Coloring Internal Cavities for Virtual Endoscopy

Omer Shibolet (1,2) and Daniel Cohen-Or (1)

(1) School of Mathematical Sciences, Tel-Aviv University, Ramat-Aviv 69978, Israel
(2) Algotec Systems Ltd, 4 Ha-Melacha St., POB 2408, Raanana 43000, Israel


This paper describes a method for coloring voxel-based models. The method generalizes the two-part texture mapping technique to color complex and non-convex objects in a more natural way. The method was developed for coloring internal cavities for the application of virtual endoscopy, where the surfaces are shaped like a twisted general cylinder in the macro-level, but with some folds and bumps in the more detailed levels. Given a flat texture, the coloring method defines a mapping between the 3D surface and the texture which reflects the tensions of the points on the surface. The core of the method is a technique for mapping a non-convex surface to a convex one. The new technique is based on a discrete dilation process that is fast and robust, and bypasses many of the numerical problems common to previous methods.

An updated version of the paper

Coloring Internal Cavities for Virtual Endoscopy(gzipped ps)

An mpeg movie of a Virtual Endoscopy simulation.

click here


The figures below show a sequence of images of a sphere "growing" out of a plan. Using our coloring technique, the texture seems to grow together with the surface as if it a natural process. Note that we do not apply a physical simulation but rather directly color the final shape. The last image shows the same object textured by a naive two-part mapping technique.

The following sequence shows a sample of the dilation process. The original non-convex object slowly transforms into a convex shape. The new voxels are colored in green.

A high resolution image taken during interactive navigation inside a region of the large intestine. This region of the colon is colored using a replicated photograph taken during real colonoscopy (endocopy of the colon).

The replicated texture used to color the above image is

Another view of the colon, taken during virtual endocopy, colored using a different texture.

The following are colon regions colored with replicated images. Notice the preservation of fine details in the process of coloring and rendering.

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