Title:	Fast opacity control in rendering of volumetric CT data
Authors:	Csébfalvi, Balázs Szirmay-Kalos, László Márton, Gábor
Citation:	Journal of WSCG. 1997, vol. 5, no. 1-3.
Issue Date:	1997
Publisher:	Václav Skala - UNION Agency
Document type:	článek article
URI:	http://wscg.zcu.cz/wscg1997/wscg97.htm http://hdl.handle.net/11025/15927
ISSN:	1213-6972 (print) 1213-6980 (CD-ROM) 1213-6964 (online)
Keywords:	objemové vykreslování;alpha blending;sledování paprsku;lékařské zobrazování;CT
Keywords in different language:	volume rendering;alpha blending;ray tracing;medical imaging;CT
Abstract in different language:	In 3D rendering of volumetric CT data the alpha-blending technique can be used for modeling semitransparent tissues. This method assigns di erent opacity values to di erent tissue types. In practice, only four materials can be separated according to their CT numbers (Hounsfield density): air, fat, soft tissue and bone. Application of alpha-blending rendering enhances the more important tissues, assigning high opacity value for important tissues and low opacity for less important ones. For each pixel of the image, a ray is traced and the colour of the appropriate pixel is computed as a sum of intersected voxel colours weighted by opacity values. However, this computation is very slow if the size of 3D array is big. Furthermore, if the opacity value of one of the tissues needs to be changed, then the complete time-consuming rendering must be repeated in order to recompute the new weighted sums. In order to allow fast control of opacity values of a new algorithm is presented that provides fast opacity and colour modification after preprocessing the volume with fixed point of view and light source locations.
Rights:	© Václav Skala - UNION Agency
Appears in Collections:	Volume 5, number 1-3 (1997)

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