Functionality assessment of algorithms for the coloring of images in terms of increasing radiometric values of aerial photographs archives

Available on the commercial market are a number of algorithms that enable assigning to pixels of a monochrome digital image suitable colors according to a strictly defined schedule. These algorithms have been recently used by professional film studios involved in the coloring of archival productions. This article provides an overview on the functionality of coloring algorithms in terms of their use to improve the interpretation quality of historical, black-and-white aerial photographs. The analysis covered intuitive (Recolored) programs, as well as more advanced (Adobe After Effect, DaVinci Resolve) programs. The use of their full functionality was limited by the too large information capacity of aerial photograph images. Black-and-white historical aerial photographs, which interpretation quality in many cases does not meet the criteria posed on photogrammetric developments, require an increase of their readability. The solution in this regard may be the process of coloring images. The authors of this article conducted studies aimed to determine to what extent the tested coloring algorithms enable an automatic detection of land cover elements on historical aerial photographs and provide color close to the natural. Used in the studies were archival black-and-white aerial photographs of the western part of Warsaw district made available by the Main Centre of Geodetic and Cartographic Documentation, the selection of which was associated with the presence in this area of various elements of land cover, such as water, forests, crops, exposed soils and also anthropogenic objects. In the analysis of different algorithms are included: format and size of the image, degree of automation of the process, degree of compliance of the result and processing time. The accuracy of the coloring process was different for each class of objects mapped on the photograph. The main limitation of the coloring process created shadows of anthropogenic objects, where grey degree values were corresponding to forests.