Bounding Volume Hierarchy

The space within the scene is divided into a grid. When a ray travels through a scene, it only passes a few boxes within the grid. Testing only the objects within these grid boxes can save a lot of time.

Spatial Subdivisions

There may be many objects in a single grid square. Many other squares may have nothing in them.

This technique can be used to vary the size of grid squares, creating more where there is likely to be an intersection and less where there isn't.

Non Uniform Spatial Distribution

The red arrow in the image only crosses 7 boxes and only one object needs to be tested for intersections.

Anti- Aliasing

• Anti aliasing improves the appearance of polygon edges, so they are not "jagged" but are smoothed out on the screen.• Incurs a performance cost for the graphics card and uses more video memory

Aliasing vs Anti- Aliasing

It involves casting more than one regularly spaced sample per pixel and using the average of the results for the pixel intensity.

Types :Adaptive Stochastic

Supersampling

• Each pixel to be traced has a primary ray cast through each of its corners.

• If the intensity of any of the four rays varies from the other three, then the pixel is split into four rectangular portions.

Adaptive Supersampling

• Any quadrant for which the new rays display any significant difference are further subdivided and the process is repeated for that quadrant.

• This process can be repeated an any number of times.

Contd.

• Also known as Random supersampling• Location of the ray can be varied, instead of

using a grid• Due to the irregularity of the pattern,

samples end up being unnecessary in some areas of the pixel and lacking in others

Stochastic Supersampling

Adaptive vs Stochastic

• Environment mapping gives these reflections more cheaply with little loss of accuracy

• is an efficient image-based lighting technique for approximating the appearance of a reflective surface by means of a pre-computed texture image.

Environment Mapping

Cube with environment mapping

• In real life soft shadows are formed, have 2 parts an umbra and a penumbra

• Hard shadows form harsh edges

• But in real life, lights are not mathematical points and hence cast soft shadows.

Soft Shadows

Soft Shadow

Hard Shadow

Light travels through an objects surface, instead of bouncing off

It’s a diffusion phenomenonMost non metals show translucency

Translucency

• It is a way to enhance the realism of a rendered animation by simulating the way a real world camera works.

• Motion blur is the apparent streaking of rapidly moving objects in a still image or a sequence of images such as a movie or animation.

• Due to lower shutter speeds, image of a scene over a prolonged period if time is captured.

Motion Blur

Without motion blur

With motion blur

• Used in 3D graphics , computer graphics, video games etc.

• Animated movies – for more realistic rendering

• Biophotonics - emission, detection, absorption, reflection, modification, and creation of radiation from biomolecular, cells, tissues, organisms and biomaterials

Applications of Ray Tracing

Current problems :◦ Immense computational requirements◦ Slow processing◦ Not as efficient as rasterization

• May be used to produce better graphics than those produced by rasterization

• Can be very efficient on multiple core processors, as it can be parallelized very easily.

Ray Tracing – The Future

• www.cs.unc.edu/~rademach/xroads-RT/RTa • Wikipedia’s Ray Tracing article.

http://en.wikipedia.org/wiki/Ray_tracing • www.breault.com/.../ma_lp_001_raytracing_medicine_english.pdf • paulbourke.net/miscellaneous/aliasing/

Books Computer Graphics- Zhigang Xiang, Roy A Plastock. Schaum's Series. “An Introduction To Ray Tracing” – Andrew S.

Glassner

References

Thank You