Journal
OPTIK
Volume 125, Issue 24, Pages 7143-7148Publisher
ELSEVIER GMBH
DOI: 10.1016/j.ijleo.2014.07.118
Keywords
Retinex; Nighttime image; Image enhancement; Sigmoid function
Categories
Funding
- National Natural Science Foundation of China [61273245, 91120301]
- 973 Program [2010CB327904]
- Program for New Century Excellent Talents in University of Ministry of Education of China [NCET-11-0775]
- Beijing Key Laboratory of Digital Media, Beihang University, Beijing, PR China [100191]
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We propose a retinex improvement for nighttime image enhancement. Retinex is often used on images under non-uniform illumination in terms of either color or lightness and has satisfactory results to achieve color constancy and dynamic range compression. Few studies focus retinex on nighttime images, especially those under extreme conditions (i.e., images with over-lighted or extremely under-lighted areas or with noise speckles), on which retinex operation can perform badly. Original multi-scale retinex (MSR) is extremely sensitive to noise speckles that cameras produce in low light areas, and it has unsatisfactory effect on areas with normal or intensive illumination. Moreover, original MSR uses a gain-offset method for prior-to-display treatment and can lead to apparent data loss on nighttime images. This paper replaces the logarithm function in MSR with a customized sigmoid function to minimize data loss, and adapts MSR to nighttime images by merging results from sigmoid-MSR with original images. Experiments show our framework, when applied to nighttime images, can preserve areas with normal or intensive lighting and suppress noise speckles in extreme low light areas. (C) 2014 Elsevier GmbH. All rights reserved.
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