Benjamin A. Beasley
10 months ago
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.TH OXIPNG "1" "March 2024" "" "User Commands"
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.SH NAME
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.B oxipng
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\(en Losslessly improve compression of PNG files
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.SH SYNOPSIS
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.B oxipng
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.RI [ OPTIONS ]
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.IR files ...
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.SH OPTIONS
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.SS ARGUMENTS
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.TP
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.IR files ...
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File(s) to compress (use
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.RB \(oq \- \(cq
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for stdin)
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.SS OPTIONS
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.TP
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.BR \-o ,\ \-\-opt\ \fIlevel
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Set the optimization level preset.
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The default level
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.B 2
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is quite fast and provides good compression.
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Lower levels are faster, higher levels provide better compression,
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though with increasingly diminishing returns.
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.RS
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.TP
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.B 0\ \[rA] \-\-zc\ 5\ \-\-fast
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(1 trial, determined heuristically)
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.TP
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.B 1\ \[rA] \-\-zc\ 10\ \-\-fast
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(1 trial, determined heuristically)
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.TP
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.B 2\ \[rA] \-\-zc\ 11\ \-f\ 0,1,6,7\ \-\-fast
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(4 fast trials, 1 main trial)
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.TP
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.B 3\ \[rA] \-\-zc\ 11\ \-f\ 0,7,8,9
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(4 trials)
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.TP
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.B 4\ \[rA] \-\-zc\ 12\ \-f\ 0,7,8,9
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(4 trials)
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.TP
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.B 5\ \[rA] \-\-zc\ 12\ \-f\ 0,1,2,5,6,7,8,9
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(8 trials)
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.TP
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.B 6\ \[rA] \-\-zc\ 12\ \-f\ 0-9
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(10 trials)
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.TP
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.B max\ \[rA]
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(stable alias for the max level)
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.RE
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.IP
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Manually specifying a compression option
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.RB ( zc ,
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.BR f ,
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etc.) will override the optimization preset,
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regardless of the order you write the arguments.
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.IP
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[default:
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.BR 2 ]
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.TP
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.BR \-r ,\ \-\-recursive
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When directories are given as input,
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traverse the directory trees and optimize all PNG files found
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(files with \(lq.png\(rq or \(lq.apng\(rq extension).
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.TP
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.B \-\-dir\ \fIdirectory
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Write output file(s) to
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.IR directory .
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If the directory does not exist, it will be created.
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Note that this will not preserve the directory structure
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of the input files when used with
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.BR \-\-recursive .
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.TP
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.B \-\-out\ \fIfile
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Write output file to
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.I file
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.TP
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.B \-\-stdout
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Write output to stdout
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.TP
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.BR \-p ,\ \-\-preserve
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Preserve file permissions and timestamps if possible
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.TP
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.BR \-P ,\ \-\-pretend
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Do not write any files, only show compression results
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.TP
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.B \-s
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Strip safely-removable chunks, same as
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.B \-\-strip\ safe
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.TP
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.BR \-\-strip\ \fImode
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Strip metadata chunks, where
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.I mode
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is one of:
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.RS
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.TP
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.B safe
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Strip all non-critical chunks, except for the following:
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cICP, iCCP, sRGB, pHYs, acTL, fcTL, fdAT
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.TP
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.B all
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Strip all non-critical chunks
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.TP
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.I list
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Strip chunks in the comma-separated list, e.g.\:
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.B bKGD,cHRM
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.RE
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.IP
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.IR CAUTION :
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.B all
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will convert APNGs to standard PNGs.
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.IP
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Note that
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.BR bKGD ,
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.B sBIT
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and
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.B hIST
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will be forcibly stripped if the color type or bit depth is changed,
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regardless of any options set.
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.TP
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.BR \-\-keep\ \fIlist
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Strip all metadata except in the comma-separated list
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.TP
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.BR \-a ,\ \-\-alpha
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Perform additional optimization on images with an alpha channel,
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by altering the color values of fully transparent pixels.
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This is generally recommended for better compression,
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but take care as while this is \(lqvisually lossless\(rq,
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it is technically a lossy transformation
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and may be unsuitable for some applications.
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.TP
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.BR \-i ,\ \-\-interlace\ \fItype
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Set the PNG interlacing type, where
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.I type
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is one of:
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.RS
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.TP
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.B 0
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Remove interlacing from all images that are processed
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.TP
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.B 1
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Apply Adam7 interlacing on all images that are processed
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.TP
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.B keep
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Keep the existing interlacing type of each image
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.RE
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.IP
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Note that interlacing can add 25-50% to the size of an optimized image.
