Class7

Class7 - Class 7. Screen-Space Interpolation with...

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Class 7. Screen-Space Interpolation with Perspective Correction Ulrich Neumann CS580 (Computer Graphics Rendering)
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Problem Can we interpolate image space parameters over triangles in screen space? NO : accurate surface parameter interpolation has to take perspective into account. Line on screen in perspective shrinks most of the range into the last few pixels.
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Checkerboard Example Checkerboard defined as integer grid red over odd/odd (o, o) and even/even (e, e) intervals black over odd/even intervals (e, o), (o, e) Image midpoint is not actual midpoint of checkerboard Straight line along diagonal stays straight under perspective Linear Interpolation Perspective Interpolation Mid-image checkerboard interpolation point is not mid-object Correct mid-checkerboard interpolation to mid-object 0,0 2,2 2,0 0,2 0,1 2,1 1,0 1,2
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Parameter Interpolation Similarly, linear interpolation of affine (image space) parameters like Z give wrong result Interpolation of perspective Z is correct (all HW so far) we can recover image space result if we Xform perspective Z back to image (affine) space after interpolation Effect is modest for scene like teapot where Z range is small, or with narrow FOV Roads to horizon, grazing angles on slightly curved surface like a car hood, and wide FOV cameras produce a more dramatic impact Need correct interpolation of u,v texture coords in HW5 Z=1 Z = 11 Z = 21 a b c Z= -d Z= 0
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This note was uploaded on 04/22/2010 for the course CS 580 at USC.

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Class7 - Class 7. Screen-Space Interpolation with...

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