Of course, compression can also be indicated at the HTTP layer with the
"content-coding" header. IANA maintains a registry of content-coding value
Sent by: firstname.lastname@example.org
I agree that these are commonly used within TIFF and you are correct that
they are not really required to support IPPFAX. However, the compression
methods can be used independently from TIFF and that is the situation that
need to cover. We do have products that support some of these compression
methods and I believe that they should be all registered for use with IPP.
I would like to reopen this issue as a proposal to register these keywords
for the IPP compression attribute.
Sorry you were unable to attend the meeting.
We did discuss your suggestion to add a bunch of keywords to the IPP
"compression" and "compression-supported" attributes for MR, MH, MMR, etc.
We decided that the "compression" IPP operation attribute is referring to
the compressions of the overall print data stream, not the encoding methods
within a document format that are used to reduce the size. We think that
your list are all examples used within TIFF-FX and so should not be
used in the "compressions" IPP operation attribute. In fact, if a sender
were to encode a TIFF-FX file using one of these encodings, the file would
actually grow larger, since the encoding had already been applied
An IPPFAX client can determine which encodings are used (MR, MH, MMR, etc.)
for the image/tiffx MIME type by querying the Printer's
"ippfax-uif-profiles-supported". Each profile requires certain encodings.
If an implementation uses additional encodings above the REQUIRED ones for
profile, then it MUST indicate them in the CONNEG string value of the
Printer's "ippfax-uif-profile-capabilities" attribute, so that the client
can discover them.
For support of IPP FAX, the attributes "compression" and
"compression-supported" must have the following new keywords defined:
1. mh (modified Huffman)
2. mr (modified READ)
3. mmr (modified modified READ)
4. jpeg (Joint Photographic Experts Group)
5. jbig-lossless-bw (Joint Bi-level Image Group, black and white)
I am not sure if this covers all the possibilities. I propose that this be
a discussion topic next week.
My travel request was not approved, so if you could lead this discussion, I
would appreciate it.
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