R.J. Clarke

Image segmentation and motion-adaptive frame interpolation for coding moving sequences

The authors describe an approach to the coding of moving sequences that combines image segmentation with adaptive thresholding based on a priori knowledge about the scene and motion-adaptive frame interpolation techniques. In videoconference pictures the face is an area of high movement, and it is also the most noticeable part of the picture. Using such knowledge about the scene, the location of the face in alternate frames is determined, and a set of thresholds is chosen that allows segmentation of this part of the image more accurately than of the background. To achieve the high compression ratios required for transmission of videoconference and videophone pictures over the existing networks, only alternate frames are coded and transmitted. At the receiver a skipped frame k is produced by motion-adaptive interpolation of corresponding blocks of frames k-1 and k+1.<<ETX>>

An interpolative spatial domain technique for coding image sequences

The authors identify the main mechanism through which bits are consumed in the RBN (recursive binary nesting) coding scheme and determine ways in which this can be reduced. To this end, various forms of local motion-compensation are implemented and described, but the results are found to be disappointing. Different quantizers are then considered, but again the improvements were minimal. A scaled quantizer is introduced and shown to provide satisfactory performance. It is concluded that with the consequent increase in transmission efficiency for small block sample points, the use of RBN for quality coding of moving sequences at low channel rates is practicable.<<ETX>>

Video Compression Methods

The sections in this article are 1 Historical Note 2 Basic Techniques for Video Compression 3 Other Techniques for Video Data Compression 4 Advanced Techniques and Image Transmission

A new motion compensation/image sequence coding scheme

A general motion estimation algorithm using Fourier descriptors is developed, and results for a test sequence showing that the estimated 2-D motion parameters are very close to their values are given. A new image sequence coding scheme with combined motion compensation in which the above algorithm is implemented together with block matching is also proposed. A post-estimation technique is added to improve motion compensation efficiency. Mean/residue VQ is used further to encode the motion compensated error signals. A bit rate of 0.1 b/p is achieved for an 8 bit 256*256 moving sequence with good picture quality.<<ETX>>

Block testing in a variable resolution spatially interpolative moving image sequence coder

We have modified the interpolation and quad-tree based still picture Recursive Binary Nesting algorithm to code moving sequences. Central to the efficiency of this is the mechanism by which the extent of the quad-tree decomposition is controlled. Termed block testing this forms the subject of this paper.

Block classification image coding with combined transforms

Methods of employing a combination of two recently reported simple transforms (High Correlation Transform and Low Correlation Transform) using block adaptive transform coding with spatial domain activity classification are examined. It is found that for small block size, (viz. 8×8), increased coding efficiency can be had by employing a combination of the two new transforms, particularly for high activity images. The performance of such systems for small block size is found to be close, and sometimes superior, to that of a more conventional block classification adaptive transform coder employing the more complex real number cosine transform.