Week 11 - Wednesday

 Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

 An impostor is a billboard created on the fly by rendering a complex object to a texture  Then, the impostor can be rendered more cheaply  This technique should be used to speed up the rendering of far away objects  The resolution of the texture should be at least:

 An impostor that also has a depth map is called a depth sprite  This depth information can be used to make a billboard that intersects with real world objects realistically  The depth in the image can be compared against the z-buffer  Another technique is to use the depth information to procedurally deform the billboard

 Impostors have to be recomputed for different viewing angles  Certain kinds of models (trees are a great example) can be approximated by a cloud of billboards  Finding a visually realistic set of cutouts is one part of the problem  The rendering overhead of overdrawing is another  Billboards may need to be sorted if transparency effects are important

 Image processing takes an input image and manipulates it  Blurring  Edge detection  Any number of amazing filters  Much of this can be done on the GPU  And needs to be (blurring shadows)  Photoshop and other programs are GPU accelerated these days

 From Project 1, you guys know all about convolution filtering kernels  I just wanted to point out that some kernels are separable  Rows and columns can be done separately  A separable m x m kernel can be run in 2mn 2 time instead of m 2 n 2 time

 Color correction takes an existing image and converts each of its colors to some other color  Important in photo and movie processing  Special effects  Time of day effects

 Tone mapping takes a wide range of luminances and maps them to the limited range of the computer's screen  To properly simulate the relative luminances  Some bright areas are made extremely bright  Some dark areas are made extremely dark  We can look for the brightest pixel and scale on that basis

 Lens flare is an effect caused by bright light hitting the crystalline structure of a camera lens  Actually happens less and less now that camera technology has improved  They can be rendered with textures  The bloom effect is where bright areas spill over into other areas  To render, take bright objects, blur them, then layer over the original scene

Directed by Paul Debevec The greatest graphics technology of… 1999

 In photography, some things are in focus and some things (either too near or too far) are blurry  When desired, this effect can be achieved by rendering the image in a range of blurred states and then interpolating between them based on z-value

 Fast moving objects exhibit motion blur in films  It doesn't often happen in real life  We have come to expect it, nevertheless  The effect can be reproduced by keeping a buffer of previously rendered frames, adding the latest frame and subtracting the first frame  Other techniques can be used to do various kinds of selective, directional blurring

 Fog effects can be used to give atmosphere or cue depth  Fog is usually based on distance (z-buffer or true distance) from the viewer  Different equations determine the effect (linear or exponential) of the fog

 The BasicEffect makes fog easy with the following members  FogEnabled Whether fog is on or off  FogColor Color of the fog  FogStart Distance (in world space) where fog starts to appear  FogEnd Distance (in world space) where fog covers everything  It's not hard to write shader code that interpolates between fog color and regular color based on distance

 Polygonal techniques  Tessellation and triangulation  Triangle strips, fans, and meshes  Simplification  Static  Dynamic  View-dependent

 Finish Project 3  Due tomorrow before midnight  Exam 2 is next Friday in class  Next Wednesday will be review  Review chapters 5 – 10