Paper Summaries Any takers? Texture Mapping Announcement - PDF document

Paper Summaries  Any takers? Texture Mapping Announcement Announcement  SIGGRAPH animation screenings  Electronic Arts on campus  Every Monday  12:30pm -- 2pm  Wednesday, Sept 27th (that’s  07-1315 tonight!!!)  6:00pm - 8pm  Sponsored by RIT digital studio program  Golisano Auditorium (College Imaging Arts and Sciences) and Rochester Chapter of SIGGRAPH. Logistics Projects  Checkpoint 2  Approx 22 projects  Listing of projects now on Web  Due Today!!!  Presentation schedule  Checkpoint 3  Presentations (15 min max)  Due Monday  Last 3 classes (week 10 + finals week)  Project Proposals  Sign up  All should have received e-mail feedback.  Email me with 1 st , 2 nd , 3 rd choices  First come first served.  Please address issues (if any) 1

Remember this? Computer Graphics as Virtual Photography real camera photo Photographic Photography: scene (captures processing print light)  Bi-directional Reflectance Function processing BRDF f ( , , , ) = � � � � r i i r r camera Computer 3D tone synthetic model Graphics: models image reproduction At a given point, gives relative reflected illumination in any (focuses direction with respect to incoming illumination coming from simulated any direction lighting) Illumination Models Phong Model  Illumination model - function or algorithm used to describe the reflective characteristics of a given surface.  More accurately, function or algorithm used to approximate the BRDF. ∑ ∑ k L ( V ) = k L + k L ( S • N) + k L ( R • V) e a a d i i s i i i i ambient diffuse specular Question Texture Mapping  What if Phong (or other) Illumination  Developed in 1974 by Ed Catmull, models aren’t good enough? currently president of Pixar  Texture Mapping – use an image  Goal: Make Phong shading less plastic  Procedural Shading – program your own looking 2

Texture Mapping Texture Mapping  A means to define surface characteristics of an object using an image  Mapping a 2D image onto a 3D surface  Coordinate spaces in texture mapping  Texture space (u, v)  Object space (x o ,y o ,z o )  Screen space (x, y) Watt Texture Mapping Texture Mapping  Key to texture mapping is texture space (u,v) parameterization parameterization  3D geometry must be expressed as a function of 2 variables, u and v. object space (x o ,y o , z o )  Examples:  Planar projection  Spherical screen space (x,y)  Bi-cubic patch  Cylindrical Texture pipeline Texture pipeline example Akenine-Moller / Haines Akenine-Moller / Haines 3

Projector function Projector function  Spherical Mapping  Converts 3D point in object space (x,y,z) to 2D point in texture parameter space (u,v)  Examples:  Spherical mapping  Cylindrical mapping  Planar mapping  Parametric surface mapping Projector function Projector function – Spherical Mapping  Cylindrical mapping Texture is like a rubber sheet stretched to fit model Projector function Projector function  Spherical mapping  Bi-cubic surfaces 4

Projector function Projector function – bicubic surfaces  Texture Mapping Applets http://www.cs.brown.edu/exploratories/ freeSoftware/catalogs/texture_mapping. html Watt Corresponder function Texture Mapping - Direct Mapping  Converts from texture parameter space (u, v) to texel space.  Controls the way an image is applied  Examples:  Direct mapping  Use a portion of an image  Apply transforms  Out of range transforms Texture Mapping – Using a Portion of the Image Texture Mapping – Applying Transformation  x   u       y   Projection   Rotation   Translatio n   v  =                 z Matrix Matrix Matrix n               1 1     Foley/VanDam(745) 5

Texture mapping Texture Mapping – out of range  Aliasing  Sampling – images are discrete, not continuous.  Resolution of sampled space (in this case texture map) is not fine enough Mirror clamp border Repeat (tile) (tile) Texture mapping  Aliasing- point sampling in middle of pixel - need more! Texture Mapping – Aliasing Watt Texture Mapping Texture Mapping - Anti-aliasing  Point sample at higher resolution (sometimes  Aliasing -because of interpolation and very difficult) perspective projection  Nearest  Pick the closest texel  Linear  Take an average of surrounding texels  Mip-Mapping  Multiple textures of the same image  Use low pass filter before sampling aliased image anti-aliased image  Can sometimes use stochastic sampling to improve results 6

