Re: [pdf-devel] On predictor filters

[jemarch]

Hi JP.

   I am revisiting what the ISO says about predictors and found... that
   predictors are not considered by the PDF as a filter, they are an
   internal part of the LZWDecode and FlateDecode filters as stated in the
   7.4.4.3 section.

Right.

   I think that it is still usefull for correct decoupling that the
   predictors are implemented as a separate filter. Then, it is the
   pdf_stm_filter_install() function who must test for [LZW,Flate]Decode
   filters wheter they should be "predicted" first and create the predictor
   filter in that case.

   What do you think?

In my opinion it is the function _calling_ pdf_stm_filter_install who
should be aware of this issue, in the object layer. In the future we
may want to add a GNU extension providing new compression algorithms
that may get advantage of a highly predictable input, so we will want
pdf_stm_filter_install to install the specified "base filter", and
nothing more.