Little is gained from the return type checks, it mostly serves to
clutter the code.

Rather than coding all syntax elements for both transform types
irrespective of the in-use type, this commit codes only those that
are necessary for a given transform type.

Philip A. Chou authored Apr 03, 2018 and David Flynn committed Jun 05, 2018

This commit introduces the rahtLeafDecimationDepth parameter to allow
chroma sub-sampling by decimating the coefficients in the bottom n
levels of the tree.

The default value of 3 provides chroma sub-sampling by a factor of 2
in each dimension.

Philip A. Chou authored Mar 25, 2018 and David Flynn committed Jun 05, 2018

This commit ports the Region Adaptive Hierarchical Transform for
attribute coding with colour and reflectance variants.

Khaled Mammou authored Mar 25, 2018 and David Flynn committed Jun 05, 2018

This commit reorganises the attribute coders to allow integration
of the RAHT variant.

In order to support multiple different attribute compression schemes,
this commit moves the existing attribute compression code into a
self-contained class.