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rework outputintent interface, unfinished! needs testing
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Ulrike Fischer committed Feb 18, 2021
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196 changes: 184 additions & 12 deletions l3pdfmeta.dtx
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% |/A| dictionary of an action. The check should supply the user
% subtype without slash e.g. as |GoTo| (pass) or |Movie| (failure).
% \end{description}
%
% \subsection{Colorprofiles and OutputIntent}
%
% The pdf/A standards require that a color profile is embedded and
% referenced in the catalog in the |/OutputIntent| array.
%
% The problem is that the pdf/A standards also require, that if the PDF has more then
% one entry in the |/OutputIntent| array (which is allowed), their /DestOutputProfile
% should all reference the same color profile\footnote{see rule 6.2.2-2 at
% \url{https://docs.verapdf.org/validation/pdfa-part1/}}.
%
% Enforcing this fully is impossible as it is difficult to inspect
% and remove entries from the |/OutputIntent| added manually by users or packages with
% |\pdfmanagement_add:nnn {Catalog}{OutputIntents}{|\meta{object reference}|}|.
%
% So we provide a dedicated interface to avoid the need of manual
% user settings and allow the code to handle the requirements of the standard.
%
% The interface has to handle the following points:
% \begin{itemize}
% \item We have to assume that some documents wants to add more than one OutputIntent with
% varying subtypes.
% \item While currently only |/GTS_PDFA1| and |/GTS_PDFX| seem to
% be relevant, we have to assume that the list of subtypes is open.
% \item But we can imho assume that every subtype is there at most once.
% \item The referenced color profile can be used also other means, e.g. an /ICCBased
% color space. We must avoid that it is embedded twice in this case.
% \item While we can predeclare some standard icc-profiles, an interface to
% setup more is needed.
% \end{itemize}
%
% The interface looks like this
%
% \begin{verbatim}
% \DeclareDocumentMetadata
% {
% %other options
% colorprofiles=
% {
% A = sRGB.icc, %or a or longer GTS_PDFA1 = sRGB.icc
% X = FOGRA39L_coated.icc, % or x or longer GTS_PDFX
% ISO_PDFE1 = whatever.icc
% }
%
% }
% \end{verbatim}
%
% |sRGB.icc| and |FOGRA39L_coated.icc| (from the \pkg{colorprofiles} package
% are predefined and will work directly. |whatever.icc| will need special setup in
% the document preamble (how exactly will be decided later).
%
% If a standard is detected or set which requires
% that all |/DestOutputProfile| reference the same
% color profile, the setting is changed to the equivalent of
%
% \begin{verbatim}
% \DeclareDocumentMetadata
% {
% %other options
% colorprofiles=
% {
% A = sRGB.icc, %or longer GTS_PDFA1 = sRGB.icc
% X = sRGB.icc,
% ISO_PDFE1 = sRGB.icc
% }
%
% }
% \end{verbatim}
%
% The pdf/A standards will use |A=sRGB.icc| by default, so this doesn't
% need to be declared explicitly.
%
%
% \end{documentation}
%
% \begin{implementation}
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%===============
% to be continued https://docs.verapdf.org/validation/pdfa-part1/
% - Outputintent/colorprofiles requirements
% an outputintent should be loaded. There are more requirements
% but these are not tested
,outputintent =
,outputintent_subtype = {GTS_PDFA1}
,outputintent_profile = {sRGB.icc}
% an outputintent should be loaded.
,outputintent =
% its subtype:
,outputintent_subtype = {GTS_PDFA1}
% only one (A) profile
,outputintent_unique =
% - no Alternates key in image dictionaries
% - no OPI, Ref, Subtype2 with PS key in xobjects
% - Interpolate = false in images
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% and an outputintent need for PDF/A for now. There will be need to extend it later,
% so we try for enough generality.
