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Introduction

      Segmentation can only occur where a precise description of structure exists. The language for describing image structure includes: thresholds on a scalar data value range (e.g. x-ray opacity), regions within a vector space of data values (e.g. RGB space), regions within a texture statistics space, gradient edges, transforms for isolating lines and parametric curves, and geometric arrangements of primitive shapes. There is a wide gap between this language and descriptions of anatomically or medically significant features. Humans bring a great deal of expert and contextual knowledge to bear on image recognition problems. When presented with such recognition problems they mentally engage in an iterative visual refinement as they focus on the important features of the image data. This refinement involves a sequence of choices which seek to distinguish significant visual details from irrelevant information. These choices are made in parallel with a visual exploration of the image. This parallel activity is important since the appropriate choices for segmentation are frequently not known until the data has been partially visualized.

     This paper describes the first step of a project to exploit the expert interpretive knowledge of users by providing an interactive, immersive environment in which users directly control the segmentation and visualization process. The Visible Human cryosection data set offers a unique test set in which to examine these ideas.


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