Texture mapping Texture Mapping  Mipmaps  Texture Map Aliasing Applet  Pre-calculate your texture map at many resolutions (or layers) http://www.nbb.cornell.edu/neurobio/la  Store all “texture layers” in a single image. nd/OldStudentProjects/cs490-  Use “appropriate” layer when performing rendering, interpolating between levels as 96to97/anson/TextureMappingApplet/ required  Mip == “multum in parvo”  Latin for “many things in a small space”  Native support in hardware. Mipmapping Texture Mapping  Mipmaps Texture pipeline When we last left our hero  Break 7

Value transform function Value Transform functions  Texture maps need not be just plain old  Texel data interpretation: RGB.  Normal displacement – Bump Mapping  Texture == data associated with an  Transparency Mask – Alpha Mapping object  Reflection – Environment Mapping  Stored in a 2D array of texels  Illumination – Light Mapping  Value transform function  Specular component – Gloss Mapping  Transforms data into value usable by the  Lighting intensities – Radiance Mapping illumination model at the shading point Texture Mapping- Bump Mapping Texture Mapping- Bump Mapping  Perturbing surface normal  Adds roughness to surfaces  Texture map represents displacements from the  Quick way to add detail to normal an object  Use perturbed normal in illumination model  Polygon remains physically flat, but appears bumpy Jim Blinn Bump Mapping Theory Texture mapping – Bump Mapping  If your eyes see light and dark  bumps  Flat surfaces reflect more light  Bumpy surfaces reflect less 8

Bump Mapping-Theory Bump Mapping  Perlin Dnoise example [Perlin85] Normal += Dnoise (point) Texture Mapping Alpha Mapping  Bump Mapping  Used to control the transparency.  Example: 3dimpact.com Texture Mapping- Environment mapping Texture Mapping- Environment mapping  Create an image, representing the reflection of  Not associated with a particular object but the world onto an object with an imaginary surface surrounding the  Use surrounding sphere or box, image is texture scene map indexed by direction of reflection ray  Specular Reflection – indexed by reflected ray  Poor-man’s ray tracing - cheaper  Diffuse - by surface normal  Transparency – refracted ray direction 9

Environment Mapping Environment Mapping spherical Cube map Texture Mapping Texture mapping  Environment mapping Reflection mapping Light Mapping Gloss Mapping  Texture map that describes illumination  The texture that controls the specular (light sources)to apply reflection color.  Modulates the the specular reflection and the environment map. flipcode.com 10

Gloss Mapping Texture Mapping  Static  Texture map image is taken under a single lighting condition  Q: What happens when lighting conditions of the scene doesn’t match that of your texture?  A: let’s go to the video tape ozone3d.net Texture pipeline Texture Mapping – Radiance Maps  Provides approximated radiance values, not simply color info, as a texture.  Radiance map not only for the distant scene, but in reflections from objects.  Radiance in map used in global  Finally obtained data is applied in illumination solution illumination equation.  Technique used in Fiat Lux Layered Texture Mapping Layered Texture Mapping  Applet http://users.interfriends.net/maurid/B umpMapping.htm 11

Multipass Texture Rendering Multipass Texture Render  Quake III Engine  Multiple textures for multiple parts of illumination model rendered on multiple  Passes 1-4: accumulating bump map  Pass 5: diffuse lighting passes.  Pass 6: base texture  Modern hardware supports up to 10  Pass 7: Specular passes on a single frame.  Pass 8: emissive lighting  Pass 9: volumetric effects  Pass 10: screen flashes Summary Summary  Texturing Pipeline  In this lecture, we assumed that textures were pre-generated and saved  Advantages of texture mapping in a file  Easy way to add complexity to a scene  Textures can also be generated on the  Hardware support fly using a function or procedure…  Issues:  But that’s for next time…  Aliasing  Limited resolution (zoom in DOOM effect)  Questions?  Static image 12