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man/cwebp: group lossy-only options
+ reorder / regroup other options based on basic vs. advanced + logging Change-Id: I1cedef08e29f516952671f9e64771ee108e80867
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James Zern
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man/cwebp.1
166
man/cwebp.1
@ -1,5 +1,5 @@
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.\" Hey, EMACS: -*- nroff -*-
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.TH CWEBP 1 "October 19, 2015"
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.TH CWEBP 1 "November 02, 2015"
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.SH NAME
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cwebp \- compress an image file to a WebP file
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.SH SYNOPSIS
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@ -35,6 +35,15 @@ A summary of all the possible options.
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.B \-version
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Print the version number (as major.minor.revision) and exit.
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.TP
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.B \-lossless
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Encode the image without any loss.
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.TP
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.BI \-near_lossless " int
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Use near-lossless image preprocessing. This option adjusts pixel values
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to help compressibility, but has minimal impact on the visual quality.
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It triggers lossless compression mode automatically.
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Range is 0 (maximum preprocessing) to 100 (no preprocessing, the default).
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.TP
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.BI \-q " float
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Specify the compression factor for RGB channels between 0 and 100. The default
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is 75.
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@ -59,13 +68,6 @@ Specify the compression factor for alpha compression between 0 and 100.
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Lossless compression of alpha is achieved using a value of 100, while the lower
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values result in a lossy compression. The default is 100.
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.TP
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.BI \-f " int
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Specify the strength of the deblocking filter, between 0 (no filtering)
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and 100 (maximum filtering). A value of 0 will turn off any filtering.
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Higher value will increase the strength of the filtering process applied
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after decoding the picture. The higher the value the smoother the picture will
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appear. Typical values are usually in the range of 20 to 50.
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.TP
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.BI \-preset " string
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Specify a set of pre-defined parameters to suit a particular type of
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source material. Possible values are: \fBdefault\fP, \fBphoto\fP,
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@ -74,13 +76,6 @@ source material. Possible values are: \fBdefault\fP, \fBphoto\fP,
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\fB\-q\fP one), this option should preferably appear first in the
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order of the arguments.
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.TP
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.BI \-sns " int
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Specify the amplitude of the spatial noise shaping. Spatial noise shaping
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(or \fBsns\fP for short) refers to a general collection of built-in algorithms
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used to decide which area of the picture should use relatively less bits,
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and where else to better transfer these bits. The possible range goes from
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0 (algorithm is off) to 100 (the maximal effect). The default value is 80.
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.TP
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.BI \-m " int
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Specify the compression method to use. This parameter controls the
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trade off between encoding speed and the compressed file size and quality.
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@ -90,11 +85,15 @@ additional encoding possibilities and decide on the quality gain.
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Lower value can result in faster processing time at the expense of
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larger file size and lower compression quality.
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.TP
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.B \-jpeg_like
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Change the internal parameter mapping to better match the expected size
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of JPEG compression. This flag will generally produce an output file of
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similar size to its JPEG equivalent (for the same \fB\-q\fP setting), but
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with less visual distortion.
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.BI \-resize " width height
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Resize the source to a rectangle with size \fBwidth\fP x \fBheight\fP.
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If either (but not both) of the \fBwidth\fP or \fBheight\fP parameters is 0,
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the value will be calculated preserving the aspect-ratio.
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.TP
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.BI \-crop " x_position y_position width height
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Crop the source to a rectangle with top-left corner at coordinates
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(\fBx_position\fP, \fBy_position\fP) and size \fBwidth\fP x \fBheight\fP.
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This cropping area must be fully contained within the source rectangle.
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.TP
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.B \-mt
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Use multi-threading for encoding, if possible. This option is only effective
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@ -108,13 +107,46 @@ different in size and distortion. This flag is only effective for methods
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some side effects on the bitstream: it forces certain bitstream features
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like number of partitions (forced to 1). Note that a more detailed report
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of bitstream size is printed by \fBcwebp\fP when using this option.
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.SS LOSSY OPTIONS
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These options are only effective when doing lossy encoding (the default, with
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or without alpha).
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.TP
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.BI \-size " int
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Specify a target size (in bytes) to try and reach for the compressed output.
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Compressor will make several pass of partial encoding in order to get as
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close as possible to this target.
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.TP
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.BI \-psnr " float
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Specify a target PSNR (in dB) to try and reach for the compressed output.
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Compressor will make several pass of partial encoding in order to get as
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close as possible to this target.
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.TP
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.BI \-pass " int
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Set a maximum number of passes to use during the dichotomy used by
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options \fB\-size\fP or \fB\-psnr\fP. Maximum value is 10.
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.TP
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.B \-af
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Turns auto-filter on. This algorithm will spend additional time optimizing
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the filtering strength to reach a well-balanced quality.
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.TP
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.B \-jpeg_like
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Change the internal parameter mapping to better match the expected size
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of JPEG compression. This flag will generally produce an output file of
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similar size to its JPEG equivalent (for the same \fB\-q\fP setting), but
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with less visual distortion.
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.SH ADDITIONAL OPTIONS
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More advanced options are:
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.TP
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Advanced options:
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.TP
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.BI \-f " int
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Specify the strength of the deblocking filter, between 0 (no filtering)
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and 100 (maximum filtering). A value of 0 will turn off any filtering.
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Higher value will increase the strength of the filtering process applied
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after decoding the picture. The higher the value the smoother the picture will
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appear. Typical values are usually in the range of 20 to 50.
