Estimating incident illumination in outdoor scenes

In the paper named "Estimating Surface Reflectance Properties of a Complex Scene under Captured Natural Illumination", it explains the way to estimate the incident illumination in outdoor scenes.



  • diffuse gray ball
    • The reflectivity is (0.30, 0.31, 0.32).
  • mirror ball
    • This ball is used to capture the sky image. Its reflective is 0.52.
  • black glossy ball
    • This is used to estimate the direction of the sun.
  • It is difficult to get the value of the sun's bright intensity, because it tends to saturate the mirrored sphere image.
  • So, this paper uses these steps to get the sun's bright intensity.



  1. Estimate the sun direction from the black glossy ball.
  2. Convolve the mirror ball value and get the irradiance map as D'.
  3. Render the sun's diffuse lighting of sphere as D*.
  4. If we assume the sun intensity as α and the diffuse gray ball value as D, then D' + α D* should be D.
  5. So, by changing the value of the α, we can estimate the sun intensity α.
  • If you write down the equation, it becomes like this.
convolve ( mirror_ball_pixel_value / ( 0.52, 0.52, 0.52 )) + sun_intensity * dot( sun_direction, surface_normal ) = diffuse_gray_ball_pixel_value / ( 0.30, 0.31, 0.32 )