Modeling View-Dependent Surface Point Radiance with Parameter Maps

Mortensen, Bjarne ; Andersen, Jens

4. term

Vision, Graphics and Interactive Systems, Master

2007

149

Denne afhandling undersøger, hvordan man kan indfange, modellere og gengive virkelige overflader i computergraphics, så både synsvinkelafhængigt udseende (at overflader ser forskellige ud fra forskellige vinkler) og fine geometriske detaljer bevares. Vi fotograferer et tæt gitter af punkter på overfladen fra mange retninger med high dynamic range (HDR) billeddannelse og registrerer radiansen (lyset, der forlader hvert punkt) for hver synsretning. Derefter tilpasser vi kompakte, punktvise parametriske modeller, der beskriver, hvordan radiansen varierer med retningen. To alternativer afprøves: en modificeret Phong-reflektionsmodel (en tilpasset version af en klassisk lysformel) og sfæriske harmoniske funktioner (matematiske funktioner, der effektivt beskriver retningsvariation). For at rendere overfladerne implementerer vi skræddersyede vertex- og fragment-shadere i OpenGL, uploader modelparametre og programmer til grafikkortet (GPU) og rekonstruerer det synsvinkelafhængige udseende på simpel geometri i en interaktiv realtidsapplikation. Testene viser styrker og svagheder ved begge modeller og giver praktiske råd om, hvordan prøvetagningen bør udføres for de bedste resultater.

This thesis explores how to capture, model, and reproduce real-world surfaces in computer graphics while preserving view-dependent appearance (how a surface looks different from different angles) and fine geometric details. We photograph a dense grid of surface points from many directions using high dynamic range (HDR) imaging and record the radiance (the light leaving each point) for each view. We then fit compact, per-point parametric models that describe how radiance varies with direction. Two alternatives are tested: a modified Phong reflection model (an adapted version of a classic lighting formula) and spherical harmonics (mathematical functions that efficiently represent directional variation). To render the surfaces, we implement custom vertex and fragment shaders in OpenGL, upload the model parameters and programs to the graphics card (GPU), and reconstruct the view-dependent appearance on simple geometry in an interactive, real-time application. The tests reveal strengths and weaknesses of both models and provide practical guidance on how to sample the surfaces for the best results.

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