Risson, Valéry (2001) Application de la morphologie mathématique à l'analyse des conditions d'éclairage des images couleur. PhD thesis Morphologie Mathématique, CMM- Centre de morphologie mathématique, ENSMP p.225.
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Abstract
In this thesis some color image analysis tools are presented aiming at extracting pertinent
information on the lighting conditions in which the picture was taken. Through these
tools, we seek to understand the semantic content of a picture by the way it is lit. This
knowledge is useful in several imaging domains such as augmented reality, motion picture
post-production, image indexation and pattern recognition.
Light's intrinsic information is not directly available in the digital image which is
the result of the integration and the digitalization of the incident spectral flux with the
scene's spectral reflectances. Thus, some semantic objects of interest according to our
problem are identified and the tools needed to analyze them are implemented. To do so,
physical lighting models are used in order to describe the light reflection behavior and to
understand how it modifies the image data.
Firstly, a photometric approach to the analysis of the lighting conditions is presented.
It is built around a shadow detection tool. The shadow information content allows the
measurement of a luminance contrast over the whole image, giving a ratio between the
energy of the direct light source and the ambient light source. In order to increase the
accuracy of the analysis, a sky detection tool is developed. It enables the extraction of
the meteorological conditions prevailing when the picture was taken. Indeed, the lighting
conditions vary greatly from a clear sky to a covered one.
Secondly, we present a method for detecting the illuminant's chrominance. This tool
takes advantage of the chromatic convergence which is based on the dichromatic model.
The convergence observed on non-homogeneous surfaces is used in order to identify the
illuminant's chrominance. The problems inherent to the existing techniques, related to the
statistical nature of the processing implemented, are bypassed by using the morphological
color segmentation. It allows segmenting the image in regions homogeneous in color and
luminance; each region being made of a single spectral re ectance. A filltering step is also
implemented in order to filter out the regions which do not verify the assumptions made
by the dichromatic model. Finally, the chromatic convergences computed on each region
are projected on the chromatic diagram. The most probable intersection of the set of all
straits with the locus of the planckian radiators is the point of convergence. This point
gives the coordinates of the illuminant's chrominance.
| Item Type: | PhD Thesis (PhD) |
|---|---|
| Thesis Supervisor: | Beucher, Serge |
| Date: | 17 December 2001 |
| Board of examiners: | Serra, Jean and Jourlin, Michel and Macq, Benoît and Guillemot, Christine and Touchard, Nicolas and Beucher, Serge |
| Discipline: | Morphologie Mathématique |
| Collection (Fonds): | ENSMP |
| Institution: | ENSMP |
| Department: | CMM- Centre de morphologie mathématique |
| Subjects: | 1. Mathematics and Applications |
| Uncontrolled Keywords: | Analyse image, éclairage, Image couleur, Ombre, Segmentation |
| ID Code: | 3315 |
| Deposited By: | Claudine Abauzit |
| Deposited On: | 30 January 2008 |
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