Hi Chris

I fully understand the desire to install the font on a PostScript
printer to keep the PS files smaller. To answer your question: I did not
ask for the business use case. The problem I'm struggling with in this
context is how to know about the CID meaning of the font, i.e. the
multi-byte encoding of the font.

When we do subsets in FOP, we re-index the glyphs starting with index 1
(or 3) by occurrence in the document. Only FOP knows which Unicode
character is represented by which CID. That's why we need the ToUnicode
CMap in PDF. Otherwise, text extraction would not be so easy.

In single-byte mode, the whole font is embedded (right now probably with
the same problems I've just fixed with rev1034094 for the TTF subset).
In this mode the Adobe character names map into the font, so 8-bit
encodings can be built to properly address the right characters even if
the font is not embedded. That's also how we currently do referenced TTF
fonts for PDF output.

If we fully embed the font as a CID font, we currently lose the
knowledge about which index represents which Unicode character.
Combining the font with a suitable CMap resolves the problem but at the
moment we only use Identity-H which is a 1:1 mapping. One solution would
be to turn the Unicode "cmap" table in the TrueType font into a custom PS
CMap and then use 16-bit Unicode characters directly. FOP currently
doesn't support that.

Also, if some PS platform allows to upload naked TrueType fonts, how
will they be represented in the PS VM? Are they CID fonts then or
single-byte fonts? If they are CID fonts, which CID system are they
following? I have no idea. The only way to be sure about this is by
installing a CID font plus CMap that is generated by FOP (which can be
done by extracting these resources from one of the PS streams. After
that, the font can be referenced, but it may not be portable to other
PS-generating applications.

And then, as Glen mentioned we have to have a strategy to deal with
glyphs with no representation in Unicode. I think I get where he goes
with that and it seems to be close to the CMap I mentioned above that is
derived from the Unicode "cmap" table in the TrueType font. At any rate,
FOP then has to learn to output Unicode characters (including private
area chars) instead of arbitrary CIDs coming from subsetting.

In the end, I'm not 100% I've understood all implications here. I hope
we'll get there soon. I guess a Wiki page would do us good here.

