afiq.hamzah
341 lines
15 KiB
Plaintext
341 lines
15 KiB
Plaintext
CWEBP(1) CWEBP(1)
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NAME
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cwebp - compress an image file to a WebP file
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SYNOPSIS
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cwebp [options] input_file -o output_file.webp
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DESCRIPTION
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This manual page documents the cwebp command.
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cwebp compresses an image using the WebP format. Input format can be
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either PNG, JPEG, TIFF, WebP or raw Y'CbCr samples. Note: Animated PNG
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and WebP files are not supported.
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OPTIONS
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The basic options are:
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-o string
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Specify the name of the output WebP file. If omitted, cwebp will
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perform compression but only report statistics. Using "-" as
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output name will direct output to 'stdout'.
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-- string
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Explicitly specify the input file. This option is useful if the
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input file starts with a '-' for instance. This option must
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appear last. Any other options afterward will be ignored.
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-h, -help
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A short usage summary.
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-H, -longhelp
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A summary of all the possible options.
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-version
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Print the version number (as major.minor.revision) and exit.
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-lossless
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Encode the image without any loss. For images with fully trans-
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parent area, the invisible pixel values (R/G/B or Y/U/V) will be
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preserved only if the -exact option is used.
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-near_lossless int
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Specify the level of near-lossless image preprocessing. This
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option adjusts pixel values to help compressibility, but has
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minimal impact on the visual quality. It triggers lossless com-
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pression mode automatically. The range is 0 (maximum preprocess-
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ing) to 100 (no preprocessing, the default). The typical value
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is around 60. Note that lossy with -q 100 can at times yield
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better results.
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-q float
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Specify the compression factor for RGB channels between 0 and
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100. The default is 75.
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In case of lossy compression (default), a small factor produces
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a smaller file with lower quality. Best quality is achieved by
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using a value of 100.
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In case of lossless compression (specified by the -lossless
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option), a small factor enables faster compression speed, but
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produces a larger file. Maximum compression is achieved by
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using a value of 100.
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-z int Switch on lossless compression mode with the specified level
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between 0 and 9, with level 0 being the fastest, 9 being the
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slowest. Fast mode produces larger file size than slower ones. A
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good default is -z 6. This option is actually a shortcut for
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some predefined settings for quality and method. If options -q
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or -m are subsequently used, they will invalidate the effect of
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this option.
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-alpha_q int
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Specify the compression factor for alpha compression between 0
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and 100. Lossless compression of alpha is achieved using a
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value of 100, while the lower values result in a lossy compres-
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sion. The default is 100.
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-preset string
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Specify a set of pre-defined parameters to suit a particular
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type of source material. Possible values are: default, photo,
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picture, drawing, icon, text. Since -preset overwrites the other
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parameters' values (except the -q one), this option should
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preferably appear first in the order of the arguments.
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-m int Specify the compression method to use. This parameter controls
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the trade off between encoding speed and the compressed file
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size and quality. Possible values range from 0 to 6. Default
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value is 4. When higher values are used, the encoder will spend
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more time inspecting additional encoding possibilities and
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decide on the quality gain. Lower value can result in faster
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processing time at the expense of larger file size and lower
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compression quality.
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-crop x_position y_position width height
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Crop the source to a rectangle with top-left corner at coordi-
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nates (x_position, y_position) and size width x height. This
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cropping area must be fully contained within the source rectan-
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gle. Note: the cropping is applied before any scaling.
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-resize width height
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Resize the source to a rectangle with size width x height. If
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either (but not both) of the width or height parameters is 0,
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the value will be calculated preserving the aspect-ratio. Note:
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scaling is applied after cropping.
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-mt Use multi-threading for encoding, if possible.
