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Abstract
Due to their near‐infrared data channel, digital airborne four‐channel imagers provide a potentially good discrimination between vegetation and human‐made materials, which is very useful in automated mapping. Due to their red, green and blue data channels, they also provide natural colour images, which are very useful in traditional (manual) mapping. In this paper, an algorithm is described which provides an approximation to the spectral capabilities of the four‐channel imagers by using a colour‐infrared aerial photo as input. The algorithm is tailored to urban/suburban surroundings, where the quality of the generated (pseudo) natural colour images are fully acceptable for manual mapping. This brings the combined availability of near‐infrared and (pseudo) natural colours within reach for mapping projects based on traditional photogrammetry, which is valuable since traditional analytical cameras still by far outnumber the relatively new family of digital airborne four‐channel imagers.
Acknowledgements
The author wishes to thank Allan Hanbury of the Pattern Recognition and Image Processing Group, Vienna University of Technology, who developed the ‘Improved HLS’ colour space and provided the code for the transformations.
Additional thanks go to cartographers Anders Nielsen, Jens Bo Rykov and Flemming Hjorth Jensen, of Kort & Matrikelstyrelsen, who inspected the results presented here, ensuring that they were acceptable for cartographic work.
