This code implements the single-image illumination estimation technique introduced in

J.-F. Lalonde, A. A. Efros, and S. G. Narasimhan, "Estimating the Natural Illumination Conditions from a Single Outdoor Image," International Journal of Computer Vision, vol. 98, no. 2, pp. 123--145, Jun. 2012.

Please cite this paper if you use this code in your work.

NEW: Now much easier to run on your own images! See below.

Getting started

1. First, make sure you download the required software packages described below.

2. From the MATLAB command prompt in the mycode directory, run

   $ setPath
   $ demoEstimateIllumination
   

3. Results should display automagically!

Requirements

• MATLAB's optimization toolbox

Requires some of my software packages (available on github):

• My utils package;
• My shadowDetection package;

Requires the following 3rd-party libs (included):

• LibSVM, included in 3rd_party/libsvm-mat-3.0-1;
• Felzenszwalb et al. object detector [1], included in 3rd_party/voc-release3.1;
• Piotr Dollar's image processing toolbox, included in 3rd_party/piotr_toolbox.
• Video Compass code from Derek Hoiem, included in 3rd_party/hoiemVideoCompass;

For the paths to work "out of the box", create yourself a base directory (e.g. code), and download all of the packages in that directory. For example, code/utils, code/skyModel, code/illuminationSingleImage... The setPath function should be able to find them.

Running the code on your own images

It is now much easier to run the code on your own images! All you have to do is to set the demoMode flag to false and it will automatically compute the geometric context and the ground shadow boundaries.

You will need to make sure the following packages are installed and running (refer to their respective websites for installation instructions):

• geometric context, code available from Derek Hoiem's website;
• detected ground shadow boundaries, code available from my website.

Finally, you also need to make sure that they, as well as all their dependencies, are added to the path. See the setPath.m function for a starting point.

Compilation

Compile the object detector:

• go to 3rd_party/voc-release3.1 from inside matlab, and run 'compile'

Compile the lib-svm

• go to 3rd_party/libsvm-mat-3.0-1 from inside matlab, and run 'make'

Follow the compilation instructions of the utils package.

Notes

1. By default, this code uses the ICCV'09 version to estimate the probability of the sun given the sky cue, my previous implementation seems to give better results.

2. If you experience problems with libsvm version 3.0.1, replace the svm_model_matlab.c file with the following: https://github.com/tomz/libsvm-ruby-swig/blob/master/libsvm-3.1/matlab/svm_model_matlab.c. Make sure that the NUM_OF_RETURN_FIELD macro is set to 10. Recompile libsvm after making this change. Thanks heaps to Swaminathan Sankaranrayanan for pointing this out!

3. Alternatively, the software apparently works with libsvm version 3.1. Thanks to Lin Gu for pointing this out.

4. If matlab complains that it can't find the function xrepmat, you can either install the lightspeed package by Tom Minka, or safely replace all the xrepmat by the built-in repmat.

5. The "sky illumination" code was broken recently due to a change in the skyModel repo. Please pull! Thanks to Yannick Hold-Geoffroy for finding that bug!

Coordinates

The world coordinates (x,y,z) have the following reference frame:

     ^ y
     |
     |
     .----> x
    /
z  v

The camera is looking in the negative z direction. For convenience (or just to make things more complicated), we define azimuth=0 to be the camera viewing direction, and azimuth>0 points towards the right of the camera. Therefore, to convert from spherical to cartesian coordinates, you should use:

x = sin(zenith).*sin(azimuth);
y = cos(zenith);
z = -sin(zenith).*cos(azimuth);

References

[1] P. Felzenszwalb, D. McAllester, and D. Ramanan, "A discriminatively trained, multiscale, deformable part model," presented at the IEEE Conference on Computer Vision and Pattern Recognition, 2008.