ε‐separating nonlinear filter bank and its application to face image beautification

Abstract For the purposes of separating the specific components of nonsteady signals, the ε‐separating nonlinear filter bank is proposed. Previously, the authors proposed a nonlinear digital filter called the ε‐filter. This filter effectively eliminates the small signal amplitude random noise superimposed on a signal with a large signal changing component. The ε‐filter bank proposed in this paper consists of these ε‐filters and separates the components by taking account of both the signal amplitude and frequency. Further, a filter system for beautifying facial images using this filter bank is proposed. The human facial image consists not only of large‐signal components such as the frame, eyes, nose, and mouth, but also of small‐signal high‐frequency components such as fine wrinkles as well as small‐signal medium‐frequency components such as large wrinkles and blemishes. Additionally, ultrasmall‐amplitude high‐frequency components expressing the natural roughness of the skin also exist. The present filter bank can eliminate wrinkles and blemishes while maintaining the natural roughness of the skin, allowing beautification of the skin of facial images to be performed effectively. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(4): 52– 62, 2007; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/ecjc.20241