Chul Lee
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Computationally Efficient Brightness-Compensated Contrast Enhancement

Abstract

High quality displays tend to consume significant power in mobile devices. Currently, transmissive liquid crystal displays are among the most common. They are non-emissive and rely on a backlight behind the display panel. Brightness compensation refers to the signal processing technique to adaptively dim the backlight to reduce the power consumption, while increasing the pixel values to preserve the visual quality of the images or even to enhance their contrast. Fast computation of the brightness compensation algorithm is essential for practical use. In this paper, we show that a state-of-the-art brightness compensation algorithm, which requires iterations and is computationally demanding, can in fact be solved with a closed-form solution. We also demonstrate with experimental results that we can achieve approximately an 800-fold speed-up, while providing effectively identical images to those obtained by the original method.

Experimental Results

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Fig. 1. Brightness-compensated contrast enhancement results on the Building, Hats, Window, and Stream images at $b = 0.5$. The input images in (a) are compensated by (b) Tsai et al.'s algorithm [1], (c) the iterative solution [2], (d) the approximate solution [3], and (e) the closed-form solution.

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Fig. 2. Comparison of the transformation functions obtained by different methods on (a) Building, (b) Hats, (c) Window, and (d) Stream.

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Table. 1. Computational complexities and the average computation time for all test images.

Reference

  1. P.-S. Tsai, C.-K. Liang, T.-H. Huang, and H. H. Chen, “Image enhancement for backlight-scaled TFT-LCD displays,” IEEE Trans. Circuits and Systems for Video Technology, vol. 19, no. 4, pp. 574–583, Apr. 2009.

  2. C. Lee, J.-H. Kim, C. Lee, and C.-S. Kim, “Optimized brightness compensation and contrast enhancement for transmissive liquid crystal displays,” IEEE Trans. Circuits and Systems for Video Technology, vol. 24, no. 4, pp. 576-590, Apr. 2014.

  3. C. Lee, J.-H. Kim, C. Lee, and C.-S. Kim, “Power-constrained backlight scaling and contrast enhancement for TFT-LCD displays,” in Proc. IEEE Int'l Conf. Image Process., Sep.–Oct. 2012, pp. 2793–2796.

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