Image-based Lighting Design Frederik Anrys Philip Dutré Computer Graphics Group 8 Sept. 2004
Overview Paint a design on a photograph of a real life object. Light intensities are determined by using the photograph.
Previous Work Lighting Design –Sketching highlights and shadows to position lights (Poulin ‘97) –Painting with Light (Schoeneman ‘93) Image-based Relighting –A lighting reproduction approach to live-action composition (Debevec ‘02)
Overview
Acquisition: Lights Light Stage (Debevec) 40 IColor MR RGB Led Lights Simulate the visible spectrum once calibrated
Acquisition: Camera Canon EOS D30 digital Camera High Dynamic Range (HDR) Images Luminance values are represented in full floating point values instead of 8-bit RGB values used for display. No compression using a response curve. Usually constructed by taking a series of photographs
Overview
Basis images For each light source, construct a HDR image. Linearize each HDR image into a vector. Store each vector into matrix A.
Design Specification 1.Start painting desired lighting design using Adobe Photoshop. 2.Adjust color, contrast, add shadows, … 3.Linearize it into vector Y.
Overview
Optimization Find x such that is minimal A y
Optimization Ax resides in luminance space y resides in display space F converts Ax to display space –Why? The L2 norm is well defined and fast method for comparing images in display space. –F is standard Gamma correction function
Optimization Objective function is non-linear. Constrained in added for favoring regions/pixels
Optimization The problem is solved by Sequential Quadratic Programming (SQP). Gradient is computed analytically. Optimization takes 15 seconds to complete: –40 lightsources (3 channels). –P3-1.2 Ghz computer.
Results TargetResultTargetResultTargetResult
Results
TargetResultTargetResult
Future Work Determining light positions/directions. Multiple camera viewpoints. Give designer interactive feedback.
Acknowledgements Graphics group from K.U.Leuven. Artists for lending out their work. Thank you all. Questions?
Applying configuration to Light Stage: Reality check Target VirtualReal