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-low_memory
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Reduce memory usage of lossy encoding by saving four times the
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compressed size (typically). This will make the encoding slower
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and the output slightly different in size and distortion. This
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flag is only effective for methods 3 and up, and is off by
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default. Note that leaving this flag off will have some side
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effects on the bitstream: it forces certain bitstream features
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like number of partitions (forced to 1). Note that a more
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detailed report of bitstream size is printed by cwebp when using
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this option.
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LOSSY OPTIONS
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These options are only effective when doing lossy encoding (the
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default, with or without alpha).
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-size int
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Specify a target size (in bytes) to try and reach for the com-
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pressed output. The compressor will make several passes of par-
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tial encoding in order to get as close as possible to this tar-
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get. If both -size and -psnr are used, -size value will prevail.
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-psnr float
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Specify a target PSNR (in dB) to try and reach for the com-
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pressed output. The compressor will make several passes of par-
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tial encoding in order to get as close as possible to this tar-
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get. If both -size and -psnr are used, -size value will prevail.
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-pass int
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Set a maximum number of passes to use during the dichotomy used
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by options -size or -psnr. Maximum value is 10, default is 1.
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If options -size or -psnr were used, but -pass wasn't specified,
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a default value of '6' passes will be used.
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-qrange int int
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Specifies the permissible interval for the quality factor. This
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is particularly useful when using multi-pass (-size or -psnr
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options). Default is 0 100. If the quality factor is outside
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this range, it will be clamped. If the minimum value must be
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less or equal to the maximum one.
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-af Turns auto-filter on. This algorithm will spend additional time
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optimizing the filtering strength to reach a well-balanced qual-
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ity.
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-jpeg_like
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Change the internal parameter mapping to better match the
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expected size of JPEG compression. This flag will generally pro-
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duce an output file of similar size to its JPEG equivalent (for
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the same -q setting), but with less visual distortion.
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Advanced options:
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-f int Specify the strength of the deblocking filter, between 0 (no
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filtering) and 100 (maximum filtering). A value of 0 will turn
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off any filtering. Higher value will increase the strength of
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the filtering process applied after decoding the picture. The
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higher the value the smoother the picture will appear. Typical
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values are usually in the range of 20 to 50.
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-sharpness int
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Specify the sharpness of the filtering (if used). Range is 0
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(sharpest) to 7 (least sharp). Default is 0.
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-strong
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Use strong filtering (if filtering is being used thanks to the
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-f option). Strong filtering is on by default.
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-nostrong
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Disable strong filtering (if filtering is being used thanks to
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the -f option) and use simple filtering instead.
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-sharp_yuv
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Use more accurate and sharper RGB->YUV conversion if needed.
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Note that this process is slower than the default 'fast'
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RGB->YUV conversion.
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-sns int
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Specify the amplitude of the spatial noise shaping. Spatial
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noise shaping (or sns for short) refers to a general collection
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of built-in algorithms used to decide which area of the picture
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should use relatively less bits, and where else to better trans-
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fer these bits. The possible range goes from 0 (algorithm is
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off) to 100 (the maximal effect). The default value is 50.
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-segments int
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Change the number of partitions to use during the segmentation
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of the sns algorithm. Segments should be in range 1 to 4.
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Default value is 4. This option has no effect for methods 3 and
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up, unless -low_memory is used.
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-partition_limit int
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Degrade quality by limiting the number of bits used by some mac-
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roblocks. Range is 0 (no degradation, the default) to 100 (full
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degradation). Useful values are usually around 30-70 for moder-
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ately large images. In the VP8 format, the so-called control
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partition has a limit of 512k and is used to store the following
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information: whether the macroblock is skipped, which segment it
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belongs to, whether it is coded as intra 4x4 or intra 16x16
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mode, and finally the prediction modes to use for each of the
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sub-blocks. For a very large image, 512k only leaves room to
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few bits per 16x16 macroblock. The absolute minimum is 4 bits
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per macroblock. Skip, segment, and mode information can use up
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almost all these 4 bits (although the case is unlikely), which
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is problematic for very large images. The partition_limit factor
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controls how frequently the most bit-costly mode (intra 4x4)
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will be used. This is useful in case the 512k limit is reached
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and the following message is displayed: Error code: 6 (PARTI-
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TION0_OVERFLOW: Partition #0 is too big to fit 512k). If using
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-partition_limit 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
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macroblock. See the -segments option.
