Currently, openjpeg v1.3 has a very limited implementation of ROI. The
only thing that can be done is upshift a whole component (as there is
no spatial zone selection, i wonder if we can even call this ROI ...).
However, this gives a basis to go one step further and implement a
true ROI option.
The JPEG 2000 ROI feature is described in annex H of the standard.
There are basically two things to implement :
* The mask generation : based on coordinates provided by the user, a
binary mask has to be generated for each subband (or even for each
code-block if we want to get the finest granularity when specifying
the ROI). I would say that this should be done when doing the DWT
(=>dwt_encode(_real) in dwt.c) but I should maybe investigate this a
* The scaling operation : based on the mask, some coefficients have to
be up-scaled in order to be encoded first during entropy coding
(Maxshift method). This should surely be done in t1.c
(t1_encode_cblk), before applying the three coding passes. Depending
on the granularity required by the ROI implementation, the whole code-
block will be up-shifted or only some of its coefficients (the one
selected by the binary mask).
Well, writing this, i realize that it's not so easy to do... Let us
know if you investigate this a bit further or feel free to ask for
more details (not sure i will be able to answer though).
Le 02-mars-08 à 16:23, James a écrit :
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