Method for simulating the illumination of an indoor scene observed by a camera illuminated by outdoor light and system
A method for simulating, at an instant, the illumination of an indoor scene observed by a camera and being illuminated by outdoor light, the method comprising: a first preliminary phase including: obtaining a reflectance map of the scene elaborating normalized radiosity maps for the contribution of the sky and the ground, a second phase carried out within a first given duration from the instant including: obtaining the position of the sun, obtaining a normalized radiosity map for the contribution of the sun, a third phase, including: acquiring an image of the scene, determining brightness scale parameters for the ground, the sky, and the sun. The disclosure also proposes tracking the camera position.
1. A method for simulating, at an instant, an illumination of an indoor scene observed by a camera and being illuminated by outdoor light, the method comprising:
a first preliminary phase including:
obtaining a 3D geometric model of the scene,
obtaining image information of the scene,
obtaining a reflectance map of the scene for a contribution of outdoor illumination to the scene based on the 3D geometric model of the scene and the image information of the scene, wherein obtaining the reflectance map comprises considering a plurality of light sources arranged on a sphere centered on the scene,
elaborating a normalized radiosity map for a contribution of the sky to the outdoor illumination based on the reflectance map wherein elaborating the normalized radiosity map for the contribution of the sky to the outdoor illumination based on the reflectance map comprises only considering the light sources in the upper half of the sphere,
elaborating a normalized radiosity map for a contribution of a ground to the outdoor illumination based on the reflectance map wherein elaborating the normalized radiosity map for the contribution of the ground to the outdoor illumination based on the reflectance map comprises only considering the light sources in the lower half of the sphere,
a second phase carried out within a first given duration from the instant including:
obtaining a position of the sun using geolocation, time, and orientation of the scene,
obtaining a normalized radiosity map for a contribution of the sun to the outdoor illumination based on the position of the sun and the reflectance map,
a third phase carried out within a second given duration from the instant, shorter than the first given duration, including:
acquiring at least one image of the scene,
determining from the at least one image a brightness scale parameter for the contribution of the ground, a brightness scale parameter for the contribution of the sky, and a brightness scale parameter for the contribution of the sun,
rendering a normalized image of the scene for the contribution of the sky to the outdoor illumination of the scene based on the normalized radiosity map for the contribution of the sky to the outdoor illumination,
rendering a normalized image of the scene for the contribution of the ground to the outdoor illumination of the scene based on the normalized radiosity map for the contribution of the sky to the outdoor illumination, and
rendering a normalized image of the scene for the contribution of the sun to the outdoor illumination of the scene based on the normalized radiosity map for the contribution of the sky to the outdoor illumination.
2. The method of claim 1 , wherein the preliminary phase comprises a ray-tracing step to determine a visibility of each vertex of the 3D geometric model, the method further comprising using the visibilities to obtain the normalized radiosity maps for the contribution of the sky, of the ground, and of the sun.
3. The method of claim 1 , wherein obtaining the reflectance map comprises using image information of the scene acquired when there is no direct sunlight entering the scene.
4. The method of claim 1 , wherein obtaining the reflectance map comprises using image information of the scene acquired when there is direct sunlight entering the scene at different instants associated with different positions of the sun.
5. The method of claim 1 , wherein determining from the image a brightness scale parameter for the contribution of the ground, a brightness scale parameter for the contribution of the sky, and a brightness scale parameter for the contribution of the sun, comprises minimizing a difference between the image and a linear combination of products of each brightness scale parameter with the corresponding normalized image.
6. The method of claim 1 , wherein the third phase comprises acquiring a plurality of images of the scenes at different instants and determining the brightness scale parameters uses the plurality of images.
7. The method of claim 1 , comprising elaborating an image of the scene from the normalized images of the scene and the brightness scale parameters.
8. The method of claim 7 , wherein the method for simulating the illumination of an indoor scene is the method in accordance with claim 7 , and wherein tracking is performed on the image elaborated from the normalized images of the scene and the brightness scale parameters.
9. A method for tracking the position of a camera observing a scene over a plurality of instants, using the simulated illumination of the indoor scene by the method for simulating the illumination of an indoor scene in accordance with claim 1 at every instant of the plurality of instants.
10. A system comprising a camera and a control unit configured to perform the method according to claim 1 .
11. A nontransitory recording medium readable by a computer and having recorded thereon a computer program including instructions for executing the steps of a method according to claim 1 .