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Week 11 - Friday. CS361. Last time. Image based effects Skyboxes Lightfields Sprites Billboards Particle systems Impostors. Questions?. Project 3. Billboard clouds. Impostors have to be recomputed for different viewing angles
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Week 11 - Friday CS361
Last time • Image based effects • Skyboxes • Lightfields • Sprites • Billboards • Particle systems • Impostors
Billboard clouds • 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 • 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
Filtering kernels • 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 • 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 • 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 and bloom • 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
Fiat Lux Directed by Paul Debevec The greatest graphics technology of… 1999
Depth of field • 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
Motion blur • 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 • 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
XNA 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
Next time… • Review
Reminders • Finish Project 3 • Due tonight before midnight • Exam 2 is next Wednesday in class • Review chapters 5 – 10
