Dibakar Raj Pant will defend his PhD thesis
Dibakar Raj Pant has submitted his academic thesis as part of the doctoral work at The Doctoral School ED SIS 488, of the University Jean Monnet, Saint Etienne, France. The thesis has been conducted at The Norwegian Color Research Laboratory, Gjøvik University College (GUC).
Title of the thesis: “Line Element and Variational Methods for Color Difference Metrics”
Public defense of the thesis: On Friday February 17th 2012 at 13.00 in Auditorium Eureka at Gjøvik University College. Dibakar Raj Pant defends his thesis for the degree of Doctor of Philosophy in Images, Vision and Signal.
Jury/Evaluation Committee
• Reviewer/opponent: Professor Manuel Melgosa, Department of Optics, University of Granada, Spain
• Reviewer/opponent: Professor Christine Fernandez-Maloigne Laboratoire XLIM-SIC: signal - image – communications, Département de l'Institut XLIM, University of Poitiers, France
• Jury member: Professor Rune Hjelsvold, The Media Technology Laboratory, Department of Computer Science and Media Technology, Gjøvik University College
•Jury member: Professor Jon Yngve Hardeberg, The Norwegian Color Research Laboratory &The Media Technology Laboratory, Department of Computer Science and Media Technology, Gjøvik University College
• Principal supervisor: Professor Alain Tremeau, the Laboratoire Hubert Curien, Université Jean Monnet, Saint-Etienne, France
• Co-supervisor: Associate Professor Ivar Farup, The Norwegian Color Research Laboratory & The Media Technology Laboratory, Department of Computer Science and Media Technology, Gjøvik University College.
Information about the Ph.D.-Candidate Dibakar Raj Pant
Dibakar Raj Pant received his M.Sc. in Computer Science/Signal processing from the University of Joensuu, Finland in 2006 and a B.Sc. in Electrical and Electronic Engineering from Bangladesh Institute of Technology. During his Masters studies, he worked as a trainee researcher in the Infotnonics Center, Color Research Laboratory, the University of Joensuu. He has also several years of teaching experience as well as industry work experience as an electrical engineer. In 2009, he started his PhD in Color Difference metric at the Norwegian Color Research Laboratory, Gjøvik University College under the supervision of Prof. A. Tremeau, University of Jean Monnet, France and Ass. Prof. I. Farup, Gjøvik University College, Gjøvik.
Abstract of the Ph.D.-dissertation
For precision color matching, visual sensitivity to small color difference is an essential factor. Small color differences can be measured by the just noticeable difference (JND) ellipses which represent the color discrimination ability of the human visual system. Mathematically, such an ellipse can be described by a positive definite quadratic differential form, which is also known as the Riemannian metric. The Riemannian metric can be used as a tool to study the performance of various color spaces and color difference metrics for measuring the perceptual color differences. It also computes the shortest distance between any two points in a color space. The shortest distance is called a geodesic. According to Schrodinger's hypothesis geodesics starting from the neutral point of a surface of constant brightness correspond to the curves of constant hue. The chroma contours are closed curves at constant intervals from the origin measured as the distance along the constant hue geodesics. This hypothesis can be utilized to test the performance of color difference formulas to predict perceptual attributes (hue and chroma) and distribution of color stimulus in any color space. In this research work, a method to formulate line element models of color difference formulas the Delta E*ab, the Delta E*uv, the OSA-UCS Delta E_E and infinitesimal approximation of CIEDE2000 is presented. The performance of these four color difference formulas is evaluated by comparing computed ellipses with experimentally observed ellipses in different chromaticity diagrams. With the Riemannian metrics of above four formulas, Schrodinger's hypothesis is tested by computing hue geodesics and chroma contours of these metrics in the CIELAB color space and compared with the Munsell system. It is found that no color difference formulas predict precisely the visual color difference. The latest color difference formulas like the OSA-UCS Delta E_E and infinitesimal approximation of CIEDE2000 do not show better performance to predict hue geodesics and chroma contours than the conventional CIELAB and CIELUV color space based formulas with respect to the Munsell color order system.
Picture by Brynjar Eidstuen
