1. Week 11 - Wednesday
CS361

2. Last time Image based effects Billboards Particle systems Skyboxes
Lightfields
Sprites
Billboards
Particle systems

3. Questions?

4. Project 3

5. Impostors
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:

6. Displacement techniques
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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. DirectX 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

17. Quiz

18. Upcoming

19. Next time…
Review

20. Reminders Finish Project 3 Exam 2 is Monday in class
Due Friday before midnight
Exam 2 is Monday in class
Friday will be review
Review chapters 5 – 10