Patent Document ID: 9311561
Application ID: 14425974
Patent Status: 1

Claim One:
1. A histogram equalization apparatus using histogram compression, comprising: a histogram calculation processor calculating a histogram P(X k ) of an input image; a variance calculation processor calculating a histogram variance σ 2 P of the input image or a brightness value variance σ 2 X of the input image, by using the histogram P(X k ) calculated by the histogram calculation processor; a parameter determination processor determining a histogram compression ratio parameter λ according to the histogram variance σ 2 P or the brightness value variance σ 2 X of the input image calculated by the variance calculation processor; a histogram transformation processor compressing the histogram P(X k ) according to the histogram compression ratio parameter λ determined by the parameter determination processor, obtaining a compressed histogram P c (X k ), obtaining a modified histogram P m (X k ), and calculating a cumulative distribution function C m (X k ) of the modified histogram; and a histogram equalization processor performing a histogram equalization by obtaining a modified histogram equalization map, wherein the brightness value variance, σ 2 ⁢ x = ∑ i = 0 K - 1 ⁢ ( X i ⁢ m ) 2 · P ⁡ ( X i ) here, m = ∑ i = 0 K - 1 ⁢ X i · P ⁡ ( X i ) , i represents an integer, K represents a number of expressible brightness value, and X i represents a brightness of an i-th input pixel, and wherein the histogram variance, σ 2 ⁢ p = 1 K ⁢ ∑ i = 0 K - 1 ⁢ ( P ⁡ ( X i ) - T ) 2 , here, T represents an average frequency of the histogram of the input image.