References 325 Similarly to the case for a random sequence, we can define mean, correlation, and covariance functions for a random process. The concept of stationarity for random process is analogous to that of random sequences. Stationary random processes have power spectral densities that are the Fourier transforms of their stationary correlation functions. There are also sampling theorems that apply for bandlimited stationary random processes. Much more information on random sequences and processes can be found in textbooks such as [1]. REFERENCES [1] H. Stark and J. W. Woods, Probability and Random Processes with Appl. to Signal Process., 3rd Ed., Prentice-Hall, EnglewoodCliffs, NJ, 2002. [2] J. R. Jain and A. K. Jain, "Displacement Measurement and Its Application in Interframe Image Coding," IEEE Trans. Comm., vol. COM-29, pp. 1799­1804, December 1981. [3] B. Girod, "The Efficiency of Motion-Compensating Prediction for Hybrid Coding of Video Sequences," IEEE J. Select. Areas in Comm., vol. SAC-5, pp. 1140­1154, August 1987. [4] J. Lim, Two-Dimensional Signal and Image Processing, Prentice-Hall, EnglewoodCliffs,