Uniform Out--of-focus blur
-When a camera images a 3D scene onto a 2D imaging plane, some parts of the scene are in focus while other parts are not. If the aperture of the camera is circular, the image of any point source is a small disk, known as the circle of confusion(COC)
-The degree of defocus (diameter of the COC) depends on the focal length and the aperture number of the lens, and the distance between camera and object.