mirror of https://github.com/qpdf/qpdf.git
Clarify documentation of advanced parsing options
This commit is contained in:
Jay Berkenbilt
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2017-12-25 Jay Berkenbilt <ejb@ql.org>
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* Clarify documentation around options that control parsing but
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not output creation. Two options: --suppress-recovery and
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--ignore-xref-streams, were documented in the "Advanced
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Transformation Options" section of the manual and --help output
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even though they are not related to output. These are now
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described in a separate section called "Advanced Parsing Options."
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* Implement remaining PNG filters for decode. Prior versions could
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decode only the "up" filter. Now all PNG filters (sub, up,
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average, Paeth, optimal) are supported for decoding. Thanks to
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@ -865,6 +865,56 @@ outfile.pdf</option>
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to be bothered with.
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</para>
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</sect1>
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<sect1 id="ref.advanced-parsing">
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<title>Advanced Parsing Options</title>
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<para>
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These options control aspects of how qpdf reads PDF files. Mostly
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these are of use to people who are working with damaged files.
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There is little reason to use these options unless you are trying
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to solve specific problems. The following options are available:
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<variablelist>
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<varlistentry>
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<term><option>--suppress-recovery</option></term>
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<listitem>
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<para>
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Prevents qpdf from attempting to recover damaged files.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--ignore-xref-streams</option></term>
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<listitem>
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<para>
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Tells qpdf to ignore any cross-reference streams.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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<para>
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Ordinarily, qpdf will attempt to recover from certain types of
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errors in PDF files. These include errors in the cross-reference
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table, certain types of object numbering errors, and certain types
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of stream length errors. Sometimes, qpdf may think it has
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recovered but may not have actually recovered, so care should be
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taken when using this option as some data loss is possible. The
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<option>--suppress-recovery</option> option will prevent qpdf from
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attempting recovery. In this case, it will fail on the first
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error that it encounters.
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</para>
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<para>
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Ordinarily, qpdf reads cross-reference streams when they are
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present in a PDF file. If <option>--ignore-xref-streams</option>
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is specified, qpdf will ignore any cross-reference streams for
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hybrid PDF files. The purpose of hybrid files is to make some
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content available to viewers that are not aware of cross-reference
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streams. It is almost never desirable to ignore them. The only
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time when you might want to use this feature is if you are testing
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creation of hybrid PDF files and wish to see how a PDF consumer
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that doesn't understand object and cross-reference streams would
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interpret such a file.
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</para>
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</sect1>
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<sect1 id="ref.advanced-transformation">
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<title>Advanced Transformation Options</title>
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<para>
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@ -975,14 +1025,6 @@ outfile.pdf</option>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--suppress-recovery</option></term>
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<listitem>
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<para>
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Prevents qpdf from attempting to recover damaged files.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--object-streams=<replaceable>mode</replaceable></option></term>
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<listitem>
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@ -1012,14 +1054,6 @@ outfile.pdf</option>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--ignore-xref-streams</option></term>
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<listitem>
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<para>
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Tells qpdf to ignore any cross-reference streams.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--preserve-unreferenced</option></term>
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<listitem>
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@ -1142,17 +1176,6 @@ outfile.pdf</option>
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who wish to study PDF content streams or to debug PDF content.
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You should not use this for “production” PDF files.
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</para>
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<para>
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Ordinarily, qpdf will attempt to recover from certain types of
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errors in PDF files. These include errors in the cross-reference
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table, certain types of object numbering errors, and certain types
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of stream length errors. Sometimes, qpdf may think it has
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recovered but may not have actually recovered, so care should be
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taken when using this option as some data loss is possible. The
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<option>--suppress-recovery</option> option will prevent qpdf from
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attempting recovery. In this case, it will fail on the first
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error that it encounters.
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</para>
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<para>
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Object streams, also known as compressed objects, were introduced
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into the PDF specification at version 1.5, corresponding to
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@ -1177,18 +1200,6 @@ outfile.pdf</option>
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qpdf will also make sure the PDF version number in the header is
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at least 1.5.
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</para>
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<para>
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Ordinarily, qpdf reads cross-reference streams when they are
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present in a PDF file. If <option>--ignore-xref-streams</option>
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is specified, qpdf will ignore any cross-reference streams for
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hybrid PDF files. The purpose of hybrid files is to make some
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content available to viewers that are not aware of cross-reference
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streams. It is almost never desirable to ignore them. The only
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time when you might want to use this feature is if you are testing
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creation of hybrid PDF files and wish to see how a PDF consumer
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that doesn't understand object and cross-reference streams would
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interpret such a file.
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</para>
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<para>
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The <option>--qdf</option> flag turns on QDF mode, which changes
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some of the defaults described above. Specifically, in QDF mode,
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13
qpdf/qpdf.cc
13
qpdf/qpdf.cc
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@ -355,6 +355,17 @@ valid file name and not a valid range.\n\
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See the manual for examples and a discussion of additional subtleties.\n\
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\n\
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\n\
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Advanced Parsing Options\n\
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-------------------------------\n\
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\n\
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These options control aspects of how qpdf reads PDF files. Mostly these are\n\
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of use to people who are working with damaged files. There is little reason\n\
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to use these options unless you are trying to solve specific problems.\n\
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\n\
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--suppress-recovery prevents qpdf from attempting to recover damaged files\n\
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--ignore-xref-streams tells qpdf to ignore any cross-reference streams\n\
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\n\
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\n\
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Advanced Transformation Options\n\
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-------------------------------\n\
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\n\
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@ -366,9 +377,7 @@ familiar with the PDF file format or who are PDF developers.\n\
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--compress-streams=[yn] controls whether to compress streams on output\n\
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--decode-level=option controls how to filter streams from the input\n\
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--normalize-content=[yn] enables or disables normalization of content streams\n\
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--suppress-recovery prevents qpdf from attempting to recover damaged files\n\
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--object-streams=mode controls handing of object streams\n\
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--ignore-xref-streams tells qpdf to ignore any cross-reference streams\n\
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--preserve-unreferenced preserve unreferenced objects\n\
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--newline-before-endstream always put a newline before endstream\n\
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--qdf turns on \"QDF mode\" (below)\n\
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