1. Image-based Lighting Design Frederik Anrys Philip Dutré Computer Graphics Group 8 Sept. 2004

2. Overview Paint a design on a photograph of a real life object. Light intensities are determined by using the photograph.

3. 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)

4. Overview

8. Acquisition: Lights Light Stage (Debevec) 40 IColor MR RGB Led Lights Simulate the visible spectrum once calibrated

9. 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

10. Overview

11. Basis images For each light source, construct a HDR image. Linearize each HDR image into a vector. Store each vector into matrix A.

12. Design Specification 1.Start painting desired lighting design using Adobe Photoshop. 2.Adjust color, contrast, add shadows, … 3.Linearize it into vector Y.

13. Overview

14. Optimization Find x such that is minimal A y

15. 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

16. Optimization Objective function is non-linear. Constrained in added for favoring regions/pixels

17. 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.

18. Results TargetResultTargetResultTargetResult

19. Results

20. TargetResultTargetResult

21. Future Work Determining light positions/directions. Multiple camera viewpoints. Give designer interactive feedback.

22. Acknowledgements Graphics group from K.U.Leuven. Artists for lending out their work. Thank you all. Questions?

23. Applying configuration to Light Stage: Reality check Target VirtualReal