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24 April 2008 Fast and robust wavelet-based dynamic range compression with local contrast enhancement
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In this paper, a new wavelet-based dynamic range compression algorithm is proposed to improve the visual quality of digital images captured in the high dynamic range scenes with non-uniform lighting conditions. Wavelet transform is used especially for dimension reduction such that a dynamic range compression with local contrast enhancement algorithm is applied only to the approximation coefficients which are obtained by low-pass filtering and down-sampling the original intensity image. The normalized approximation coefficients are transformed using a hyperbolic sine curve and the contrast enhancement is realized by tuning the magnitude of the each coefficient with respect to surrounding coefficients. The transformed coefficients are then de-normalized to their original range. The detail coefficients are also modified to prevent the edge deformation. The inverse wavelet transform is carried out resulting in a low dynamic range and contrast enhanced intensity image. A color restoration process based on relationship between spectral bands and the luminance of the original image is applied to convert the enhanced intensity image back to a color image.
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Numan Unaldi, Vijayan K. Asari, and Zia-ur Rahman "Fast and robust wavelet-based dynamic range compression with local contrast enhancement", Proc. SPIE 6978, Visual Information Processing XVII, 697805 (24 April 2008);

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