US 9,311,561 B2Granted

Histogram equalization apparatus using histogram compression

AssigneeIndustry Foundation of Chonnam National University

InventorsSung Hoon Hong, Jong In Kim, Jae Won Lee

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Abstract

The present invention relates to a histogram equalization apparatus using histogram compression, and the objective of the present invention is to provide an equalization apparatus which highly compresses a histogram of an input image having a brightness level with a high frequency and lowly compresses the histogram having a brightness level with relatively a lower frequency thereby maintaining the characteristics of the input image, while refraining excessive changes in brightness, and enhancing the contrast more effectively by controlling the strength of a compression ratio according to the characteristics of the input image. To this end, the present invention comprises: a histogram calculation unit for calculating the histogram of the input image; a parameter determination module for determining a histogram compression ratio parameter (λ) according to a brightness value of the input image or the characteristics of the histogram; a histogram transformation unit for compressing the input histogram according to the histogram compression ration parameter (λ) determined by the parameter determination module so as to obtain a compressed histogram, obtaining a modified histogram, and calculating a cumulative distribution function of the modified histogram; and a histogram equalization unit for performing a histogram equalization by obtaining a modified histogram equalization map.

Claims7

Dependent claims

A histogram equalization apparatus using histogram compression, comprising:

a histogram calculation processor calculating a histogram P(Xk) of an input image;
a variance calculation processor calculating a histogram variance σ2P of the input image or a brightness value variance σ2X of the input image, by using the histogram P(Xk) calculated by the histogram calculation processor;
a parameter determination processor determining a histogram compression ratio parameter λ according to the histogram variance σ2P or the brightness value variance σ2X of the input image calculated by the variance calculation processor;
a histogram transformation processor compressing the histogram P(Xk) according to the histogram compression ratio parameter λ determined by the parameter determination processor, obtaining a compressed histogram Pc(Xk), obtaining a modified histogram Pm(Xk), and calculating a cumulative distribution function Cm(Xk) 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 Xi 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.

83 more elements

Dependencies are inferred from the claim text.

Facts

Application: 14/425,974Filed 1 Oct 2013
Priority: KR 10-2013-007524928 Jun 2013
Published: US 2015/0294180 A115 Oct 2015
Granted: 12 Apr 2016
Term ends: Not estimatedThe source records don’t support an estimate.

Classification5 codes

G06T 5/92
Dynamic range modification of images or parts thereof: based on global image properties
G06T 5/40
Image enhancement or restoration: using histogram techniques
H04N 23/81
Camera processing pipelines; Components thereof: for suppressing or minimising disturbance in the image signal generation
G06T
Image data processing or generation, in general