Improving retrieval performance of Zernike moment descriptor on affined shapes

Shape (object) description consists a key part of image content description in MPEG-7. In the development of MPEG-7, Zernike moment descriptor (ZMD) has been adopted as region-based shape descriptor. However, because Zernike moments are defined in a unit disk and extracted from shape in polar space, less shape information is used for skewed and stretched shapes. As a result, the extracted ZMD is not robust to skew and stretching distortions. In this paper, an enhanced Zernike moment descriptor (EZMD) is proposed to overcome this drawback. The EZMD is acquired by deriving ZMD from the rotation and scale normalized shape. The rotation and scale normalization effectively suppress the uneven shape distribution within the unit disk and compensates the skew and stretching. Consequently, more shape information is used in the feature extraction. Experimental results show that the proposed EZMD outperforms ZMD significantly.