Project: Color Image Filtering

PEOPLE

Canhui Cai, Luca Lucchese, S.K.Mitra

OBJECTIVE

Two specific problems were considered under this project.  The first problem was on the accurate determination of edges in a color image based on a quaternion rep­resentation, while the second problem was filtering of color images based the Center of Gravity Law of Color Mixture . 

A quaternion number is a generalization of the con­ventional complex number.  It consists of a real part and three imaginary parts.  An RGB color image can be rep­resented by a quaternion sys­tem of pixels in which the three imaginary parts represent the red, green, and the blue components, while the real part is set to zero.  A normalized color difference edge detector has been devel­oped based on this new type of rep­resentation.  The edge detector generates edges only where sharp changes of color occur in the origi­nal color image.  Experimental re­sults have verified the improved performance of the new edge detector compared to some well-known methods.  A paper describing the new edge detector along with the ex­per­imental results was presented at an international conference [1].

We have developed a new approach to color filtering which operates on the representation of an im­age in the xyY color space.  In this color space the chromatic in­formation is carried by the CIE chromatic coordinates, x and y , and the in­tensity informa­tion by the CIE tristimulus value Y .  The particular struc­ture of its xy chromatic subspace requires one to add colors in compliance with the Center of Gravity Law of Color Mixture .  Our origi­nal contribution consists in de­riving from this law a simple color filtering scheme, nonlinear in the x and y components, and linear in Y , which preserves the convexity of the chromatic informa­tion.  This impor­tant property has been demon­strated by a number of practical filtering examples.  A paper con­taining the initial results was presented at an international conference [2].

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