Books:

1. A.K.Jain, Fundamentals of Digital Image Processing, Prentice-Hall, 1989.
2. Rafael C. Gonzalez, Digital Image Processing, Second Ed., Pearson Education,2004.
3. Bernd Jahne , Digital Image Processing, 5th revised and extended edition,2002
4. Tinku Acharya, Image Processing Principles and Applications,2005

Online references:

1. http://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/OWENS/LECT14/lecture12.html
2. http://freevideolectures.com/Course/2316/Digital-Image-Processing-IIT-Kharagpur/26