[pdf-devel] Filter parameters

[jemarch]

Just a note for the hackers writing a filter implementation:

When writing a filter implementation please keep in mind that we
should always use the parameter names specified by the PDF 1.7
specification. The parameter names are documented in the "Syntax"
chapter, and are used as keys in the filter dictionary.

So, for example, the LZW filters should use the following parameter
names in the pdf_hash:

     "Predictor" (interpreted as an integer)
     "Colors" (interpreted as an integer)
     "BitsPerComponent" (interpreted as an integer)
     "Columns" (interpreted as an integer)
     "EarlyChange" (interpreted as an integer)

This will ease the task in the near future, since we are going to
implement the pdf_dict_t object in top of a pdf_hash_t object, in the
object layer.