Automatic comic frame extraction is the core technique for comic content adaptation. Typical algorithms segment a comic page into a set of frames using connected components or division lines, but they cannot produce frames without blank margins and there is still room for improvement for complex comic images. We present a method that identifies frame polygons via connected component labeling and line segments combination. We analyze lines within each component and preliminarily judge the frame type, and then we optimize an energy-like score function constrained by several rules to choose frames. Experimental results indicate an increase of both accuracy and F-score compared with previous methods.