טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentEfim Koreban
SubjectGeometry by Deflaring
DepartmentDepartment of Electrical Engineering
Supervisor Full Professor Schechner Yoav
Full Thesis textFull thesis text - English Version


Abstract

Image irradiance may not represent well the object radiance at the corresponding location. One reason is that part of the light emanating from the scene undergoes reflections between components in the lens system, becoming stray light. This light affects unintended locations in the image plane, thus biasing the intensity readout in these locations. This phenomenon is especially noticed when there is a very bright light source in or near the field of view. This is known as lens flare or veiling glare. The glare type called aperture ghosting appears as additive light in the shape of the lens aperture. This thesis analyses this glare type and creates geometric and photometric models of the phenomenon. Then, we propose a simple method or removing (and thus recovering) this flare. Finally, we use the recovered flare to estimate the projection of the position of the optical center of the camera and of the location of the illumination source.

The geometric model shows that flare spots lie on a straight line that crosses the projections of the light source and the optical center (OC) of the camera. When we move the camera, the OC moves as well, and the flare covers different parts of the image. When we take a series of images, every object appears without the flare at least in one image. Hence we can remove the non-negative flare by applying a minimum operator on the registered images.

Once the flare is removed and extracted, we use it in the global coordinate system (after registration) to recover the illumination source location. We also use it in local coordinate system, to recover the OC of the camera. We propose a simple method that analyzes the flare images in the Radon domain, and extracts the wanted locations using only low-level calculations.