(HTW Dresden, Dresden, Germany)

Keywords: UUV, 3D videogrammetry, image enhancement, automatic color transformation

Images taken under water are often of a monochromatic appearance, due to the physical interaction (absorption and reflection) between particles and light sources. Enhanced images with improved saturation, for which the monochromatic character has been corrected, are more suitable for generating 3D models and for identifying structures and materials by human experts.
In this paper we present an automatic method to identify the mean water color from a set of images. This mean color represents an average gray and is used to describe a new axis in CIELab color space. An extended color variance and a histogram equalization are simultaneously applied to the image. The main advantage of this method is the fully automatic enhancement process. An UUV can operate without providing a color reference scheme. The software presented is written in Java and was integrated into the module JEnhancer.
Beside color correction, defocusing and noise reduction are also useful for improving underwater images. JEnhancer was successfully tested in several documentation campaigns to enhance images with different mean colors like blue, green and red, and was integrated into the videogrammetric software pipeline Archaeo3D to produce 3D models from videos. We will showcase its application in diverse real-world case studies from Veruda/Croatia (blue colored salt water), the Surin Islands/Thailand (blue colored salt water), Zwischenahner Meer/Germany (red colored freshwater), Kamenz/Germany (green colored freshwater) and Mondsee/Austria (beige colored freshwater).
JEnhancer is freely available for non-commercial purposes from our project page www.archaeonautic.de.

Relevance conference | Relevance session:
New free methods and low-cost solutions to document underwater archaeology sites are necessary to open up this research area for more archaeological institutes and people.

Fully automatic solution for color correction of underwater images and videos, to be used as the first processing step in an underwater videogrammetry pipeline.