Histogram equalization: Difference between revisions

Revision as of 18:48, 3 July 2024

Revision as of 03:47, 31 July 2024

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== Of color images ==

The above describes histogram equalization on a grayscale image. However it can also be used on color images by applying the same method separately to the Red, Green and Blue components of the [[RGB]] color values of the image. However, applying the same method on the Red, Green, and Blue components of an RGB image may yield dramatic changes in the image's [[color balance]] since the relative distributions of the color channels change as a result of applying the algorithm. However, if the image is first converted to another color space, [[Lab color space]], or [[HSL and HSV|HSL/HSV color space]] in particular, then the algorithm can be applied to the [[luminance]] or value channel without resulting in changes to the hue and saturation of the image.<ref>S. Naik and C. Murthy, "[httphttps://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=1257395 Hue-preserving color image enhancement without gamut problem]," IEEE Trans. Image Processing, vol. 12, no. 12, pp. 1591–1598, Dec. 2003</ref>

There are several histogram equalization methods in 3D space. Trahanias and Venetsanopoulos applied histogram equalization in 3D color space<ref>P. E. Trahanias and A. N. Venetsanopoulos, "[httphttps://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=202045 Color image enhancement through 3-D histogram equalization]," in Proc. 15th IAPR Int. Conf. Pattern Recognition, vol. 1, pp. 545–548, Aug.-Sep. 1992.</ref> However, it results in "whitening" where the probability of bright pixels are higher than that of dark ones.<ref>N. Bassiou and C. Kotropoulos, "[http://www.sciencedirect.com/science/article/pii/S1077314206002141 Color image histogram equalization by absolute discounting back-off]," Computer Vision and Image Understanding, vol. 107, no. 1-2, pp.108-122, Jul.-Aug. 2007</ref> Han et al. proposed to use a new cdf defined by the iso-luminance plane, which results in uniform gray distribution.<ref>{{Cite journal|doi = 10.1109/TIP.2010.2068555|title = A Novel 3-D Color Histogram Equalization Method with Uniform 1-D Gray Scale Histogram|year = 2011|last1 = Han|first1 = Ji-Hee|last2 = Yang|first2 = Sejung|last3 = Lee|first3 = Byung-Uk|journal = IEEE Transactions on Image Processing|volume = 20|issue = 2|pages = 506–512|pmid = 20801744| bibcode=2011ITIP...20..506H |s2cid = 17972519}}</ref>

==Examples==