computer methods and programs in biomedicine 97 ( 2 0 1 0 ) 99–113 journal homepage: www.intl.elsevierhealth.com/journals/cmpb Accelerating volume rendering by ray leaping with back steps Ömer Cengiz C ¸ elebi * , Ulus C ¸ evik 1 C ¸ ukurova University, Adana, Turkey article info Article history: Received 5 January 2009 Received in revised form 12 April 2009 Accepted 12 May 2009 Keywords: Information visualization Volume visualization Visualization techniques and methodologies Space leaping Ray leaping abstract The methods for visualizing sampled spatial scientific data are known as volume rendering, where images are generated by computing 2D projections of 3D volume data. Since all the discrete data cells participate in the generation of each image, rendering time grows lin- early with the resolution and complexity of the dataset. Empty cells in the data, which do not contribute to the final image, are of the important factors that increase the rendering time. During recent years, researchers have highly concentrated on improving the perfor- mance of these methods to achieve real time rendering. Skipping the empty space provides significant speedup and known as space leaping which requires implementation of special data structures and pre-processing. This paper presents a simple and efficient technique, that we name “ray-leaping,” for the acceleration of total rendering process and eliminates the need for special data structures and pre-processing. © 2009 Elsevier Ireland Ltd. All rights reserved. 1. Introduction Visualization is the usage of computer supported, interactive, visual representations of data to enable understanding while maintaining the integrity and accuracy of the information. Sci- entific visualization is the visualization of physically based data. Volume visualization is the technique of displaying two- dimensional projections of three-dimensional (volume) data. Data may be acquired from various medical scanners. Visual- izing a given three-dimensional dataset can be done using two different approaches: surface rendering, and volume render- ing. Surface rendering algorithms first fit geometric primitives to values in the data, and then render these primitives. Vol- ume rendering algorithms render voxels in the volume dataset directly, without converting to geometric primitives. They ∗ Corresponding author at: Inclipinar Mah. Prof. Muammer Aksoy Blv. 14. Sok. Prestij Apt. A-Blok, No: 5/11, 27090 Sehitkamil, Gaziantep, Turkey. Tel.: +90 532 421 62 77; fax: +90 342 220 48 04. E-mail addresses: cengiz@celebisoftware.com (Ö.C. C ¸ elebi), ucevik@cukurova.edu.tr (U. C ¸ evik). 1 Address: University of C ¸ukurova, Department of Electrical and Electronics Eng., 01330 Adana, Turkey. Tel.: +90 322 338 68 68; fax: +90 322 338 63 26. usually include an illumination model, which supports semi- transparent voxels. Volume rendering can produce informative images that can be useful in data analysis, but a major drawback of the techniques is the time required to generate a high-quality image. An interactive volume visualization scheme requires a performance in the order of Terra (10 12 ) operations per second [1]. General-purpose processors alone cannot provide such a performance, and so, additional solutions have been devel- oped which decrease rendering times, and therefore increase interactivity and productivity. For the optimization of vol- ume visualization there are five main approaches [2]: data reduction by means of model extraction or data simplifica- tion, software-based algorithm optimization and acceleration, implementation on general purpose parallel architectures, 0169-2607/$ – see front matter © 2009 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.cmpb.2009.05.007