08-12-2012, 02:25 PM
Power-Constrained Contrast Enhancement for Emissive Displays Based on Histogram Equalization
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Abstract
A power-constrained contrast-enhancement algorithm
for emissive displays based on histogram equalization (HE)
is proposed in this paper. We first propose a log-based histogram
modification scheme to reduce overstretching artifacts of the conventional
HE technique. Then, we develop a power-consumption
model for emissive displays and formulate an objective function
that consists of the histogram-equalizing term and the power
term. By minimizing the objective function based on the convex
optimization theory, the proposed algorithm achieves contrast
enhancement and power saving simultaneously. Moreover, we
extend the proposed algorithm to enhance video sequences, as well
as still images. Simulation results demonstrate that the proposed
algorithm can reduce power consumption significantly while
improving image contrast and perceptual quality.
INTRODUCTION
THE RAPID development of imaging technology has
made it easier to take and process digital photographs.
However, we often acquire low-quality photographs since
lighting conditions and imaging systems are not ideal. Much
effort has been made to enhance images by improving several
factors, such as sharpness, noise level, color accuracy, and
contrast. Among them, high contrast is an important quality
factor for providing better experience of image perception to
viewers. Various contrast-enhancement techniques have been
developed. For example, histogram equalization (HE) is widely
used to enhance low-contrast images [1].
HE TECHNIQUES
Many contrast-enhancement techniques have been developed.
HE is one of the most widely adopted approaches to
enhance low-contrast images, which makes the histogram of
light intensities of pixels within an image as uniform as possible
[1]. It can increase the dynamic range of an image by deriving a
transformation function adaptively. A variety of HE techniques
have been proposed [10]–[17]. The main objective of this
paper is to develop a power-constrained image enhancement
framework, rather than to propose a sophisticated contrast-enhancement
scheme. Thus, the proposed PCCE algorithm adopts
the HE approach for its simplicity and effectiveness. Here, we
first review conventional HE and HM techniques and then develop
an LHM scheme, on which the proposed PCCE algorithm
is based.
CONCLUSION
We have proposed the PCCE algorithm for emissive displays,
which can enhance image contrast and reduce power
consumption. We have made a power-consumption model and
have formulated an objective function, which consists of the
histogram-equalizing term and the power term. Specifically,
we have stated the power-constrained image enhancement as
a convex optimization problem and have derived an efficient
algorithm to find the optimal transformation function. Simulation
results have demonstrated that the proposed algorithm
can reduce power consumption significantly while yielding
satisfactory image quality. In this paper,we have employed the
simple LHM scheme, which uses the same transformation function
for all pixels in an image, for the purpose of the contrast
enhancement. One of the future research issues is to generalize
the power-constrained image enhancement framework
to accommodate more sophisticated contrast-enhancement
techniques, such as [10] and [11], which process an input image
adaptively based on local characteristics.