Abstract
The limited transmittance of LCD panels can be observed as a waste of energy, leading to a limited brightness. Light leaking through LCD panels driven to black, can be observed as a poor black-level, limiting the contrast ratio.
Adaptive Dimming Backlight technology can be applied to attenuate the backlight luminance, improving local contrast, black-level and saving power.
The optical crosstalk between the controllable backlight segments has a negative impact on the dimming performance, limiting the spatial backlight luminance modulation. Crosstalk Compensation can partly compensate this artifact, enhancing the spatial modulation of the segments.
Adaptive Boosting Backlight technology can be applied to boost the output of the panel over 100%. This improves the local brightness and contrast for a sparkling picture, still saving power.
Crosstalk compensation enables deeper dimming. Deeper dimming improves on contrast and enables more boosting for an even brighter picture. So when these technologies are combined:
- the contrast may increase up to 5 times (CCFL/EEFL)
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- the brightness may double and contrast may increase up to 20 times (HCFL).
- Alternatively, for 2D-Dimming the spatial contrast may increase up to a factor of 100 and the temporal contrast may increase to infinite (LED). At the same time, up to 50% average power can be saved!
1. Introduction
LCD-TV systems need to render video and multi-media images with an optimal front-of-screen performance. They have to meet many requirements, like: contrast, brightness, color, flicker, motion portrayal, viewing angle, dissipation and cost.
All these items are directly related to the backlight.
LCD-TV's require a high brightness hence these systems typically use direct-lit LCD panels.
The dimming/boosting properties of the existing light sources are listed in next table. The max power range in the table shows the headroom for boosting of the light sources in typical applications. If more light sources are installed, this number increases proportionally. Hence installing more light sources enables more boosting and better X-talk compensation saving more power with better performances.
At the SID2006 exhibition our 1D-Dimming and Boosting backlight concept was shown at the Philips Booth and got a lot of positive feedback. The main benefits are:
- Spatial contrast and brightness enhancement
- Black-level improvement.
- More local dimming and boosting.
- Continuous power reduction
Table 1: normalized power range
In this paper we will show the benefits of this technology, and extend the scope to 2D backlights. In a 2D-mode (possibly per R, G and B channel), the spatial dimming and boosting technologies have an even higher impact on contrast improvement and power reduction.
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