Improved blue sky detection using polynomial model fit

Blue sky commonly appears in photographs. Reliable detection of blue sky can aid semantic image retrieval, image understanding and image enhancement. A novel algorithm is proposed based on a two-dimensional polynomial model of the image of blue sky. An initial sky detection is used to establish high-confidence blue sky regions. Candidate sky regions are found and a two-dimensional polynomial model is used to compute the belief that a given region is also sky. On a database of 83 images, the algorithm correctly classified 31 additional regions as blue sky while adding 8 minor false positives, most of them reflections of sky. Further, the algorithm correctly increased the belief values on 6 regions found by the initial sky detector.