Natural image matting plays an important role in image and video editing. It has been addressed hotly because it is inherently an under-constrained problem – we must estimate both the foreground and background colors (we call them component colors) at each pixel to calculate its opacity, according to the only known observed color. Prior assumption such as statistics and smoothness are utilized for estimation, but these methods either are simple to handle situations such as complex background and large interaction region or have high computational complexity. This paper proposes a fast technique to estimate the component colors based on structure information. Our approach exploits a simple convolution operation to detect structure information in images. It then uses two kinds of estimation methods to propagate colors based on the structure types. Experimental results show that our method is fast and efficient to handle objects with strong structures and large part of interaction regi...