theora - Oct 2009 - [1.1.1] Too much quantization on flat red surfaces

Hi,

I've tested Theora on an HD-ready material, with quality 7, single pass.
Resulting bitrate was 1.8Mb/s. Most parts of a movie encoded this way look
fine, usually better than a DVD, and in daylight scenes, have no noticeable
artifacts at all. But it seems that red surfaces are too much compressed;
blocking artifacts are clearly visible on them. Also, white people have
slightly smeared faces, especially in scenes with low motion.

I guess I could pass a custom quantization matrix to
th_encode_ctl<file:///home/wojownik/Pulpit/libtheora-1.1.1/doc/libtheora/html/group__encfuncs.html#g3a427f6514dfdc01ea72172c469d51d9>()
but I got no idea how to affect only the red plane while leaving the
rest
of encoding as it is. So please tell me how to deal with it.
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