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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
5 .SH SYNOPSIS
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
23 Print help and quit.
26 Use ghostscript (\fBgs\fR) instead of poppler (\fBpdftocairo\fR) as the PDF
27 rendering engine.
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.
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.
39 Cause \fBpdfidiff\fR to silence the progress information normally printed
40 during operation.
43 Use the specified resolution (in DPI) when converting from PDF to intermediate
44 PNG. The default value is\~\fI300\fR.
47 Use \fBopt-pdf\fR to minimize the filesize of intermediate PNG files before
48 assembling the final PDF file.
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
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.]
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
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
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.
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
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.
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.