Fast Hue and Range preserving Histogram Specification. Theory and New Algorithms for Color Image Enhancement
Résumé
Color image enhancement is a complex and challenging task in digital imaging with abundant applications. Preserving the hue (the dominant color ingredient) of the input image is crucial in a wide range of situations. We propose a simple image enhancement methodology where the hue is conserved and the range (the gamut) of the R, G, B channels is optimally preserved. In our setup, the intensity channel of the input image is transformed into an intensity image whose histogram matches a specified, well-behaved target histogram, using the fast strict ordering algorithm [1]. We derive a new color assignment approach that preserves the hue and the range in an optimal way. We analyze our algorithms in terms of their chromaticity improvement and compare them with the unique and quite popular histogram based hue and range preserving algorithm of Naik and Murthy [2]. Numerical tests confirm our theoretical results and show that our algorithms performs much better than the Naik and Murthy algorithm. In spite of its simplicity, it gives quite often better results than the state-of-the art automatic color enhancement algorithm (ACE) [15].
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