Underwater Photogrammetry
Task Group

References








Single Image Haze Removal Using Dark Channel Prior


The Chinese University of Hong Kong
Microsoft Research Asia
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- Video demontration
- Matlab code

Abstract

In this paper, we propose a simple but effective image prior - dark channel prior to remove haze from a single input image. The dark channel prior is a kind of statistics of the haze-free outdoor images. It is based on a key observation - most local patches in haze-free outdoor images contain some pixels which have very low intensities in at least one color channel. Using this prior with the haze imaging model, we can directly estimate the thickness of the haze and recover a high quality haze-free image. Results on a variety of outdoor haze images demonstrate the power of the proposed prior. Moreover, a high quality depth map can also be obtained as a by-product of haze removal.






An Image Based Technique for Enhancement of Underwater Image


Department of P.G. Studies and Research in Computer Science Kuvempu University, Shankaraghatta-577451, Karnataka, India.
Corresponding Author: Email- psajjan@yahoo.com
IJMI
International Journal of Machine Intelligence
ISSN: 0975–2927 & E-ISSN: 0975–9166, Volume 3, Issue 4, 2011, pp-217-224
- Available online
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Abstract

The underwater images usually suffers from non-uniform lighting, low contrast, blur and diminished colors. In this paper, we proposed an image based preprocessing technique to enhance the quality of the underwater images. The proposed technique comprises a combination of four filters such as homomorphic filtering, wavelet denoising, bilateral filter and contrast equalization. These filters are applied sequentially on degraded underwater images. The literature survey reveals that image based preprocessing algorithms uses standard filter techniques with various combinations. For smoothing the image, the image based preprocessing algorithms uses the anisotropic filter. The main drawback of the anisotropic filter is that iterative in nature and computation time is high compared to bilateral filter. In the proposed technique, in addition to other three filters, we employ a bilateral filter for smoothing the image. The experimentation is carried out in two stages. In the first stage, we have conducted various experiments on captured images and estimated optimal parameters for bilateral filter. Similarly, optimal filter bank and optimal wavelet shrinkage function are estimated for wavelet denoising. In the second stage, we conducted the experiments using estimated optimal parameters, optimal filter bank and optimal wavelet shrinkage function for evaluating the proposed technique. We evaluated the technique using quantitative based criteria such as a gradient magnitude histogram and Peak Signal to Noise Ratio (PSNR). Further, the results are qualitatively evaluated based on edge detection results. The proposed technique enhances the quality of the underwater images and can be employed prior to apply computer vision techniques.






Enhancing Underwater Images and Videos by Fusion


Hasselt University - tUL -IBBT, EDM, Belgium
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Abstract

This paper describes a novel strategy to enhance under-water videos and images. Built 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 corrected and contrast enhanced 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 single image approach that does not require specialized hardware or knowledge about the underwater conditions or scene structure. Our fusion framework also supports temporal coherence between adjacent frames by performing an effective edge preserving noise reduction strategy. The enhanced images and videos are characterized by reduced noise level, better exposedness of the dark regions, improved global contrast while the finest details and edges are enhanced significantly. In addition, the utility of our enhancing technique is proved for several challenging applications.






Initial Results in Underwater Single Image Dehazing


Department of Electrical Engineering and Computer Science
Department of Naval Architecture and Marine Engineering
University of Michigan, Ann Arbor, Michigan 48109

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Abstract

As light is transmitted from subject to observer it is absorbed and scattered by the medium it passes through. In mediums with large suspended particles, such as fog or turbid water, the effect of scattering can drastically decrease the quality of images. In this paper we present an algorithm for removing the effects of light scattering, referred to as dehazing, in underwater images. Our key contribution is to propose a simple, yet effective, prior that exploits the strong difference in attenuation between the three image color channels in water to estimate the depth of the scene. We then use this estimate to reduce the spatially varying effect of haze in the image. Our method works with a single image and does not require any specialized hardware or prior knowledge of the scene. As a by-product of the dehazing process, an up-to-scale depth map of the scene is produced. We present results over multiple real underwater images and over a controlled test set where the target distance and true colors are known.






