By Charles Rojo

"Glass" is a volume and image manipulation program I've written for a class in Computer Visualization at Stony Brook university. The program is accelerated greatly by the GPU, using a combination of fragment_program2 programs.

Features:

• It loads, displays, and saves images in the PNG format, providing several GPU-based filters to modify an image. Possible modifications include histogram equalization, Gaussian smoothing, transfer function (color mapping) manipulation in both the RGB and HSV color spaces, and noise removal.
• It supports Undo/Redo for image processing, relying on the Frame Buffer Object (FBO) extensions to OpenGL.
• It loads and displays volumetric data, as from an MRI or CT scan, using several volume visualization techniques. These techniques include a traditional slice-based rendering technique (using front-to-back, back-to-front, or max-intensity compositing), as well as a GPU-implemented, single-pass, post-interpolating ray-casting technique coupled with Blinn-Phong lighting.
• It allows for real-time specification of light color, density to opacity & color mapping, projection (orthogonal/perspective), zoom, and volume orientation.
• It implements an experimental optimization technique for the GPU ray-caster, limiting color and opacity composition only to relevant areas in a volume.

My initial implementation of the volume renderer (left hand side) ray casted the volume's bounding box, sampling at every point within it. The resulting product had a very slow drawing rate, often below 10 frames per second.

As a final, I optimized the ray casting using a technique detailed by Warren Leung, Neophytos Neophytou, and Klaus Mueller in the following paper:

SIMD-Aware Ray-Casting

This technique allows so that only points within a bounding surface of a particular user-specified density are traversed and sampled, instead of those within the entire bounding box. The optimization achieved speed-ups of 4 to 8 times, restoring near-fluid real-time interaction with the volume while maintaining true ray tracing with dynamic lighting. The speedup is demonstrated in the back/to/back footage shown above.

Papers of a similar vein can be found here:

Klaus Mueller's Volvis Research Page