  A well-known issue of local (adaptive) histogram equalization (LHE) is
over-enhancement (i.e., generation of spurious details) in homogenous areas of
the image. In this paper, we show that the LHE problem has many solutions due
to the ambiguity in ranking pixels with the same intensity. The LHE solution
space can be searched for the images having the maximum PSNR or structural
similarity (SSIM) with the input image. As compared to the results of the prior
art, these solutions are more similar to the input image while offering the
same local contrast.
  Index Terms: histogram modification or specification, contrast enhancement
