constant perceived picture quality
• Adaptive luminance-peaking is the processing of the incoming signal to recreate sharpness and detail which was lost by bandwidth limitations of the transmission system. Bang & Olufsen emphasised not to make artificial over-peaked pictures, but natural pictures close to the original. Therefore bandwidth limited signals are peaked, while signals that were already peaked earlier in the chain are not peaked. Likewise the signals from the video tape recorder is less peaked, because this amplifies noise
• Adaptive scan velocity modulation enhances sharpness of horizontal transitions. It is based on processing of RGB and ambient light, adapting this feature to any signal and lighting condition
• The Broadband CTI circuit improves horizontal colour transients enhancing the perceived sharpness also of colours, which are bandwidth-limited in the PAL/ SECAM and VHS systems
• Adaptive black stretch enhances detail of dark parts of the picture, by adding contrast and colour level depending on white level
• Dynamic white balance adjustment enhances detail in light parts of the picture by making these parts more bluish. The two latter elements are both base-d on physical laws of our sight.

The above are the electrical elements of VisionClear. The last and very important elements are mechanical: the contrast glass and the coatings, improving daylight viewing even further (see further details on Contrast Screen Coatings)

Over the years, Bang & Olufsen has improved on these analogue picture improvement technologies to an advanced level in order to deliver the unsurpassed picture quality of their TV sets of today. Furthermore the technologies are the platform for future picture quality, influenced by digital technologies, and will not be made obsolete by this.

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