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    1 .TH PDFIDIFF 1 "2021 Jan 15" littleutils
    2 .SH NAME
    3 pdfidiff \- compares two PDF files and write differences to a third file
    4 file.
    5 .SH SYNOPSIS
    6 \fBpdfidiff\fR
    7 [\fB\-h(elp)\fR]
    8 [\fB\-f\fR\~\fIfuzz_dist\fR]
    9 [\fB\-g(hostscript)\fR]
   10 [\fB\-m\fR\~\fImode\fR]
   11 [\fB\-o(ptimize)\fR]
   12 [\fB\-q(uiet)\fR]
   13 [\fB\-r\fR\~\fIresolution\fR]
   14 [\fB\-s(ingle_threaded)\fR]
   15 \fIoldfile newfile deltafile\fR
   16 .SH DESCRIPTION
   17 \fBpdfidiff\fR reads in any two PDF files readable by \fBghostscript\fR and
   18 write out an image-based "delta" file that represents the differences between
   19 the two files.
   20 .SH OPTIONS
   21 .TP
   22 \fB\-h\fR
   23 Print help and quit.
   24 .TP
   25 \fB\-g\fR
   26 Use ghostscript (\fBgs\fR) instead of poppler (\fBpdftocairo\fR) as the PDF
   27 rendering engine.
   28 .TP
   29 \fB\-f\fR\~\fIfuzz_dist\fR
   30 When performing a grayscale difference analysis, any pixel values within the
   31 distance specified by \fB\-f\fR option are considered equal.  This option has
   32 no effect on a color difference analysis.  The default value is\~\fI1\fR.
   33 .TP
   34 \fB\-m\fR\~\fImode\fR
   35 Set of the mode of the difference analysis.  At present, five modes are
   36 available, as described in the MODES section.  The default mode is\~\fI2\fR.
   37 .TP
   38 \fB\-q\fR
   39 Cause \fBpdfidiff\fR to silence the progress information normally printed
   40 during operation.
   41 .TP
   42 \fB\-r\fR\~\fIresolution\fR
   43 Use the specified resolution (in DPI) when converting from PDF to intermediate
   44 PNG.  The default value is\~\fI300\fR.
   45 .TP
   46 \fB\-o\fR
   47 Use \fBopt-pdf\fR to minimize the filesize of intermediate PNG files before
   48 assembling the final PDF file.
   49 .TP
   50 \fB\-s\fR
   51 The \fBpdfidiff\fR utility will normally utilize GNU \fBparallel\fR (if present
   52 on the system) to perform operations in parallel to reduce computation time.
   53 Using this option will force single-threaded operation.
   54 .SH MODES
   55 .TP
   56 \fI1\fR
   57 Grayscale:  In this mode, both input files are converted to grayscale PNG
   58 files.  Any pixels that are darker (when comparing old to new) are highlighted
   59 in BLUE, and any pixels that are brighter are highlighted in RED.  [On a B&W
   60 drawing with a white background, this results in additions being highlighted in
   61 BLUE, and subtractions being highlighted in RED.]
   62 .TP
   63 \fI2\fR
   64 Grayscale (lightened):  This works much like the Grayscale analysis of mode 1,
   65 except that all unchanged pixels are shifted halfway towards white.  This makes
   66 it easier to identify changes on files where the background is predominantly
   67 white.
   68 .TP
   69 \fI3\fR
   70 Grayscale (darkened):  This works much like the Grayscale analysis of mode 1,
   71 except that all unchanged pixels are shifted halfway towards black.  This makes
   72 it easier to identify changes on files where the background is predominantly
   73 black.
   74 .TP
   75 \fI4\fR
   76 Color:  Here, the differences between the two files are computed on a per-RED,
   77 per-GREEN, and per-BLUE basis and are shifted and scaled such that unchanged
   78 pixels will show up as 50% gray.
   79 .TP
   80 \fI5\fR
   81 Color (stretched):  Again, differences between the two files are computed on a
   82 per-channel and are shifted that unchanged pixels will show up as 50% gray, but
   83 here the scaling is maximimized to emphasize differences.
   84 .SH NOTES
   85 The \fBpdfidiff\fR utility uses \fBpdftocairo\fR or \fBgs\fR to convert both
   86 input files into a series of PNG image files.  These files are then compared
   87 using \fBimagdiff\fR, and the resulting image "deltas" are reassemblied into a
   88 final PDF file using
   89 \fBimg2pdf\fR.
   90 .SH CAVEATS
   91 Because the input files are converted from PDF to PNG and are manipulated as
   92 bitmaps, the final PDF output will not contains any searchable string
   93 information, even if the input files did.  If you need to compare the text
   94 found in two different PDF files, you may have better luck with an alternate
   95 tool such as \fBdiffpdf\fR or \fBpdf-diff\fR.
   96 .SH "SEE ALSO"
   97 \fBgs\fR(1), \fBimg2pdf\fR(1), \fBparallel\fR(1), \fBimagdiff\fR(1),
   98 \fBdiffpdf\fR(1), \fBpdf-diff\fR(1), \fBpdftocairo\fR(1)
   99 .SH COPYRIGHT
  100 Copyright (C) 2018-2021 by Brian Lindholm. This program is free software; you
  101 can use it, redistribute it, and/or modify it under the terms of the GNU
  102 General Public License as published by the Free Software Foundation; either
  103 version 3, or (at your option) any later version.
  104 
  105 This program is distributed in the hope that it will be useful, but WITHOUT ANY
  106 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
  107 PARTICULAR PURPOSE.  See the GNU General Public License for more details.