Computer Graphics Inf 4MSc Computer Graphics Lecture Notes

Computer Graphics Inf 4/MSc Computer Graphics Lecture Notes #16 Image-Based Lighting

Computer Graphics Global Illumination and Based Lighting Inf 4/MSc Image- • Traditional Computer Graphics involves: – Modelling with matter: geometry with reflectance properties. • Image-Based Lighting allows: – Combination of real and synthetic graphics with consistent illumination, using images as light sources. – Extension of Environment mapping 13/11/2007 2

Computer Graphics Environment Mapping • Computing the color according to the reflection vector • No self-shadowing, no inter-reflection Inf 4/MSc

Computer Graphics Inf 4/MSc Image Based Lighting • Add models or objects to scenes and allow them to be manipulated in the scenes. • Modelling with light allows added objects to be illuminated consistent with image existent lighting - photorealistic inclusions. • We start with the answer by finding the scene illumination. 13/11/2007 4

Computer Graphics Inf 4/MSc Image Based Lighting • Real Scene (all pictures P. Debevec 98 -99) • Goal: place synthetic objects on table 13/11/2007 5

Computer Graphics Inf 4/MSc Extracting scene lighting • Capture illumination using illumination sphere 13/11/2007 6

Computer Graphics Inf 4/MSc Image Based Lighting Real scene 13/11/2007 7

Computer Graphics Inf 4/MSc Image Based Lighting captured illumination field 13/11/2007 8

Computer Graphics Inf 4/MSc Image Based Lighting light based model synthetic objects local scene Real scene 13/11/2007 9

Computer Graphics Inf 4/MSc Image Based Lighting • Use global illumination - compute effects of synthetic objects on local scene light based model synthetic objects (brdf known) 13/11/2007 local scene (brdf estimated) 10

Computer Graphics Inf 4/MSc Image Based Lighting • Render into the scene background 13/11/2007 11

Computer Graphics Inf 4/MSc Image Based Lighting • Render synthetic objects 13/11/2007 12

Computer Graphics Inf 4/MSc Image Based Lighting • Effect of local scene on real scene 13/11/2007 13

Computer Graphics Inf 4/MSc Image Based Lighting • Add differences to image 13/11/2007 14

Computer Graphics Some more results Inf 4/MSc

Computer Graphics Inf 4/MSc Light Probe Images • Spherical Environment Maps • In most digital images, pixel values aren’t proportional to the light levels in the scene. – light levels are encoded nonlinearly so they appear either more correctly or more pleasingly on CRTs

Computer Graphics High-Dynamic Range Photography Inf 4/MSc • Standard digital images typically represent only a small fraction of the dynamic range —the ratio between the dimmest and brightest regions accurately represented— present in most realworld lighting environments. • The bright light saturates the pixel colour • Need a high dynamic range image which can be produced by combining images of different shutter speed

Computer Graphics High-Dynamic Range Photography Inf 4/MSc

Computer Graphics Inf 4/MSc HDR images

Computer Graphics Inf 4/MSc

Computer Graphics Inf 4/MSc Comparison: Radiance map versus single image

Computer Graphics Inf 4/MSc Eyes For Relighting • Extracting environment maps from eyes for use in integrating and relighting scenes • Apply IBL to the 3 D objects added into the image • http: //www. youtube. com/watch? v=Mll. TSof. Xt 8 E

Computer Graphics Inf 4/MSc Shape from Shading • Obtaining the 3 D shape from an image • Assuming Lambertian reflection • Can recover the normal vector if we cast the Example: sphere light from 3 different directions (lit from left) N L Object

Computer Graphics • Integrate the normals over the surface to compute the 3 D surface • We can also estimate the colour information and use this for texture Inf 4/MSc

Surface inserted into new scenes Inf 4/MSc Computer Graphics • lit according to the global illumination of that scene. • This illumination can of course come from eyes!

Computer Graphics Inf 4/MSc Acquiring the Reflectance Field of a Human Face • Simulating reflectance on human faces requires a lot of effort and computation – Need to acquire the reflectance model – Subsurface scattering • Instead of simulating the global illumination, we can simply illuminate the face by real-lights from different directions • Creating images of arbitrary light conditions by combining the captured data

Computer Graphics The Light Stage: Inf 4/MSc 60 -second exposure

Computer Graphics Light Stage Data Inf 4/MSc Original Resolution: 64 32 Lighting through image recombination: Haeberli ‘ 92, Nimeroff ‘ 94, Wong ‘ 97

Computer Graphics Reflectance Functions Inf 4/MSc

Computer Graphics Inf 4/MSc Lighting Reflectance Functions 1 normalized light map reflectance function lighting product rendered pixel

Computer Graphics Inf 4/MSc References • Rendering Synthetic Objects into Real Scenes, SIGGRAPH 98 • Acquiring the Reflectance Field of a Human Face, SIGGRAPH 2000 http: //www. debevec. org • Eyes For Relighting, Nishino SIGGRAPH 2004 13/11/2007 31