Enhancing Underwater Images and Videos by Fusion
Cosmin Ancuti, Codruta Orniana Ancuti, Tom Haber and Philippe Bekaert
Hasselt University - tUL -IBBT, EDM, Belgium
Abstract
This paper describes a novel strategy to enhance under-
water videos and images. B uilt on the fusion principles, our
strategy derives the inputs and the weight measures only
from the degraded version of the image. In order to over-
come the limitations of the underwater medium we define
two inputs that represent color correc te d and contrast en-
hanced versions of the original underwater image/frame,
but also four weight maps that aim to increase the visibility
of the distant objects degraded due to the medium scattering
and absorption. Our strategy is a sin gle image approach
that does not require specialized hardware or knowledge
about the underwater conditions or scene structure. Our fu-
sion framework also supports temporal coherence between
adjacent frames by performing an effective edge preserving
noise red uction strategy. Th e enhanced images and videos
are characterized by reduced noise level, better exposed-
ness of th e dark regions, improved global contrast while th e
finest details and edges a re enhanced significantly. In ad-
dition, the utility of ou r enhancing technique is proved for
several challenging applica tions.
1. Introduction
Underwater imaging is challeng ing due to the physical
properties existing in such environments. Different from
common images, underwater images suffer from poor vis-
ibility due to the attenuation of the pro pagated light. The
light is attenuated exponentially with the distance and depth
mainly due to absorption and scattering effects. The absorp-
tion substantially reduces the light energy while the scat-
tering causes changes in the light dire ction. The random
attenuation of the light is the main cause of the foggy ap-
pearance while the the fraction of the light scattered back
from the medium along the sight considerably degrades the
scene contrast. The se properties of the underwater medium
yields scenes c haracterized by poor contrast where distant
objects appear misty. Practically, in common sea water, the
objects at a distance of more than 10 meters are almost in-
distinguishab le while the colors are faded since their char-
acteristic wavelengths are cut accordin g to the water depth.
There have been several attempts to restore and enhance
the visibility of such degraded images. Mainly, the prob-
lem can be tackled by using multiple images [21], spe-
cialized hardware [15] and by exploiting polarization fil-
ters [25]. Despite their effectiveness to restore underwater
images, these strategies have demonstrated several impor-
tant issues that reduce their practical applicability. First, the
hardware solutions (e.g. laser range -gated technology and
synchro nous scanning) are relatively expensive and com-
plex. The multiple-imag e solutions requir e several images
of th e same scene taken in different environment conditions.
Similarly, polarization methods process several images that
have different degrees of polarization. While this is rela-
tively feasib le for outdoo r ha zy an d fog gy images, for the
underwater case, the setup of the camera might be trouble-
some. In addition, these methods (except the hardware so-
lutions) are not able to deal with dyn amic scenes, thus being
impractical for videos.
In this paper, we introduce a novel approach that is able
to enhance underwater images based on a single image, as
well as videos of dynamic scenes. Our approach is built on
the fusion principle that has shown utility in several appli-
cations such as image compositing [14], multispectral video
enhance ment [6], defogging [2] and HDR ima ging [20].
In contrast to these methods, our fusion-ba sed approach
does not require multiple images, deriving the inputs and
the weights only from the original degraded image. We
aim for a straightforward a nd computationally inexpen sive
that is able to perform relatively fast on common hardware.
Since the degradation process of underwater scenes is
both multiplicative and additive [26] traditio nal enhancing
techniqu es like white balance, color correction, histogram
equalization shown strong limitations for such a task.
Instead of directly filtering the input image, we developed
a fusion-ba sed scheme driven by the intrinsic properties
of the original image (these properties are represented by
the w eight maps). The success of the fusion techniques
is highly dependent on the choice of the inputs and the
weights and therefore we investigate a set of operators
in order to overco me limitations specific to underwater
environments. As a result, in our framework the degraded
image is firstly white balanced in order to r emove the color
978-1-4673-1228-8/12/$31.00 ©2012 IEEE 81
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