COST 211 ter role in the initial phase of H.263 development in ITU

COST 211 bis had been very active in the development of the video compression standard H.261. The technical work on this standard was finished around 1987. In 1990/91 the simulation group of COST 211 ter initiated work towards improved compression at even lower bitrates than was foreseen for H.261. The bitrates under considerations - (8-32) kb/s - were in line with bitrates available over modems on PSTN lines at that time. The picture format under consideration was QCIF (the smallest picture format defined in H.261). Some of the main improvements from H.261 may be summarised as:

• Use of halfpixel motion prediction instead of the loopfilter defined in H.261. This technique had already been adopted by MPEG at that time.
• Reduced load of overhead bits in order to be able to reach the very low bitrates (8 kb/s).
• Introduction of an improved Variable Length Code (VLC) table for more efficient coding of transform coefficients.

Simulation models (SIMx) were developed. In 1992 ITU started an activity for development of videocompression to be used over telephone modems. The goals were similar to those of COST 211 ter. Therefore the simulation model SIM3 was proposed and accepted as the starting point of the work in ITU towards H.263. If we take a look at the resulting H.263 standard, the basic version (without options) is very similar to SIM3.

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