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LOGGING OPTIONS
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These options control the level of output:
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-v Print extra information (encoding time in particular).
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-print_psnr
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Compute and report average PSNR (Peak-Signal-To-Noise ratio).
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-print_ssim
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Compute and report average SSIM (structural similarity metric,
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see https://en.wikipedia.org/wiki/SSIM for additional details).
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-print_lsim
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Compute and report local similarity metric (sum of lowest error
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amongst the collocated pixel neighbors).
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-progress
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Report encoding progress in percent.
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-quiet Do not print anything.
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-short Only print brief information (output file size and PSNR) for
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testing purposes.
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-map int
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Output additional ASCII-map of encoding information. Possible
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map values range from 1 to 6. This is only meant to help debug-
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ging.
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ADDITIONAL OPTIONS
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More advanced options are:
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-s width height
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Specify that the input file actually consists of raw Y'CbCr sam-
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ples following the ITU-R BT.601 recommendation, in 4:2:0 linear
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format. The luma plane has size width x height.
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-pre int
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Specify some preprocessing steps. Using a value of '2' will
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trigger quality-dependent pseudo-random dithering during
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RGBA->YUVA conversion (lossy compression only).
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-alpha_filter string
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Specify the predictive filtering method for the alpha plane. One
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of 'none', 'fast' or 'best', in increasing complexity and slow-
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ness order. Default is 'fast'. Internally, alpha filtering is
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performed using four possible predictions (none, horizontal,
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vertical, gradient). The 'best' mode will try each mode in turn
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and pick the one which gives the smaller size. The 'fast' mode
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will just try to form an a priori guess without testing all
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modes.
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-alpha_method int
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Specify the algorithm used for alpha compression: 0 or 1. Algo-
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rithm 0 denotes no compression, 1 uses WebP lossless format for
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compression. The default is 1.
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-exact Preserve RGB values in transparent area. The default is off, to
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help compressibility.
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-blend_alpha int
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This option blends the alpha channel (if present) with the
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source using the background color specified in hexadecimal as
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0xrrggbb. The alpha channel is afterward reset to the opaque
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value 255.
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-noalpha
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Using this option will discard the alpha channel.
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-hint string
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Specify the hint about input image type. Possible values are:
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photo, picture or graph.
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-metadata string
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A comma separated list of metadata to copy from the input to the
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output if present. Valid values: all, none, exif, icc, xmp.
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The default is none.
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Note: each input format may not support all combinations.
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-noasm Disable all assembly optimizations.
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BUGS
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Please report all bugs to the issue tracker:
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https://bugs.chromium.org/p/webp
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Patches welcome! See this page to get started: https://www.webmpro-
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ject.org/code/contribute/submitting-patches/
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EXAMPLES
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cwebp -q 50 -lossless picture.png -o picture_lossless.webp
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cwebp -q 70 picture_with_alpha.png -o picture_with_alpha.webp
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cwebp -sns 70 -f 50 -size 60000 picture.png -o picture.webp
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cwebp -o picture.webp -- ---picture.png
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AUTHORS
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cwebp is a part of libwebp and was written by the WebP team.
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The latest source tree is available at https://chromium.google-
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source.com/webm/libwebp
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This manual page was written by Pascal Massimino <pascal.mas-
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simino@gmail.com>, for the Debian project (and may be used by others).
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SEE ALSO
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dwebp(1), gif2webp(1)
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Please refer to https://developers.google.com/speed/webp/ for addi-
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tional information.
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March 17, 2022 CWEBP(1)
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