Week 13 -Wednesday Image based effects Skyboxes Lightfields - - PowerPoint PPT Presentation

Week 13 -Wednesday

 Image based effects

• Skyboxes
• Lightfields
• Sprites

 Billboards  Particle systems

 An impostor is a billboard created

• n the fly by rendering a complex
• bject to a texture

 Then, the impostor can be rendered

more cheaply

 This technique should be used to

speed up the rendering of far away

• bjects

 The resolution of the texture should

be at least:

tan(fov/2) distance 2 size

• bject

resolution screen ⋅ ⋅

 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 2mn2 time instead of m2n2 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

 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

 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 also not hard to write shader code that interpolates

between fog color and regular color based on distance

 Non-photorealistic rendering

 Read Chapter 11  Finish Assignment 4

• Due Friday before midnight

 Work on Project 3