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MATLAB implementation of the Perez physically-based sky model.
Avoids problems with camera is looking close to zenith (horizon line is at infinity!). Can be converted back and forth anyway.
This is a MATLAB implementation of the Perez sky model  that we've re-parameterized as a function of common camera parameters, as explained in our IJCV 2010 paper . See the following website for more information: http://graphics.cs.cmu.edu/projects/sky/ === TEST FILE === Use the file 'synthesizeSky.m' as a starting point. === SKY MODEL === These files synthesize the sky model based on camera parameters as inputs: - exactSkyModel.m: Synthesizes the full sky model; - exactGradientModel.m: Synthesizes only the "gradient" part of the sky model; - exactSunModel.m: Synthesizes only the "sun" part of the sky model. These files synthesize the sky model based on angles as inputs (Perez sky model): - perezSkyModel.m: Synthesizes the full sky model; - perezGradientModel.m: Synthesizes only the "gradient" part of the sky model; - perezSunModel.m: Synthesizes only the "sun" part of the sky model. Useful files that convert from pixel coordinates to angles: - pixelAzimuthAngle.m: Converts from pixels to azimuth angle; - pixelZenithAngle.m: Converts from pixels to zenith angle. === TURBIDITY === These files deal with converting the turbidity to the Perez weather coefficients (in 3 channels in xyY color space, as in ): - convertTurbidityToSkyParams.m: Converts turbidity to the weather coefficients; - getTurbidityMapping.m: Returns the turbidity mapping between the weather coefficients in each channel. === REFERENCES ===  R. Perez, R. Seals, and J. Michalsky, "All-weather model for sky luminance distribution -- preliminary configuration and validation," Solar Energy, vol. 50, no. 3, pp. 235--245, Mar. 1993.  J.-F. Lalonde, S. G. Narasimhan, and A. A. Efros, "What do the sun and the sky tell us about the camera?," International Journal of Computer Vision, vol. 88, no. 1, pp. 24--51, May 2010.  A. J. Preetham, P. Shirley, and B. Smits, "A practical analytic model for daylight," presented at the Proceedings of ACM SIGGRAPH 1999, 1999. === CHANGELOG === 09/18/12: Now using github! See commit messages for changelogs. 09/21/11: Added missing file 'exactGradientModelRatio.m'. Thanks to A. Ravichandran for pointing this out!