Shape-enhanced maximum intensity projection

Abstract

Maximum intensity projection (MIP) displays the voxel with the maximum intensity along the viewing ray, and this offers simplicity in usage, as it does not require a complex transfer function, the specification of which is a highly challenging and time-consuming process in direct volume rendering (DVR). However, MIP also has its inherent limitation, the loss of spatial context and shape information. This paper proposes a novel technique, shape-enhanced maximum intensity projection (SEMIP), to resolve this limitation. Inspired by lighting in DVR to emphasize surface structures, SEMIP searches a valid gradient for the maximum intensity of each viewing ray, and applies gradient-based shading to improve shape and depth perception of structures. As SEMIP may result in the pixel values over the maximum intensity of the display device, a tone reduction technique is introduced to compress the intensity range of the rendered image while preserving the original local contrast. In addition, depth-based color cues are employed to enhance the visual perception of internal structures, and a focus and context interaction is used to highlight structures of interest. We demonstrate the effectiveness of the proposed SEMIP with several volume data sets, especially from the medical field.