This allows losslessly transposed or rotated 4:1:1 JPEG images to be
losslessly cropped, partially decompressed, or decompressed to planar
YUV images.
Because tj3Transform() allows multiple lossless transformations to be
chained together, all subsampling options need to have a corresponding
transposed subsampling option. (This is why 4:4:0 was originally
implemented as well.) Otherwise, the documentation would be technically
incorrect. It says that images with unknown subsampling types cannot be
losslessly cropped, partially decompressed, or decompressed to planar
YUV images, but it doesn't say anything about images with known
subsampling types whose subsampling type becomes unknown if the image is
rotated or transposed. This is one of those situations in which it is
easier to implement a feature that works around the problem than to
document the problem.
Closes#659
fc881ebb21