Pre-Processing of Underwater Images Taken in shallow Water for Color Reconstruction Purposes

J. Åhlén, D. Sundgren, and E. Bengtsson (Sweden)


image, underwater, pre-processing, color, correction, light.


Coral reefs are monitored with different techniques in or der to examine their health. Digital cameras, which pro vide an economically defendable tool for marine scientists to collect underwater data, tend to produce bluish images due to severe absorption of light at longer wavelengths. In this paper we study the possibilities of correcting for this color distortion through image processing. The decrease of red light by depth can be predicted by Beer’s Law. An other parameter that has been taken into account is the image enhancement functions built into the camera. We use a spectrometer and a reflectance standard to obtain the data needed to approximate the joint effect of these func tions. This model is used to pre-process the underwater images taken by digital cameras so that the red, green and blue channels show correct values before the images are subjected to correction for the effects of the water column through application of Beer’s Law. This process is fully automatic and the amount of processed images is limited only by the speed of computer system. Experimental re sults show that the proposed method works well for cor recting images taken at different depths with two different cameras.

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