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    1 .TH OPT-PNG 1 "2021 Jan 15" littleutils
    2 .SH NAME
    3 opt-png \- losslessly optimize PNG image files
    4 .SH SYNOPSIS
    5 \fBopt-png\fR
    6 [\fB\-g(ray)\fR]
    7 [\fB\-h(elp)\fR]
    8 [\fB\-q(uiet)\fR]
    9 [\fB\-r(es)\fR\~\fIDPI\fR]
   10 [\fB\-t(ouch)\fR]
   11 \fIfile\|.\|.\|.\fR
   12 .SH DESCRIPTION
   13 \fBopt-png\fR losslessly optimizes PNG images by removing unused palette
   14 entries and/or optimizing the filtering algorithm.  This is accomplished using
   15 a combination of the \fBfilesize\fR, \fBpngcrush\fR, \fBpngrecolor\fR,
   16 \fBpngstrip\fR, and \fBtempname\fR utilities.
   17 .SH OPTIONS
   18 .TP
   19 \fB\-g\fR
   20 Force output to grayscale.
   21 .TP
   22 \fB\-h\fR
   23 Print help and quit.
   24 .TP
   25 \fB\-q\fR
   26 Quiet output.  No output commentary will be printed.
   27 .TP
   28 \fB\-r\fR\~\fIDPI\fR
   29 Write the specified resolution into the pHYs chunk of the output file.  Units
   30 are in pixels-per-inch.  To convert from pixels-per-meter, multiply by 0.0254
   31 (or divide by 39.37).  Note that this does not change the number of pixels in
   32 the image.  It only changes the assumed size of the pixels.
   33 .TP
   34 \fB\-t\fR
   35 Preserve timestamp on modified files.
   36 .SH EXAMPLES
   37 .TP
   38 Optimize a couple of image files:
   39 opt-png image001.png image002.png
   40 .TP
   41 Optimize all PNG images in an entire directory tree:
   42 find . -name "*.png" -exec opt-png {} \\;
   43 .TP
   44 Or alternatively, optimize all PNG images this way:
   45 find . -name "*.png" -print0 | xargs -0 opt-png
   46 .TP
   47 Fully utilize a quad-core system while optimizing all PNG images:
   48 find . -name "*.png" -print0 | xargs -0 -n 1 -P 4 opt-png
   49 .br
   50 find . -name "*.png" | parallel opt-png
   51 .SH NOTES
   52 If at all possible, make sure that \fBpngcrush\fR version \fI1.6.x\fR or later
   53 is running on your computer. It performs substantially better than
   54 \fBpngcrush\fR \fI1.5.10\fR (and earlier) on black-and-white (and other
   55 low-color) images due to use of the Z_RLE zlib strategy.
   56 .SH "SEE ALSO"
   57 \fBfilesize\fR(1), \fBpngcrush\fR(1), \fBpngrecolor\fR(1), \fBpngstrip\fR(1),
   58 \fBtempname\fR(1)
   59 .SH COPYRIGHT
   60 Copyright (C) 2004-2021 by Brian Lindholm.  This program is free software; you
   61 can use it, redistribute it, and/or modify it under the terms of the GNU
   62 General Public License as published by the Free Software Foundation; either
   63 version 3, or (at your option) any later version.
   64 
   65 This program is distributed in the hope that it will be useful, but WITHOUT ANY
   66 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
   67 PARTICULAR PURPOSE.  See the GNU General Public License for more details.