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Only use it if you believe the benefits outweigh the costs for your use case.
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.IP
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[default:
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.BR 0 ]
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.TP
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.B \-\-scale16
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Forcibly reduce images with 16 bits per channel to 8 bits per channel.
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This is a lossy operation but can provide significant savings
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when you have no need for higher depth.
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Reduction is performed by scaling the values such that,
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e.g. 0x00FF is reduced to 0x01 rather than 0x00.
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.IP
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Without this flag, 16-bit images will only be reduced in depth
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if it can be done losslessly.
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.TP
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.BR \-v ,\ \-\-verbose ...
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Run in verbose mode (use twice to increase verbosity)
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.TP
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.BR \-q ,\ \-\-quiet
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Run in quiet mode
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.TP
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.BR \-f ,\ \-\-filers\ \fIlist
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Perform compression trials with each of the given filter types.
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You can specify a comma-separated list, or a range of values.
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E.g.\:
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.B \-f\ 0\-3
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is the same as
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.BR \-f\ 0,1,2,3 .
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.IP
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PNG delta filters (apply the same filter to every line)
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.RS
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.TP
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.B 0\ \[rA] None
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(recommended to always include this filter)
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.TP
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.B 1\ \[rA] Sub
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.TP
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.B 2\ \[rA] Up
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.TP
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.B 3\ \[rA] Average
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.TP
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.B 4\ \[rA] Paeth
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.RE
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.IP
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Heuristic strategies (try to find the best delta filter for each line)
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.RS
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.TP
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.B 5\ \[rA] MinSum
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Minimum sum of absolute differences
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.TP
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.B 6\ \[rA] Entropy
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Highest Shannon entropy
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.TP
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.B 7\ \[rA] Bigrams
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Lowest count of distinct bigrams
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.TP
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.B 8\ \[rA] BigEnt
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Highest Shannon entropy of bigrams
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.TP
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.B 9\ \[rA] Brute
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Smallest compressed size (slow)
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.RE
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.IP
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The default value depends on the optimization level preset.
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.TP
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.B \-\-fast
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Perform a fast compression evaluation of each enabled filter,
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followed by a single main compression trial of the best result.
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Recommended if you have more filters enabled than CPU cores.
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.TP
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.B \-\-zc\ \fIlevel
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Deflate compression level (1\-12) for main compression trials.
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The levels here are defined by the libdeflate compression library.
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.IP
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The default value depends on the optimization level preset.
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.TP
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.B \-\-nb
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Do not change bit depth
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.TP
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.B \-\-nc
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Do not change color type
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.TP
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.B \-\-np
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Do not change color palette
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.TP
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.B \-\-ng
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Do not change to or from grayscale
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.TP
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.B \-\-nx
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Do not perform any transformations and do not deinterlace by default.
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.TP
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.B \-\-nz
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Do not recompress IDAT unless required due to transformations.
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Recompression of other compressed chunks (such as iCCP) will also be disabled.
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Note that the combination of
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.B \-\-nx
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and
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.B \-\-nz
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will fully disable all optimization.
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.TP
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.B \-\-fix
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Do not perform checksum validation of PNG chunks.
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This may allow some files with errors to be processed successfully.
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.TP
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.B \-\-force
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Write the output even if it is larger than the input
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.TP
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.BR \-Z ,\ \-\-zopfli
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Use the much slower but stronger Zopfli compressor
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for main compression trials.
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Recommended use is with
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.B \-o\ max
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and
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.BR \-\-fast .
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.TP
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.B \-\-timeout\ \fIsecs
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Maximum amount of time, in seconds, to spend on optimizations.
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Oxipng will check the timeout
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before each transformation or compression trial,
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and will stop trying to optimize the file if the timeout is exceeded.
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Note that this does not cut short any operations that are already in progress,
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so it is currently of limited effectiveness
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for large files with high compression levels.
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.TP
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.BR \-t ,\ \-\-threads\ \fInum
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Set number of threads to use
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[default: num CPU cores]
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.TP
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.BR \-h ,\ \-\-help
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Print help (see a summary with
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.BR \-h )
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.TP
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.BR \-V ,\ \-\-version
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Print version
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.SH "SEE ALSO"
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.BR OPTIPNG (1)
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