%
% Adding a profile and an intent is technically easy:
% \begin{enumerate}
% \item Embed the profile as stream with
% \begin{verbatim}
% \pdf_object_unnamed_write:nn{fstream} {{/N~4}{XXX.icc}}
% \end{verbatim}
% \item Write a |/OutputIntent| dictionary for this
% \begin{verbatim}
% \pdf_object_unnamed_write:nx {dict}
% {
% /Type /OutputIntent
% /S /GTS_PDFA1 % or GTS_PDFX or ISO_PDFE1 or ...
% /DestOutputProfile \pdf_object_ref_last: % ref the color profile
% /OutputConditionIdentifier ...
% ... %more info
% }
% \end{verbatim}
% \item Reference the dictionary in the catalog:
% \begin{verbatim}
% \pdfmanagement_add:nnx {Catalog}{OutputIntents}{\pdf_object_ref_last:}
% \end{verbatim}
%
% But we need to do a bit more work, to get the interface right.
% The object for the profile should be named, to allow l3color to reuse it
% if needed. And we need container to store the profiles, to handle the
% standard requirements.
%
% \begin{variable}{\g_@@_outputintents_prop}
% This variable will hold the profiles for the subtypes. We assume
% that every subtype has only only color profile.
% \begin{macrocode}
\prop_new:N \g_@@_outputintents_prop
% \end{macrocode}
% \end{variable}
% Some keys to fill the property.
% \begin{macrocode}
\keys_define:nn { document / metadata }
{
colorprofiles .code:n =
{
\keys_set:nn { document / metadata / colorprofiles }{#1}
}
}
\keys_define:nn { document / metadata / colorprofiles }
{
,A .code:n =
{
\prop_gput:Nnn \g_@@_outputintents_prop
{ GTS_PDFA1 } {#1}
}
,a .code:n =
{
\prop_gput:Nnn \g_@@_outputintents_prop
{ GTS_PDFA1 } {#1}
}
X .code:n =
{
\prop_gput:Nnn \g_@@_outputintents_prop
{ GTS_PDFX } {#1}
}
x .code:n =
{
\prop_gput:Nnn \g_@@_outputintents_prop
{ GTS_PDFX } {#1}
}
unknown .code:n =
{
\prop_gput:Nxn \g_@@_outputintents_prop
{ \l_keys_key_str } {#1}
}
}
% \end{macrocode}
% \begin{macrocode}
\pdfdict_new:n {l_pdfmeta/outputintent}
\pdfdict_put:nnn {l_pdfmeta/outputintent}
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\AddToHook{begindocument/end}
{
\prop_if_in:NnT\g_@@_standard_prop {outputintent}
\pdfmeta_standard_verify:nF {outputintent}
{
\exp_args:NNx
\prop_if_in:NnF \g_@@_outputintents_prop
{
\pdfmeta_standard_item:n {outputintent_subtype}
}
{
\prop_gput:Nxn { \pdfmeta_standard_item:n {outputintent_subtype} }{sRGB.icc}
}
}
\pdfmeta_standard_verify:nTF {outputintent_unique}
{
\prop_map_inline:Nn \g_@@_outputintents_prop
{
\exp_args:Nx
\@@_embed_colorprofile:n
{\prop_item:Nn \g_@@_outputintents_prop {#2}}
\exp_args:Nxx
\@@_write_outputintent:nn
{#2}
{#1}
}
}
{
\exp_args:Nx
\@@_embed_colorprofile:n
{\prop_item:Nn \g_@@_standard_prop {outputintent_profile}}
\exp_args:Nxx
\@@_write_outputintent:nn
{\prop_item:Nn \g_@@_standard_prop {outputintent_profile}}
{\prop_item:Nn \g_@@_standard_prop {outputintent_subtype}}
\@@_embed_colorprofile:n
{\prop_item:Nn \g_@@_outputintents_prop {GTS_PDFA1}}
\prop_map_inline:Nn \g_@@_outputintents_prop
{
\exp_args:Nxx
\@@_write_outputintent:nn
{#2}
{GTS_PDFA1}
}
}
}
% \end{macrocode}
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