On 11.11.2010 17:50:46 Chris Bowditch wrote:
> Hi All,
> On 09/11/2010 14:43, Jeremias Maerki wrote:
> > On 09.11.2010 14:48:30 Vincent Hennebert wrote:
> >> There may be an interest in fully embedding a font for PostScript
> >> output. IIUC there may be a print manager that pre-processes PostScript
> >> files, extracts embedded fonts to store them somewhere and re-use them
> >> whenever needed. It can then strip the font off subsequent files and
> >> substantially lighten them, speeding up the printing process.
> > It makes the files smaller, but that will be the only thing that
> > improved printing performance. The PS interpreter still has to parse and
> > process the actual resource. It also needs to be noted that extracting
> > subset fonts doesn't make sense. I've already added the unique-ification
> > prefix to the TTF font names (like in PDF) to avoid problems like that.
> Yes I agree extracting subset fonts doesn't make sense, but extracting a 
> fully embedded font does have plenty of business applications. Which is 
> precisely why the introduction of a setting is required here. In some 
> cases it is important to bring the file size down; enter the subsetting 
> feature. Subsetting is particularly useful when creating print stream 
> with a relatively small number of pages, i.e. 100 or less and you have 
> large Unicode fonts to support Eastern character sets.
>   In other situations people using FOP want to be able to create large 
> Print streams to send to Print Bureaus. Print Bureaus tends to use 
> software to parse Print streams rather than sending them directly to a 
> printer. Those processes will often need to be able to process the 
> fonts, which they can only do if the full font is embedded rather than a 
> subset. As you already noted above, extracting a subset if useless.
> >> What’s the purpose of the ‘encoding’ parameter? It looks to me like
> >> users don’t care about what encoding is used in the PDF or PostScript
> >> file. All they want to have is properly printed documents that use their
> >> own fonts. I think that parameter should be removed in favour of Mehdi’s
> >> proposal, which IMO makes much more sense from a user perspective.
> > I don't know if it's necessary. That's why I wrote that maybe additional
> > research may be necessary. If we don't have it, we may have to build up
> > a /CIDMap that covers Unicode because there is otherwise no information
> > in the font which character indices correspond to which glyph as long as
> > we use /Registry (Adobe) /Ordering (Identity). Or: you configure a CID
> > map (encoding) that is tailored to the kind of document you want to
> > produce. The Unicode /CIDMap could result in rather big /CIDMap arrays
> > (65535 * 4 = 256KB) with lots of pointers to ".notdef".
>  From a user's perspective, the encoding parameter is too technical and 
> most user's ill not understand its purpose. If possible I would like to 
> reach a consenus on what we should do and then remove the parameter to 
> help cut down the complexity of configuring fonts. As you noted there 
> are now a bewildering number of options.
> > Before continuing with this there should be a broad understanding how
> > non-subset TrueType fonts shall be handled in PostScript (and PDF where
> > you can make the same case). Otherwise, a change like Mehdi proposed
> > doesn't improve anything.
> Are you asking what the business use case is for fully embedded fonts as 
> opposed to subset fonts. The ability to post process is the most 
> important use case. If the fonts are subset it become difficult to merge 
> Postscript files together or extract the font. Both are fairly common at 
> Print bureaus.
> >> Granted, there would be some redundancy with the referenced-fonts
> >> element. But is the additional flexibility of regexp really useful in
> >> the first place? I’m not too sure. Maybe that could be removed too.
> > I don't want that removed. I've been grateful for its existence more
> > than once. With the regexp I can make sure that, for example, all
> > variants of the "Frutiger" font are not embedded: Frutiger 45 Light,
> > Frutiger 55 Roman etc. etc.
> I concur the regexp stuff in the font referencing is useful. We can use 
> it to change the way whole font families are referenced without having 
> to list every font.
> > Anyway, I don't like constantly changing the way fonts are configured.
> > There's enough confusion with the way it's currently done already. I
> > won't veto a change like that but I'm not happy with it.
> I understand what you are saying there are a lot of options, but then 
> the requirements around fonts are complex so there is no escaping a 
> comlex configuration file.
> Thanks,
> Chris
> >> Vincent
> >>
> >>
> >> On 09/11/10 12:45, Jeremias Maerki wrote:
> >>> Hi Mehdi,
> >>> I'm against that since we already have mechanisms to control some of
> >>> these traits and this would overlap with them. For example, we have the
> >>> referenced-fonts element
> >>> (http://xmlgraphics.apache.org/fop/trunk/fonts.html#embedding)
> >>> which controls whether we embed or not. And we have the encoding-mode
> >>> attribute on the font element to control if single-byte or cid mode
> >>> should be used. Granted, that's not exactly what you're after, but I
> >>> believe this already covers 95% of the use cases if not more.
> >>>
> >>> The only thing you can't currently do is embed a full font in CID mode
> >>> (or reference it). The problem here is the character map that should be
> >>> used when in CID mode. I think that would require some research first so
> >>> we know how best to handle this. For example, referencing only makes
> >>> sense if a TrueType font can be installed directly on the printer. But
> >>> then, the question is in which mode the characters can be addressed.
> >>> Single-byte (like we currently fall back to) is probably not a problem
> >>> unless you need to print Asian documents. Please note that we also don't
> >>> support full TTF embedding/referencing in CID mode in PDF documents. So
> >>> I'm not sure if we really need that at the moment.
> >>>
> >>> If we do, I believe it would generally suffice to extend encoding-mode
> >>> from (auto|single-byte|cid) to (auto|single-byte|cid|cid-full). We may
> >>> need a "cmap" parameter then to change the default CMap (currently
> >>> "Identity-H" like in PDF) since our subsetting code uses custom mappings,
> >>> not Unicode or any other encoding scheme (like "90ms-RKSJ-H").
> >>>
> >>> On 09.11.2010 12:08:36 mehdi houshmand wrote:
> >>>> Hi,
> >>>>
> >>>> I'm working on making TTF subset embedding configurable such that a
> >>>> user can opt for either full font embedding, subset embedding or just
> >>>> referencing, this would be extending the work Jeremias submitted. I
> >>>> was considering adding a parameter to the font configuration file
> >>>> called "embedding" with 3 possible values "none", "subset" and "full".
> >>>> This would allow the user to configure the embedding mode on a font by
> >>>> font basis. What do people think about this proposal?
> >>>>
> >>>> Thanks
> >>>>
> >>>> Mehdi
> >>>
> >>>
> >>>
> >>> Jeremias Maerki
> >>>
> >
> >
> >
> > Jeremias Maerki
> >
> >
> >

Jeremias Maerki

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