戶外場景影像中含有大量的資訊，其中在戶外影像是由天空的區域與地面區域的結合，而天際線切開兩個區域；所以若是找出天際線，就可以完美的區分出天空地區的資訊與地面地區的資訊。在天際線的運用上，最開始的研究應用NASA的無人探測車在火星上幫助導航辨識方向旋轉的ㄧ個資訊，後來許多研究開始尋找天際線（天空區域），在一些研究中的應用是透過天際線辨識出場景的位置、可以用來辨識山稜線、影像編輯的前處理，例如：行車紀錄器的路面區域資訊、都市的城市線、風景的輪廓等等。 但因為大多數天際線（天空區域）偵測的研究所使用的場景多半為郊區場景，少數的研究才是以市區為場景，其原因是市區所涵蓋的資訊比郊區複雜更多，例如最先面對的挑戰為建築物大樓與天空相似的問題，或者說有不同形狀的建築物會存在建築內縮的問題（倒三角形），這些都更加深了天際線偵測的困難程度。 本系統資料將包含市區與郊區場景。利用區域切割（Region Segmentation），將影像切割成多組區域再將區域邊界切割成線段，透過機器學習分類（Support Vector Machine）的方式，會取得所有邊界的分類。然後以天際線為天空區域的邊界為前提，使用區域填滿（Region filling）取得天際線。 在機器學習特徵擷取的部分，基於特徵擷取來至區域周圍的邊線上的點，本論文使用色彩資訊（RGB Color Patch）以及紋理資訊（Gray-Level Co-Occurrence Matrix）的兩種特徵混用，再使用主成分分析（Principal component analysis）對特徵後處理；最後本論文所提出的特徵以及分類類別，在分類的實驗最後可以有非常好的結果呈現。 ;The skyline information in an outdoor image scene can provide a lot information such as the horizon and background information for automatic robots. Most existing works find skylines in suburban scenes because the urban scenes are more diverse than suburban scenes. In our paper, we try to find skylines in not only suburban scenes but also urban scenes. We propose a new method to find skylines using region segmentation and boundary feature classification. In the proposed method, we first apply region segmentation methods to obtain region boundaries. Then we use the segmentation result to split the region boundaries to edges. Afterwards, we perform sampling on the segmented region boundaries. Gray-Level Co-Occurrence Matrix (GLCM), color patch descriptors are extracted as the features of sampled pixels on the boundaries. We apply machine learning techniques and use both suburban and urban scenes to perform training. Support vector machine classifiers are used to classify the boundary. The sampled pixels on the boundaries are classified as sky pixel, ground pixel, or skyline pixel. At last, to use the region filling to get the skyline (or sky region). In the experiments, we have tested the performance of the framework using different combinations of region segmentation methods and features. The proposed method exhibits better detection results compared with existing skyline detection methods.
