Download presentation

Presentation is loading. Please wait.

Published byFranklin Waters Modified over 2 years ago

1
CLASS 9 ADVANCE RENDERING RAY TRACING RADIOSITY LIGHT FIELD CS770/870

2
Ray Tracing Basic idea: Cast rays out 1 per pixel. Calculate light at surface of first intersection. Does refraction – easily Does cast shadows Turner Witted (1978)

3
Witted (1979) When a ray hits a surface, it can generate up to three new types of rays: reflection, refraction, and shadow. Reflection: Trace reflection. Whatever surface is intersected becomes what is seen in the reflection. Refraction: Ray passes through, and refracted. Whatever surface is intersected becomes what is seen at that point. Shadow: Trace a ray to the light source. If blocked, compute ambient. Otherwise apply standard CG lighting [Show Witted movie]. Used a micro-film recorder.

4
Modern ray tracing. Whole bundles of rays can be used to get effects like soft shadows, more realistic ambient, etc. Used for movie cars, (first pixar ray-traced movie).

5
Ray Tracing + Radiosity

6
Radiosity (doing ambient right) Derived from heat engineering For every polygon, light input = light reflected (diffusely) + light absorbed. Some polygons also emit light Ultimately all emissions = all absorptions. Result: A huge system of equations. Must compute the influence of every polygon on every other polygon. Don Greenberg, 1986

7
The radiosity calculation

8
Methods for improving ray tracing Use bundles of rays – stockastic sampling.

9
Volume rendering.

10
Visible human Or CAT scans Or MRI scans How to look at it? Slices, The shape of organs

11
Volume rendering algorithm Used in visualization. E.g CAT scans, MRI scans A 3D volume of data. Algorithm. Compute mapping from sensed data to transparency and color. E.g. Bone is opaque and white Assume light reaches each voxel Trace rays towards the viewpoint, one for each pixel. At a set sample points along the ray, calculate orientation of density gradient. Apply lighting model. Sum light from furthest to nearest point along ray, taking opacity into account.

12
But there are no surfaces with volume rendering If we actually need to have a model of a chunk of tissue we need another method

13
Marching squares Marching cubes Consider the problem of making a contour map. At a fixed set of heights (or energy levels) we must create a continous contour. Marching squares.

14
Marching squares E.g. Contour at 50 48.3 51.253.8 50.7 Interplolate to find crossing Algorithm: for every contour value { for every square { 1. Determine case 2. Interpolate edges 3. Draw line segment }} How many unique cases?

15
15 Cases for each square.

16
Create a grid over the data set. For every square in the grid find which of the 16 cases If NOT 0000 OR 1111 Interpolate along sides to find crossing points. Then draw line segment.

17
Marching Cubes 256 cases (8 edges on the cube). 15 unique cases Polygons instead of lines

18
Used for medical imaging. Virual Colon

21
Light field sensing and rendering slides from Mark Levoy

29
Light field rendering

36
Lytro Camera Seamless blending of CGI and imagery

Similar presentations

OK

CS552: Computer Graphics Lecture 33: Illumination and Shading.

CS552: Computer Graphics Lecture 33: Illumination and Shading.

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on different types of computer softwares for resume Ppt on condition based maintenance system Ppt on railway track construction Ppt on extranuclear inheritance Ppt on file system in unix grep Ppt on bank lending interest Ppt on right to information act Ppt on obstructive jaundice Ppt on traffic light controller using verilog Ppt on limits and continuity solutions