Abstract: In order to realize the external shape description for banana， a banana shape description method based on change parameters for double ellipses has been proposed. First of all， the binary image of the object was obtained by image processing. The ellipse curve fitting of the two dimensional point set was provided by the library function cv.fitEllipse in Open Source Computer Vision Library （OPENCV）， and the external outline of ellipse was selected as the initial contour. Then， based on the first step， the external ellipse and inscribed ellipse with variable parameters was constructed， and the banana shape fitting was described based on the areas of double ellipses overlap. Finally， the double ellipses parameters describing the banana shape were extracted as characteristic parameter， which was used to describe the shape for the other types of fruits and vegetables， and to determine the effectiveness of the characteristic parameters. Experimental results showed that the proposed method was simple， fast and efficient. The operation speed was about 0.1 s on the FX6300 AMD processor platform. The algorithm was written in C++ language， which can be used in automatic production line for fruit sorting and packing.

Key words: outline of ellipse, banana shape, parameterized description, fruit classification