Image Processing Reference
Figure 13-6 Intra macroblocks changing to static macroblocks. Source: courtesy of Tektronix.
Earlier standards allowed macroblocks to be interpolated from two other frames. This is a
straightforward averaging. H.264 supports an adaptive weighting so a greater proportion
of the macroblock value is taken from one frame over the other.
Frame and Field Coding
The macroblock coding support for interlaced video is improved to allow pairing between
macroblocks in each field, which improves the handling of motion that takes place
between fields of the video sequence. This is provided as an adaptive technique, which is
switched on and off as required.
At the beginning of 2004, the most worrying issues facing potential adopters of the H.264
codec were the licensing of the MPEG-4 part 10 intellectual property rights and how the
revenues might be paid to the patent holders of any vital technologies.
Refer to Chapter 18 for a discussion about commercial issues, digital rights manage-
ment (DRM), and related topics.
Ongoing Development of the Standard
Some further work is now necessary because in strict encoding terms, part 10 is far better
than part 2. However, the technical capabilities of part 2 are more flexible than part 10.
There must be a merger of the two in order to render the older coding method com-
pletely obsolete. For the time being it may be necessary to code using part 2 if you want
to take advantage of some of the additional capabilities such as alpha channel-shape cod-
ing. In the fullness of time, it is very likely that part 10 will acquire all of these capabilities
but the working group must first incorporate the necessary changes into the standard.
That will take a little time.
As of 2004, the JVT team is reviewing what is needed and the standard may be
enhanced in due course to support alpha channels, shape coding, and some of the legacy
color models that earlier codecs supported.