Paul Debevec / SIGGRAPH 2003 The Background The Background Capturing Light Probes in Capturing Light Probes in the Sun the Sun Paul Debevec Paul Debevec USC ICT USC ICT www.debevec.org/IBL2003 www.debevec.org/IBL2003 Guggenheim Museum, Bilbao Shoot Background Plate Shoot Background Plate Shoot Light Probe Shoot Light Probe Problem: sun intensity and color are not captured even in shortest exposure Can we recover the sun? Can we recover the sun? How bright is the sun? How bright is the sun? + α ≈ • Radius = 695,000 km • Radius = 695,000 km • Distance = 149,600,000 km • Distance = 149,600,000 km • => 0.5323 degrees in diameter seen from • => 0.5323 degrees in diameter seen from Incomplete probe alpha Unit sun Complete probe earth earth • = 0.00465 radians in radius • = 0.00465 radians in radius After diffuse convolution: • => 1/0.00465 2 = • => 1/0.00465 2 = + α ≈ sun is 46,334 sun is 46,334 times brighter times brighter than “white” than “white” Convolved alpha Convolved Convolved complete Incomplete probe Unit sun probe = Diffuse sphere! www.debevec.org/IBL2003 Page 1
Paul Debevec / SIGGRAPH 2003 Crop Diffuse and Probe Crop Diffuse and Probe Shoot Diffuse Sphere Shoot Diffuse Sphere Images Images Even better: paint the back of the mirror sphere gray and just turn it around Even better: paint the back of the mirror sphere gray and just turn it around Convert Gray Sphere into a White Convert Gray Sphere into a White Scale Probe Image to account for less- Scale Probe Image to account for less- than-100% Reflectance of the Sphere than-100% Reflectance of the Sphere Sphere using Reflectivity of Paint Sphere using Reflectivity of Paint White reference White reference White reference White reference (1, 1, 1) (1, 1, 1) (1, 1, 1) (1, 1, 1) Reflected color Reflected color (0.632, 0.647, 0.653) (0.632, 0.647, 0.653) Gray Paint Gray Paint (0.302, 0.333, 0.346) (0.302, 0.333, 0.346) Calibrate Lens Transmission Ratios Calibrate Lens Transmission Ratios Determine Sun Position in Probe Determine Sun Position in Probe (-1,1) (1,1) Diffuse white light at 160 cd/m^2 or 50 footlamberts v (u, v) = (0.414, 0.110) (Dx,Dy,Dz) = 8mm 24mm 200mm f/11, 1/60 th sec f/11, 1/60 th sec f/11, 1/60 th sec u (0.748, 0.199, 0.633) (-1,-1) (1,-1) (1.43, 1.54, 1.30) (1.73, 1.88, 1.52) (1.22, 1.34, 1.10 ) θ = arctan2(-v, u) φ = 2 arcsin( (u 2 + v 2 ) 1/2 ) (Dx, Dy, Dz) = ( sin φ cos θ , sin φ sin θ , -cos φ ) For better accuracy, should perform this measurement across entire field of view to obtain each lens’s flat field response www.debevec.org/IBL2003 Page 2
Paul Debevec / SIGGRAPH 2003 Create Probe Lighting Create Probe Lighting Create a Unit Sun Source Create a Unit Sun Source Environment Environment # unitsun.rad # Light Probe Environment probe.rad void light suncolor void colorpict lightprobe 0 7 red green blue probe.hdr spheremap.cal u v 0 0 3 46334 46334 46334 0 # Sun intensity chosen to light lightprobe glow lightprobeglow # white diffuse surface at (1,1,1) 0 0 suncolor source sun 4 1 1 1 0 0 0 lightprobeglow source sky 4 0.748 0.199 0.633 0.5323 0 0 # Sun subtended angle = 0.5323 deg. 4 0 1 0 360 RADIANCE file for unit sun RADIANCE file for light probe Solve for Sun Scaling Factor Solve for Sun Scaling Factor Adjust Sun Intensity Adjust Sun Intensity # sun.rad + α ≈ void light suncolor 0 0 3 54006 45083 32464 Incomplete probe Unit sun Diffuse Ball # obtained sun intensity as: # 46334*(1.165581,0.972998,0.700642) Subtract incomplete suncolor source sun α ≈ probe from both 0 sides to obtain: 0 4 0.748185858 0.198793344 0.633008 0.5323 α = (1.166, 0.973, 0.701) Then solve for Verify composite probe matches Verify composite probe matches diffuse ball diffuse ball + = Lit with Sun Lit with Probe Rendered Diffuse − = Real Diffuse Rendered Diffuse Avg. Error (0.5%, 0.3%, 0.2%) RMS Error = (2.2%, 1.8%, 1.3%) Background plate Background plate www.debevec.org/IBL2003 Page 3
Paul Debevec / SIGGRAPH 2003 Match-move Match-move plate & plate & model local model local scene scene Done using Façade Project Background Plate onto Local Scene Project Background Plate onto Local Scene http://www.debevec.org/Facade/ Viewed from the original viewpoint, it should look the same Viewed from the original viewpoint, it should look the same Project Light Probe onto Project Light Probe onto Render Diffuse Local Scene to create Irradiance Image Render Diffuse Local Scene to create Irradiance Image Environment Environment Divide background plate by irradiance Divide background plate by irradiance to produce local scene texture map to produce local scene texture map • Reflectance = radiance / irradiance • Reflectance = radiance / irradiance pcomb –e 'ro=0.5*ri(1)/ri(2);go=0.5*gi(1)/gi(2);bo=0.5*bi(1)/bi(2) ' pcomb –e 'ro=0.5*ri(1)/ri(2);go=0.5*gi(1)/gi(2);bo=0.5*bi(1)/bi(2) ' back.hdr local.hdr > localref.hdr back.hdr local.hdr > localref.hdr Illuminated scene without objects Illuminated scene without objects Should still look the same as the plate, although the ground is now texture-mapped and lit Should still look the same as the plate, although the ground is now texture-mapped and lit www.debevec.org/IBL2003 Page 4
Paul Debevec / SIGGRAPH 2003 Final render with objects Final render with objects Final render closeup Final render closeup Virtual shadows should match the real shadows Virtual shadows should match the real shadows Thanks! Thanks! • Andreas Wenger – CRW converter • Andreas Wenger – CRW converter • Chris Tchou – HDRShop features • Chris Tchou – HDRShop features • Greg Ward – Radiance renderer • Greg Ward – Radiance renderer • Teddy Kim – Probe assistance • Teddy Kim – Probe assistance • Maya Martinez – Rendering composition • Maya Martinez – Rendering composition • ICT Graphics Lab – Presentation comments • ICT Graphics Lab – Presentation comments http://www.debevec.org/IBL2003/ http://www.debevec.org/IBL2003/ www.debevec.org/IBL2003 Page 5
Recommend
More recommend
