Display Data Processing


We use methods from Discrete Optimization to improve modern flat panel displays (e.g. AMLCD, Plasma, OLED devices). Our objective is to reduce power consumption and degradation effects.
For Plasma and OLED displays, we model the addressing of the pixels as combinatorial matrix decomposition problems, which can be represented straight forward with integer linear programming. Depending on the physical addressing mechanism, we refine these models to exploit their combinatorial (sub)structure, e.g., network flows, matchings, or graph coloring problems. From the theoretical perspective, we investigate under which conditions these problems become polynomial-time solvable. However, the algorithms have to compute the decompositions in real-time for being relevant in practice. Hence, we derive fully combinatorial approximation algorithms, which are well suited for being implemented on a chip driving such a display.

The pixels of active matrix liquid chrystal displays (AMLCD) do not emit light but they filter the light coming from the back to shine with the appropriate brightness. In modern displays, multiple light emitting diodes (LED) more and more replace single cold cathode fluorescent lamps (CCFL). This offers a possibility to enhance the visual quality (e.g. contrast ratio) and to save energy by so-called local dimming. That is, the brightness of the backlights are adapted (individually or in groups) to the nearby image content. We use a linear programming model to compute the waveforms of the electrical currents for the LEDs such that each pixel always receives enough light to avoid clipping effects.

Selected Publications

F. Eisenbrand, A. Karrenbauer, M. Skutella, C. Xu, “Multiline Addressing by Network Flow“, Algorithmica, vol. 53, no. 4, pp. 583-596, 2009
(a preliminary version appeared in the Proceedings of the
14th Annual European Symposium on Algorithms (ESA), 2006, pp. 744-755)
A. Karrenbauer, “Matching techniques ride to rescue OLED displays“, Proceedings of the 3rd Annual International Conference on Combinatorial Optimization and Applications (COCOA), 2009, LNCS 5573, pp. 110-122
M. Albrecht, A. Karrenbauer, C. Xu, “A Video-Capable Algorithm for Local-Dimming RGB Backlight“, SID 2009 International Symposium Digest of Technical Papers, 2009, pp. 753-756
M. Albrecht, A. Karrenbauer, C. Xu, “A clipper-free Algorithm for efficient HW-Implementation of local dimming LED-Backlight“, Proceedings of the 28th International Display Research Conference (IDRC), 2008, pp. 286-289
C. Xu, A. Karrenbauer, K. M. Soh, C. Codrea, “Consecutive multiline addressing: A scheme for addressing PMOLEDs”, Journal of the Society for Information Display, vol. 16, no. 2, pp. 211–219, 2008
F. Eisenbrand, A. Karrenbauer, C. Xu, “Algorithms for longer OLED Lifetime“, Proceedings of the 6th International Workshop on Experimental Algorithms (WEA),  LNCS 4525, Springer, 2007, pp. 338-351
C. Xu, A. Karrenbauer, K. M. Soh, J. Wahl, “A new addressing scheme for PM OLED Display”, SID 2007 International Symposium Digest of Technical Papers, 2007, pp. 97-100