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Article

Horizon Line Detection in Historical Terrestrial Images in Mountainous Terrain Based on the Region Covariance

Department of Geodesy and Geoinformation, TU Wien, 1040 Vienna, Austria
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Author to whom correspondence should be addressed.
Academic Editor: Bryan Gardiner
Remote Sens. 2021, 13(9), 1705; https://doi.org/10.3390/rs13091705
Received: 24 March 2021 / Revised: 25 April 2021 / Accepted: 26 April 2021 / Published: 28 April 2021
(This article belongs to the Special Issue Classification and Feature Extraction Based on Remote Sensing Imagery)
Horizon line detection is an important prerequisite for numerous tasks including the automatic estimation of the unknown camera parameters for images taken in mountainous terrain. In contrast to modern images, historical photographs contain no color information and have reduced image quality. In particular, missing color information in combination with high alpine terrain, partly covered with snow or glaciers, poses a challenge for automatic horizon detection. Therefore, a robust and accurate approach for horizon line detection in historical monochrome images in mountainous terrain was developed. For the detection of potential horizon pixels, an edge detector is learned based on the region covariance as texture descriptor. In combination with shortest path search the horizon in monochrome images is accurately detected. We evaluated our approach on 250 selected historical monochrome images in average dating back to 1950. In 85% of the images the horizon was detected with an error less than 10 pixels. In order to further evaluate the performance, an additional dataset consisting of modern color images was used. Our method, using only grayscale information, achieves comparable results with methods based on color information. In comparison with other methods using only grayscale information, accuracy of the detected horizons is significantly improved. Furthermore, the influence of color, choice of neighborhood for the shortest path calculation, and patch size for the calculation of the region covariance were investigated. The results show that both the availability of color information and increasing the patch size for the calculation of the region covariance improve the accuracy of the detected horizons. View Full-Text
Keywords: horizon detection; region covariance; historical images; edge detection horizon detection; region covariance; historical images; edge detection
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MDPI and ACS Style

Mikolka-Flöry, S.; Pfeifer, N. Horizon Line Detection in Historical Terrestrial Images in Mountainous Terrain Based on the Region Covariance. Remote Sens. 2021, 13, 1705. https://doi.org/10.3390/rs13091705

AMA Style

Mikolka-Flöry S, Pfeifer N. Horizon Line Detection in Historical Terrestrial Images in Mountainous Terrain Based on the Region Covariance. Remote Sensing. 2021; 13(9):1705. https://doi.org/10.3390/rs13091705

Chicago/Turabian Style

Mikolka-Flöry, Sebastian; Pfeifer, Norbert. 2021. "Horizon Line Detection in Historical Terrestrial Images in Mountainous Terrain Based on the Region Covariance" Remote Sens. 13, no. 9: 1705. https://doi.org/10.3390/rs13091705

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