Read support for subsampled RGB and YCbCr color channels was added in
4f4c3b34f8 and not documented at the time. Write support for YCbCr
appears to date to 61fb89ec54, the original commit.
Retain the existing language about YCbCr input conversion to RGB, even
though it's not completely correct. OpenJPEG through 2.5.0 doesn't set
color_space in opj_read_header(), so we end up in our
OPJ_CLRSPC_UNSPECIFIED fallback path, which guesses sRGB if there's no
component subsampling. This means we currently can't round-trip YCbCr via
JPEG 2000. The next OpenJPEG release will fix this, so leave the docs as
is.
Also fix typo: .j2p -> .jp2.
a72b5963d7