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.TP
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.BI \-sharpness " int
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Specify the sharpness of the filtering (if used).
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@ -128,6 +160,13 @@ Use strong filtering (if filtering is being used thanks to the
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Disable strong filtering (if filtering is being used thanks to the
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\fB\-f\fP option) and use simple filtering instead.
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.TP
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.BI \-sns " int
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Specify the amplitude of the spatial noise shaping. Spatial noise shaping
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(or \fBsns\fP for short) refers to a general collection of built-in algorithms
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used to decide which area of the picture should use relatively less bits,
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and where else to better transfer these bits. The possible range goes from
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0 (algorithm is off) to 100 (the maximal effect). The default value is 80.
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.TP
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.BI \-segments " int
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Change the number of partitions to use during the segmentation of the
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sns algorithm. Segments should be in range 1 to 4. Default value is 4.
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@ -152,40 +191,45 @@ useful in case the 512k limit is reached and the following message is displayed:
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If using \fB-partition_limit\fP is not enough to meet the 512k constraint, one
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should use less segments in order to save more header bits per macroblock.
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See the \fB-segments\fP option.
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.SS LOGGING OPTIONS
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These options control the level of output:
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.TP
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.BI \-size " int
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Specify a target size (in bytes) to try and reach for the compressed output.
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Compressor will make several pass of partial encoding in order to get as
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close as possible to this target.
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.B \-v
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Print extra information (encoding time in particular).
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.TP
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.BI \-psnr " float
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Specify a target PSNR (in dB) to try and reach for the compressed output.
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Compressor will make several pass of partial encoding in order to get as
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close as possible to this target.
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.B \-print_psnr
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Compute and report average PSNR (Peak-Signal-To-Noise ratio).
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.TP
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.BI \-pass " int
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Set a maximum number of passes to use during the dichotomy used by
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options \fB\-size\fP or \fB\-psnr\fP. Maximum value is 10.
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.B \-print_ssim
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Compute and report average SSIM (structural similarity
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metric, see http://en.wikipedia.org/wiki/SSIM for additional details).
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.TP
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.BI \-resize " width height
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Resize the source to a rectangle with size \fBwidth\fP x \fBheight\fP.
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If either (but not both) of the \fBwidth\fP or \fBheight\fP parameters is 0,
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the value will be calculated preserving the aspect-ratio.
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.B \-print_lsim
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Compute and report local similarity metric (sum of lowest error amongst the
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collocated pixel neighbors).
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.TP
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.BI \-crop " x_position y_position width height
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Crop the source to a rectangle with top-left corner at coordinates
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(\fBx_position\fP, \fBy_position\fP) and size \fBwidth\fP x \fBheight\fP.
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This cropping area must be fully contained within the source rectangle.
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.B \-progress
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Report encoding progress in percent.
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.TP
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.B \-quiet
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Do not print anything.
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.TP
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.B \-short
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Only print brief information (output file size and PSNR) for testing purpose.
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.TP
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.BI \-map " int
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Output additional ASCII-map of encoding information. Possible map values
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range from 1 to 6. This is only meant to help debugging.
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.SS ADDITIONAL OPTIONS
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More advanced options are:
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.TP
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.BI \-s " width height
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Specify that the input file actually consists of raw Y'CbCr samples following
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the ITU-R BT.601 recommendation, in 4:2:0 linear format.
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The luma plane has size \fBwidth\fP x \fBheight\fP.
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.TP
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.BI \-map " int
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Output additional ASCII-map of encoding information. Possible map values
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range from 1 to 6. This is only meant to help debugging.
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.TP
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.BI \-pre " int
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Specify some pre-processing steps. Using a value of '2' will trigger
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quality-dependent pseudo-random dithering during RGBA->YUVA conversion
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@ -215,15 +259,6 @@ afterward reset to the opaque value 255.
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.B \-noalpha
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Using this option will discard the alpha channel.
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.TP
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.B \-lossless
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Encode the image without any loss.
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.TP
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.BI \-near_lossless " int
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Use near-lossless image preprocessing. This option adjusts pixel values
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to help compressibility, but has minimal impact on the visual quality.
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It triggers lossless compression mode automatically.
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Range is 0 (maximum preprocessing) to 100 (no preprocessing, the default).
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.TP
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.BI \-hint " string
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Specify the hint about input image type. Possible values are:
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\fBphoto\fP, \fBpicture\fP or \fBgraph\fP.
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@ -238,29 +273,6 @@ Note: each input format may not support all combinations.
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.TP
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.B \-noasm
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Disable all assembly optimizations.
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.TP
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.B \-v
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Print extra information (encoding time in particular).
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.TP
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.B \-print_psnr
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Compute and report average PSNR (Peak-Signal-To-Noise ratio).
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.TP
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.B \-print_ssim
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Compute and report average SSIM (structural similarity
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metric, see http://en.wikipedia.org/wiki/SSIM for additional details).
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.TP
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.B \-print_lsim
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Compute and report local similarity metric (sum of lowest error amongst the
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collocated pixel neighbors).
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.TP
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.B \-progress
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Report encoding progress in percent.
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.TP
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.B \-quiet
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Do not print anything.
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.TP
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.B \-short
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Only print brief information (output file size and PSNR) for testing purpose.
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.SH BUGS
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Please report all bugs to our issue tracker:
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