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3D –graphics and animation

Shading and Surface CharacteristicsHarri Airaksinen

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Shading and surface normals

Shading = the moment in the rendering process when visible surfaces are assigned a shading value

Shading is depend on object surface and lights Calculating the surface reflection is done by using surface

normals Common surface shading techniques include :

faceted smooth specular shading

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Faceted Shading (polygonal shading, tai constant value faceted shading )

Simplest and fastest – one shading value located in the middle of the polygon, direction is surface normal. Value tells how much light is received at the center of the polygon only. (how light it is)

take into account parameters of ambient light only (some diffuse) do not handle complex surface characteristics such as texture and

transparency well or not at all

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Smooth Shading (Gouraud shading, intensity interpolation

shading ) continuous shading value; blends throughout the visible polygons on the

surface -> idea: to average the surface normals of adjacent polygons, creating a smooth transition of shading between polygons :

sampling the amount of light reaching the surface normals in the center of polygons creating a vertex normal, averages the values of the surface normals of adjacent

polygons blending the intensifies of the vertex normals in a polygon

No reflective surfaces and only surfaces with a matte finish. take into account ambient and diffuse lighting parameters, and handle some of

the complex surface characteristics well.

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Specular Shading (normal vector interpolation shading ,Phong, Blinn,

Cook) Mirror –like shading calculates the shading at every point on the surface of a polygon

done by interpolating the vertex normals, and shading every point on the surface of the polygon by computing the relation between the angle of its normal and the angle of the incident light

can handle ambient, diffuse, and specular lighting, and detailed surface characteristics extremely well

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Surface Shader

Material editor tool for simulating materials

The shaders includes: reflectivity color texture transparency

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Material Editor and 3D Studio Max

Double-click Drag&Drop

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Surface libraries or material databases

Differences between applications

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Surface Layers

• by adding layers and compoundingtheir effects to determine the finallook of the surface

• Makes it possible to build complexsurface materials

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Image mapping

2D image and mapping it on the surface of a three-dimensional object by projecting or wrapping

Very efficiently simulate not only the texture of a three-dimensional surface, but also other surface attributes such as reflectivity, transparency, and roughness

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Image mapping

Images maps can modulate the surface characteristics by linking the brightness or color of a pixel in the image map to the characteristics of the point in the surface where that pixel is mapped -> the brightness of a pixel in an image map can control the reflectivity of the point on the surface where the pixel is mapped, or its color, or its transparency.

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Creating the Map

2D -images that can be mapped onto 3D -surfaces: painted images photographic images abstract patterns (rule-based)

Input devices: recording a live image with a digital camera scanning an existing photograph painting with a flatbed laser digital scanner image libraries (software vendors, net …)

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Own image maps and 3D Studio Max

Double_click

Drag & Drop

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Projection Methods

• How the picture/pattern is projected over the 3D object?

Modifier UV-mapping

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Projection Methods

Most useful projection methods include: The flat projection method (planar) applies maps onto surfaces

in a flat way - identical results as long as the three-dimensional surface is parallel to the projection plane

The cubical projection method (box) is a variation of the flat projection method that repeats the map on each of the six sides of a cube - effective with cubes but only as long as one of the planes of the cube is parallel to the projection plane

The cylindrical projection method applies maps onto surfaces by wrapping the sides of the map around the shape until the two ends of the map meet behind the object – bottom & top problem

The spherical projection applies a rectangular map by wrapping it around a surface until the opposite sides meet, and then pinching it at the top and bottom and stretching it until the entire object is covered

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Projection Methods- wrapping -

Textures to be projected onto 3D objects in a straight way, but also be stretched until the four sides of the map are pressed against each other

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Positioning the Map- local coordination -

Not use XY –coordination, but surface local coordination system, U, V, W

U = horizontal, V = Vertical Offset control how the picture islocated on the surface, example.0.5. and 0.5 locate the picture in half wayin both directionn

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Positioning the Map

Tiling

Map Blending = mixing images

Using tiling: 3 times U- and V- axels.

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Image map as a mask- Blending with matting techniques -

• Using ALPHA –image to mask holes to object surface•Alpha –channel use:

• a CREYSCALE image file a that is linked to an image map• saved with an image file in the form of a fourth channel in a RGB image • determine degree of blending of the image map with a surface based on• the intensity of brightness values of the pixels file used=alpha channels

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Surface Reflectivity

The basic three types of surface reflectivity are: ambient diffuse specular

Surface reflectivity types: Matte surfaces can be simulated by using a combination of ambient

and diffuse reflections. Metallic surfaces can be simulated with ambient and specular

reflections. Plastic surfaces are typically simulated with a combination of

ambient, diffuse, and specular reflections

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Environment Maps

They are special type of reflection map because they reflect not only the objects surrounding the mapped object, but also the environment surrounding the reflective surfaces

Environment maps can

be animated: if something

happened around the

object, the movement is

reflected to the object

surface

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Environment Maps

Spherical environment mapping

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Environment Maps

Cubical environment mapping

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Environment Maps – 3D Studio Max

Rendering Environment

2-click

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Environment Maps – 3D Studio Max

Render

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Surface textures

Texturing techniques can be grouped: Visual textures are flat simulations of 3D -texture and no affect the geometrical

surface of the object; they look textured but they are not. Example, a visual texture bricks is like brick wallpaper, and different from a real

wall of bricks with relief textures that can be felt by touch. A benefit of using visual textures is make possible the creation of complex and rich textures with a minimal investment of polygons. Like color and procedural maps, environment, bump, and transparency maps

Spatial textures exist in 3Dand affect the spatial integrity of the smooth surface of an object.

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Bump Maps

1978, developed by James Blinn Simulates the bumps or wrinkles in a surface without the

need for geometric modifications to the model The surface normal of a given surface is perturbed

according to a bump map. The perturbed normal is then used instead of the original normal when shading the surface using the Lambertian technique

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Displacement Maps

Provide a unique way to use an image map to actually modify not only the shading but also the geometry of the surface being mapped

Displacement maps are often used to create 3D terrain. Terrains can be built with displacement maps that are based on photographic images of aerial views where the different elevations are coded with different colors or shades of gray.

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Three-Dimensional Procedural Texture Maps

Solid textures if you cut the object, cutline is presented in “correct” way

Rules control texture creation

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Transparency

Surface feature how the light penetrate the object Can be faked or using ray tracing and real materials transparency map consists of a monochromatic 2D -image that is

applied to a 3D -surface with the purpose of making all or some of the surface transparent

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Controlling environment-dependent variables

Antialiasing – When the spatial resolution of an image is too low, its details are often lost

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Controlling environment-dependent variables

Fast movement Motion Blur Needed feature when animation include fast object

movements not a default setup Usually speeds of 1/250th of a second are necessary to

freeze fast-moving objects. 30 fps (frame per sec = 1/30 seconds per picture)

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Controlling environment-dependent variables

Fog system add white color or transparency based on object and camera distance - depth-fading

Needed feature not a default setup