Improving image quality in poor visibility conditions using aphysical model for contrast degradation
Oakley, J.P.; Satherley, B.L.
Image Processing, IEEE Transactions on
Volume 7, Issue 2, Feb 1998 Page(s):167 - 179
Digital Object Identifier 10.1109/83.660994
Summary:In daylight viewing conditions, image contrast is often
significantly degraded by atmospheric aerosols such as haze and fog.
This paper introduces a method for reducing this degradation in
situations in which the scene geometry is known. Contrast is lost
because light is scattered toward the sensor by the aerosol particles
and because the light reflected by the terrain is attenuated by the
aerosol. This degradation is approximately characterized by a simple,
physically based model with three parameters. The method involves two
steps: first, an inverse problem is solved in order to recover the three
model parameters; then, for each pixel, the relative contributions of
scattered and reflected flux are estimated. The estimated scatter
contribution is simply subtracted from the pixel value and the remainder
is scaled to compensate for aerosol attenuation. This paper describes
the image processing algorithm and presents an analysis of the
signal-to-noise ratio (SNR) in the resulting enhanced image. This
analysis shows that the SNR decreases exponentially with range. A
temporal filter structure is proposed to solve this problem. Results are
presented for two image sequences taken from an airborne camera in hazy
conditions and one sequence in clear conditions. A satisfactory
agreement between the model and the experimental data is shown for the
haze conditions. A significant improvement in image quality is
demonstrated when using the contrast enhancement algorithm in conjuction
with a temporal filter
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