Bellers E.B., de Haan G. De-interlacing. A Key Technology for Scan Rate Conversion

Elsevier, 2000. — 369 p.The human visual system is less sensitive to flickering details than to large-area flicker. Television displays apply interlacing to profit from this fact, while broadcast formats were originally denned to match the display scanning format. As a consequence, interlace is found throughout the video chain. If we describe interlacing as a form of spatio-temporal subsampling, then de-interlacing, the topic of our book, is the reverse operation aiming at the removal of the sub-sampling artefacts.
The major flaw of interlace is that it complicates many image processing tasks. Particularly, it complicates scanning-format conversions. These were necessary in the past mainly for international programme exchange, but with the advent of high-definition television, videophone, Internet, and video on PCs, many scanning formats have been added to the broadcast formats, and the need for conversion between formats is increasing.
This increasing need, not only in professional but also in consumer equipment, has restarted the discussion 'to interlace or not to interlace'. Particularly, this issue divides the TV and the PC communities. The latter seems biased towards the opinion that present-day technologies are powerful enough to produce progressively scanned video at high rate and do not need to trade-off vertical against time resolution through interlacing. On the other hand, the TV world seems more conservative, and biased towards the opinion that present day technologies are powerful enough to adequately de-interlace video material, which reduces, or even eliminates, the need to introduce incompatible standards and sacrifice the investments of so many consumers.
It appears that the two camps have had disjunct expertises for a long time. In a world where the two fields are expected by many to be converging, it becomes inevitable to appreciate and understand each other's techniques to some extent. Currently, the knowledge in the PC community on scan rate conversion in general, and on de-interlacing in particular, seems to be lagging behind on the expertise available in the TV world. Given the availablility of advanced motion-compensated scan rate conversion techniques in consumer TV-sets since some years, it is remarkable that the PC community still relies on techniques developed for use in the television chain in the seventies.
The question, 'to interlace or not to interlace', touches various issues. Whether present-day technologies are powerful enough to produce progressively scanned video at a high rate and a good signal to noise ratio is not evident. Moreover, a visual-communication system also involves display and transmission of video signals. The issue translates for the transmission channel into the question: 'Is interlacing and de-interlacing still the optimal algorithm for reducing the signal bandwidth with a factor of two?' Before answering this question, it is necessary to know what can be achieved with de-interlacing techniques nowadays. Although the literature provides evidence that an all-progressive chain gives at least as good an image quality as an all-interlaced chain with the same channel bandwidth, recent research suggests that modern motion-compensated de-interlacing techniques, used in todays consumer electronics products can improve the efficiency of even highly efficient compression techniques. It seems appropriate, therefore, to evaluate the available options in de-interlacing, before jumping to conclusions.Part I Basic technology
Overview of de-interlacing algorithms
Overview on motion estimation techniques
Part II System optimization
Accurate motion estimates from interlaced video
On the optimization of de-interlacing
Part III The future of interlace
The efficiency of interlaced versus progressive video on an MPEG-2 digital channel
Towards an optimal display format
ConclusionsA: Cycles per degree and cycles per picture width
B: Motion and alias
C: Interpolation for sub-pixel de-interlacing
D: Example: derivation of a 4 taps TGST filter
E: Robustness of the TGST de-interlacer
F: MS de-interlacer optimization for a programmable architecture