1. A method of processing medical image data with a processor to generate an image to a display for smooth rendering from a defined point of view of one or more vessels with a nearby surrounding area from 3D image data, wherein the one or more vessels are separated from the nearby surrounding area as a centerline tree from the defined point of view, comprising: creating a tubular mesh around the centerline tree; creating an image by rendering the tubular mesh from the defined point of view and saving a depth information of the rendered tubular mesh, wherein corresponding near-plane depth information of the rendered tubular mesh will be saved as a first Z-buffer with non-visible pixels set to value 1; extracting a boundary between the rendered tubular mesh and the nearby surrounding area using the depth information of the rendered tubular mesh; rendering the nearby surrounding area from the defined point of view, including the steps of: extracting from the Z-buffer the pixels that lie on a boundary between visible and non-visible area; storing each boundary pixel's image coordinates as an element in a 2D array; adding four points to the 2D array to define a visualization frustum; creating a 2D mesh as defined by the 2D array elements; and projecting the 2D mesh to a 3D mesh by assigning to each point defining the 2D mesh its corresponding 3D coordinate; combining the renderings of the tubular mesh and the nearby surrounding area; and the processor generating an image to the display, including a first part of the one or more vessels that in the defined point of view lies behind a second part of the one or more vessels and would be obscured by a surrounding area of the second part of the one or more vessels.