Lecture 15 - Warping and Morphing I

# Lecture 15 - Warping and Morphing I - Interactive Computer...

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Interactive Computer Graphics: Lecture 15 Warping and Morphing

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Warping and Morphing Graphics Lecture 15: Slide 2 What is – warping ? – morphing ? ?
Warping and Morphing What is – warping ? – morphing ? ? Graphics Lecture 15: Slide 3

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Warping and Morphing What is – warping ? – morphing ? Graphics Lecture 15: Slide 4
Warping and Morphing: Slide 5 Warping • The term warping refers to the geometric transformation of graphical objects (images, surfaces or volumes) from one coordinate system to another coordinate system. • Warping does not affect the attributes of the underlying graphical objects. Attributes may be – color (RGB, HSV) – texture maps and coordinates – normals, etc.

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Morphing • The term morphing stands for metamorphosing and refers to an animation technique in which one graphical object is gradually turned into another. • Morphing can affect both the shape and attributes of the graphical objects. Graphics Lecture 15: Slide 6
Warping and Morphing What is – warping ? – morphing ? Graphics Lecture 15: Slide 7

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Morphing = Object Averaging The aim is to find an average between two objects Not an average of two images of objects …but an image of the average object ! How can we make a smooth transition in time? Do a weighted average over time t How do we know what the average object looks like? Need an algorithm to compute the average geometry and appearance Graphics Lecture 15: Slide 8
Averaging P Q v = Q - P P + 0.5 v = P + 0.5( Q P ) = 0.5 P + 0.5 Q P + 1.5 v = P + 1.5( Q P ) = -0.5 P + 1.5 Q (extrapolation) Linear Interpolation (Affine Combination): New point a P + b Q , defined only when a+b = 1 So a P + b Q = a P +(1- a ) Q What’s the average of P and Q ? Graphics Lecture 15: Slide 9

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Image blending Determines how to combine attributes associated with geometrical primitives. Attributes may include – color – texture coordinates – normals • Blending – cross-dissolve – adaptive cross-dissolve – alpha-channel blending – z-buffer blending
Image blending: Cross-dissolve Blending with cross-dissolve: – intensities – RGB space – HSV space – texture space B A I t I t I + = ) 1 (

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Image blending: Cross-dissolve RGB Texture
Morphing using cross-dissolve But what is the images are not aligned? Graphics Lecture 15: Slide 13

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Morphing using warping and cross-dissolve Align first, then cross-dissolve Graphics Lecture 15: Slide 14
Morphing = (warping) 2 + blending

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Morphing GenerateAnimation(Image 0 , Image 1 ) begin foreach intermediate frame time t do Warp 0 = WarpImage(Image 0 , t) Warp 1 = WarpImage(Image 1 , t) foreach pixel p in FinalImage do Result(p) = (1- t )Warp 0 + t Warp 1 end end end
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