Hybrid mapping parameter estimation using hierarchical structure in object-oriented coding

This paper investigates motion estimation and compensation in object-oriented analysis-synthesis coding. Object-oriented coding employs a mapping parameter technique for estimating motion information in each object. The mapping parameter technique using gradient operators requires high computational complexity. The main objective of this paper is to propose a hybrid mapping parameter estimation method using the hierarchical structure in object-oriented coding. The hierarchical structure employed constructs a low-resolution image. Then six mapping parameters for each object are estimated from the low-resolution image and these parameter values are verified based on the displaced frame difference (DFD). If the verification test succeeds, the parameters and object boundaries are coded. Otherwise, eight mapping parameters are estimated in a low-resolution image and the verification test is again applied to an image reconstructed by estimated parameters. If it succeeds, the parameters and object boundaries are coded, otherwise, the regions are coded by second-order polynomial approximation. Theoretical analysis and computer simulation show that the peak signal to noise ratio (PSNR) of the image reconstructed by the proposed method lies between those of images reconstructed by the conventional 6- and 8-parameter estimation methods with reduction of the computation time by a factor of about four.