Texture Mapping Logistics Checkpoint 2 Mostly graded. Note on grading -- Regaining points Checkpoint 3 Due Monday Project Proposals All should have received e-mail feedback. 1
Logistics Checkpoint 2 Another means for finding equation of a plane Using determinants. See: http://local.wasp.uwa.edu.au/~pbourke/geometry/planeeq/ Logistics Grad students Please send topic of grad report. 2
Projects Proposals Proposal due before break (please get yours in if not submitted) Feedback on proposals -- mycourses Web sites please. 23 projects (4-5 more expected) Projects Presentations: Dates: Week 9: Wed, Feb 13 (sorry Radiosity) Week 10: Mon, Feb 18 Week 10: Wed, Feb 20 Finals Week / Week 11: Mon, Feb 25 15 minutes / presentation Schedule on Web by next class Please send me choice of time/day 3
Computer Graphics as Virtual Photography real camera photo Photographic Photography: scene (captures processing print light) processing camera Computer 3D synthetic tone model Graphics: models image reproduction (focuses simulated lighting) Remember this? Bi-directional Reflectance Function BRDF f ( , , , ) = � � � � r i i r r At a given point, gives relative reflected illumination in any direction with respect to incoming illumination coming from any direction 4
Illumination Models 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. Phong Model ∑ ∑ 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 5
Question What if Phong (or other) Illumination models aren’t good enough? Texture Mapping – use an image Procedural Shading – program your own Texture Mapping Developed in 1974 by Ed Catmull, currently president of Pixar Goal: Make Phong shading less plastic looking 6
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) Texture Mapping Watt 7
Texture Mapping Key to texture mapping is parameterization 3D geometry must be expressed as a function of 2 variables, u and v. Examples: Planar Spherical Bi-cubic patch Cylindrical Texture Mapping texture space (u,v) parameterization object space (x o ,y o , z o ) projection screen space (x,y) 8
Texture pipeline Akenine-Moller / Haines Texture pipeline example Akenine-Moller / Haines 9
Projector function 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 Spherical Mapping 10
Projector function – Spherical Mapping Texture is like a rubber sheet stretched to fit model Projector function Cylindrical mapping 11
Projector function Spherical mapping Projector function Bi-cubic surfaces 12
Projector function – bicubic surfaces Watt Projector function Texture Mapping Applets http://www.cs.brown.edu/exploratories/ freeSoftware/catalogs/texture_mapping. html 13
Corresponder function 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 - Direct Mapping 14
Texture Mapping – Using a Portion of the Image Texture Mapping – out of range Mirror clamp border Repeat (tile) (tile) 15
Texture mapping Aliasing Sampling – images are discrete, not continuous. Resolution of sampled space (in this case texture map) is not fine enough Texture mapping Aliasing- point sampling in middle of pixel - need more! 16
Texture Mapping – Aliasing Watt Texture Mapping Aliasing -because of interpolation and perspective projection aliased image anti-aliased image 17
Texture Mapping - Anti-aliasing Point sample at higher resolution (sometimes very difficult) 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 Can sometimes use stochastic sampling to improve results Texture mapping Texture Map Aliasing Applet http://www.nbb.cornell.edu/neurobio/la nd/OldStudentProjects/cs490- 96to97/anson/TextureMappingApplet/ 18
Texture Mapping Mipmaps Pre-calculate your texture map at many resolutions (or layers) Store all “texture layers” in a single image. Use “appropriate” layer when performing rendering, interpolating between levels as required Mip == “multum in parvo” Latin for “many things in a small space” Native support in hardware. Mipmapping 19
Texture Mapping Mipmaps Texture pipeline Break 20
When we last left our hero Value transform function Texture maps need not be just plain old RGB. Texture == data associated with an object Stored in a 2D array of texels Value transform function Transforms data into value usable by the illumination model at the shading point 21
Value Transform functions Texel data interpretation: Normal displacement – Bump Mapping Transparency Mask – Alpha Mapping Reflection – Environment Mapping Illumination – Light Mapping Specular component – Gloss Mapping Lighting intensities – Radiance Mapping Texture Mapping- Bump Mapping Adds roughness to surfaces Quick way to add detail to an object Polygon remains physically flat, but appears bumpy Jim Blinn 22
Texture Mapping- Bump Mapping Perturbing surface normal Texture map represents displacements from the normal Use perturbed normal in illumination model Texture mapping – Bump Mapping 23
Bump Mapping Theory If your eyes see light and dark bumps Flat surfaces reflect more light Bumpy surfaces reflect less Bump Mapping-Theory 24
Bump Mapping Perlin Dnoise example [Perlin85] Normal += Dnoise (point) Texture Mapping Bump Mapping 25
Alpha Mapping Used to control the transparency. Example: 3dimpact.com Texture Mapping- Environment mapping Create an image, representing the reflection of the world onto an object Use surrounding sphere or box, image is texture map indexed by direction of reflection ray Poor-man’s ray tracing - cheaper 26
Texture Mapping- Environment mapping Not associated with a particular object but with an imaginary surface surrounding the scene Specular Reflection – indexed by reflected ray Diffuse - by surface normal Transparency – refracted ray direction Environment Mapping 27
Environment Mapping spherical Cube map Texture Mapping Environment mapping 28
Texture mapping Reflection mapping Light Mapping Texture map that describes illumination (light sources)to apply flipcode.com 29
Gloss Mapping The texture that controls the specular reflection color. Modulates the the specular reflection and the environment map. Gloss Mapping ozone3d.net 30
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 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 illumination solution Technique used in Fiat Lux 31
Texture pipeline Finally obtained data is applied in illumination equation. Layered Texture Mapping 32
Layered Texture Mapping Applet http://www.neilwallis.com/java/bump 1.htm Multipass Texture Rendering Multiple textures for multiple parts of illumination model rendered on multiple passes. Modern hardware supports up to 10 passes on a single frame. 33
Multipass Texture Render Quake III Engine Passes 1-4: accumulating bump map Pass 5: diffuse lighting Pass 6: base texture Pass 7: Specular Pass 8: emissive lighting Pass 9: volumetric effects Pass 10: screen flashes Summary Texturing Pipeline Advantages of texture mapping Easy way to add complexity to a scene Hardware support Issues: Aliasing Limited resolution (zoom in DOOM effect) Static image 34
Summary In this lecture, we assumed that textures were pre-generated and saved in a file Textures can also be generated on the fly using a function or procedure… But that’s for next time… Questions? 35
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