Photographers usually take a shallow focus image to highlight the main subject in the picture and blur the distractions in the background region. Softening these distractions can not only produce special vision effect but also keep the privacy for people in the background. In this work, we develop a brand new defocusing algorithm to simulate the blur effect in the background caused by a wide aperture camera. We also design an easy-to-use interactive interface for user to segment foreground/background objects, adjust the depth of field for images, and assign camera settings. Techniques including lazy snapping, alpha matting, depth information generation and defocusing are integrated in the system. The experimental results show the effectiveness of the proposed methodology.