Underwater Image Enhancement: Using Wavelength Compensation and Image Dehazing


Department of Computer Science Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan chiang@cse.nsysu.edu.tw,
Department of Management Information Systems and Institute of Biomedical Engineering and Material Science, Central Taiwan University of Science and Technology, Taichung, Taiwan

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Abstract

Underwater environments often cause color scatter and color cast during photography. Color scatter is caused by haze effects occurring when light reflected from objects is absorbed or scattered multiple times by particles in the water. This in turn lowers the visibility and contrast of the image. Color cast is caused by the varying attenuation of light in different wavelengths, rendering underwater environments bluish. To address distortion from color scatter and color cast, this study proposes an algorithm to restore underwater images that combines a dehazing algorithm with wavelength compensation (WCID). Once the distance between the objects and the camera was estimated using dark channel prior, the haze effects from color scatter were removed by the dehazing algorithm. Next, estimation of the photography scene depth from the residual energy ratios of each wavelength in the background light of the image was performed. According to the amount of attenuation of each wavelength, reverse compensation was conducted to restore the distortion from color cast. An underwater video downloaded from the Youtube website was processed using WCID, Histogram equalization, and a traditional dehazing algorithm. Comparison of the results revealed that WCID simultaneously resolved the issues of color scatter and color cast as well as enhanced image contrast and calibrated color cast, producing high quality underwater images and videos.






A photogrammetric approach to survey floating and semi-submerged objects


3D Optical Metrology unit, Bruno Kessler Foundation (FBK), 38123 Trento, Italy
Parthenope University of Naples, Dept. of Applied Science, 80143 Naples, Italy

- Full paper here

Abstract

The article presents an innovative methodology for the 3D surveying and modeling of floating and semi-submerged objects. Photogrammetry is used for surveying both the underwater and emerged parts of the object and the two surveys are combined together by means of special rigid orientation devices. The proposed methodology is firstly applied to a small pleasure boats (approximately 6 meters long) - hence a free floating case - and then to a large shipwreck (almost 300 meters long) interested by a 52 m long leak at the waterline. The article covers the entire workflow, starting from the camera calibration and data acquisition down to the assessment of the achieved accuracy, the realization of the digital 3D model by means of dense image matching procedures as well as deformation analyses and comparison with the craft original plane.






Photogrammetric Techniques For 3-D Underwater Record Of The Antique Time Ship From Phanagoria


ANO Contemporary Technologies in Archaeology and History, Moscow, Russia (mzhukovsky@mail.ru).
Institute of Archaeology RAS, Moscow, Russia (ptakkon@yandex.ru).

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Abstract

Phanagoria – the largest known ancient Greek settlement on the territory of Russia is situated on the Taman peninsula on the southern side of the Taman bay. The unique feature of the site is that about 1/3 of the settlement of Phanagoria is currently flooded by waters of the Taman bay due to the transgression of the Black sea level since antiquity. In 2012 in the course of underwater prospection of the Taman bay a wooden ship buried under the 1.5 m thick bottom sediments was discovered in situ. The unique feature of the ship is excellent preservation of its wooden parts, which makes it one of the few finds of this kind ever made on the territory of Russia. This paper presents a case-study of application of photogrammetry technique for archaeological field documentation record in course of underwater excavations of the Phanagorian shipwreck. The advantages and possible underwaterspecific constraints of automated point cloud extraction algorithm which was used in the research are discussed. The paper gives an overview of the practical aspects of the workflow of photgrammetry technique application at the excavation ground: photo capture procedure and measurement of control points. Finally a resulting 3-D model of the shipwreck is presented and high potential of automated point cloud extraction algorithms for archaeological documentation record is concluded.