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Åhlén, Julia
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Publications (3 of 3) Show all publications
Åhlén, J., Sundgren, D., Lindell, T. & Bengtsson, E. (2005). Dissolved Organic Matters Impact on Colour. In: Image Analysis: 14th Scandinavian Conference, SCIA 2005 (pp. 1148-1156).
Open this publication in new window or tab >>Dissolved Organic Matters Impact on Colour
2005 (English)In: Image Analysis: 14th Scandinavian Conference, SCIA 2005, 2005, p. 1148-1156Conference paper, Published paper (Refereed)
Abstract [en]

The natural properties of water column usually affect under-water

imagery by suppressing high-energy light. In application such as

color correction of underwater images estimation of water column parameters is crucial. Diffuse attenuation coefficients are estimated and used for further processing of underwater taken data. The coefficients will give information on how fast light of different wavelengths decreases with increasing depth. Based on the exact depth measurements and data from a spectrometer the calculation of downwelling irradiance will be done. Chlorophyll concentration and a yellow substance factor contribute to a great variety of values of attenuation coefficients at different depth. By taking advantage of variations in depth, a method is presented to

estimate the in uence of dissolved organic matters and chlorophyll on color correction. Attenuation coefficients that depends on concentration of dissolved organic matters in water gives an indication on how well any spectral band is suited for color correction algorithm.

National Category
Computer Vision and Robotics (Autonomous Systems)
Identifiers
urn:nbn:se:uu:diva-76159 (URN)3-540-26320-9 (ISBN)
Available from: 2006-02-27 Created: 2006-02-27 Last updated: 2018-01-14
Åhlén, J., Sundgren, D. & Bengtsson, E. (2005). Pre-Processing of Underwater Images Taken in shallow Water for Color Reconstruction Purposes. In: IASTED Proceeding (479): IASTED 7th Conference on Signal and Image Processing - 2005.
Open this publication in new window or tab >>Pre-Processing of Underwater Images Taken in shallow Water for Color Reconstruction Purposes
2005 (English)In: IASTED Proceeding (479): IASTED 7th Conference on Signal and Image Processing - 2005, 2005Conference paper, Published paper (Refereed)
Abstract [en]

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.

National Category
Computer Vision and Robotics (Autonomous Systems)
Identifiers
urn:nbn:se:uu:diva-76165 (URN)0-88986-516-7 (ISBN)
Available from: 2006-02-27 Created: 2006-02-27 Last updated: 2018-01-14
Åhlen, J. (2003). Color correction of underwater images based on estimation of diffuse attenuation coefficients. In: Proceedings of 3rd conference for the promotion of research in IT.
Open this publication in new window or tab >>Color correction of underwater images based on estimation of diffuse attenuation coefficients
2003 (English)In: Proceedings of 3rd conference for the promotion of research in IT, 2003Conference paper, Published paper (Other scientific)
National Category
Computer Vision and Robotics (Autonomous Systems)
Identifiers
urn:nbn:se:uu:diva-46278 (URN)
Available from: 2005-08-26 Created: 2005-08-26 Last updated: 2018-01-11
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