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CWEBP(1) General Commands Manual CWEBP(1) NAME cwebp - compress an image file to a WebP file SYNOPSIS cwebp [options] input_file -o output_file.webp DESCRIPTION This manual page documents the cwebp command. cwebp compresses an image using the WebP format. Input format can be either PNG, JPEG, TIFF, WebP or raw Y'CbCr samples. Note: Animated PNG and WebP files are not supported. OPTIONS The basic options are: -o string Specify the name of the output WebP file. If omitted, cwebp will perform compression but only report statistics. Using "-" as output name will direct output to 'stdout'. -- string Explicitly specify the input file. This option is useful if the input file starts with a '-' for instance. This option must ap- pear last. Any other options afterward will be ignored. -h, -help A short usage summary. -H, -longhelp A summary of all the possible options. -version Print the version number (as major.minor.revision) and exit. -lossless Encode the image without any loss. For images with fully trans- parent area, the invisible pixel values (R/G/B or Y/U/V) will be preserved only if the -exact option is used. -near_lossless int Specify the level of near-lossless image preprocessing. This op- tion adjusts pixel values to help compressibility, but has mini- mal impact on the visual quality. It triggers lossless compres- sion mode automatically. The range is 0 (maximum preprocessing) to 100 (no preprocessing, the default). The typical value is around 60. Note that lossy with -q 100 can at times yield better results. -q float Specify the compression factor for RGB channels between 0 and 100. The default is 75. In case of lossy compression (default), a small factor produces a smaller file with lower quality. Best quality is achieved by using a value of 100. In case of lossless compression (specified by the -lossless op- tion), a small factor enables faster compression speed, but pro- duces a larger file. Maximum compression is achieved by using a value of 100. -z int Switch on lossless compression mode with the specified level be- tween 0 and 9, with level 0 being the fastest, 9 being the slow- est. Fast mode produces larger file size than slower ones. A good default is -z 6. This option is actually a shortcut for some predefined settings for quality and method. If options -q or -m are subsequently used, they will invalidate the effect of this option. -alpha_q int Specify the compression factor for alpha compression between 0 and 100. Lossless compression of alpha is achieved using a value of 100, while the lower values result in a lossy compres- sion. The default is 100. -preset string Specify a set of pre-defined parameters to suit a particular type of source material. Possible values are: default, photo, picture, drawing, icon, text. Since -preset overwrites the other parameters' values (except the -q one), this option should preferably appear first in the order of the arguments. -m int Specify the compression method to use. This parameter controls the trade off between encoding speed and the compressed file size and quality. Possible values range from 0 to 6. Default value is 4. When higher values are used, the encoder will spend more time inspecting additional encoding possibilities and de- cide on the quality gain. Lower value can result in faster pro- cessing time at the expense of larger file size and lower com- pression quality. -crop x_position y_position width height Crop the source to a rectangle with top-left corner at coordi- nates (x_position, y_position) and size width x height. This cropping area must be fully contained within the source rectan- gle. Note: the cropping is applied before any scaling. -resize width height Resize the source to a rectangle with size width x height. If either (but not both) of the width or height parameters is 0, the value will be calculated preserving the aspect-ratio. Note: scaling is applied after cropping. -mt Use multi-threading for encoding, if possible. -low_memory Reduce memory usage of lossy encoding by saving four times the compressed size (typically). This will make the encoding slower and the output slightly different in size and distortion. This flag is only effective for methods 3 and up, and is off by de- fault. Note that leaving this flag off will have some side ef- fects on the bitstream: it forces certain bitstream features like number of partitions (forced to 1). Note that a more de- tailed report of bitstream size is printed by cwebp when using this option. LOSSY OPTIONS These options are only effective when doing lossy encoding (the de- fault, with or without alpha). -size int Specify a target size (in bytes) to try and reach for the com- pressed output. The compressor will make several passes of par- tial encoding in order to get as close as possible to this tar- get. If both -size and -psnr are used, -size value will prevail. -psnr float Specify a target PSNR (in dB) to try and reach for the com- pressed output. The compressor will make several passes of par- tial encoding in order to get as close as possible to this tar- get. If both -size and -psnr are used, -size value will prevail. -pass int Set a maximum number of passes to use during the dichotomy used by options -size or -psnr. Maximum value is 10, default is 1. If options -size or -psnr were used, but -pass wasn't specified, a default value of '6' passes will be used. If -pass is speci- fied, but neither -size nor -psnr are, a target PSNR of 40dB will be used. -qrange int int Specifies the permissible interval for the quality factor. This is particularly useful when using multi-pass (-size or -psnr op- tions). Default is 0 100. If the quality factor is outside this range, it will be clamped. If the minimum value must be less or equal to the maximum one. -af Turns auto-filter on. This algorithm will spend additional time optimizing the filtering strength to reach a well-balanced qual- ity. -jpeg_like Change the internal parameter mapping to better match the ex- pected size of JPEG compression. This flag will generally pro- duce an output file of similar size to its JPEG equivalent (for the same -q setting), but with less visual distortion. Advanced options: -f int Specify the strength of the deblocking filter, between 0 (no filtering) and 100 (maximum filtering). A value of 0 will turn off any filtering. Higher value will increase the strength of the filtering process applied after decoding the picture. The higher the value the smoother the picture will appear. Typical values are usually in the range of 20 to 50. -sharpness int Specify the sharpness of the filtering (if used). Range is 0 (sharpest) to 7 (least sharp). Default is 0. -strong Use strong filtering (if filtering is being used thanks to the -f option). Strong filtering is on by default. -nostrong Disable strong filtering (if filtering is being used thanks to the -f option) and use simple filtering instead. -sharp_yuv Use more accurate and sharper RGB->YUV conversion. Note that this process is slower than the default 'fast' RGB->YUV conver- sion. -sns int Specify the amplitude of the spatial noise shaping. Spatial noise shaping (or sns for short) refers to a general collection of built-in algorithms used to decide which area of the picture should use relatively less bits, and where else to better trans- fer these bits. The possible range goes from 0 (algorithm is off) to 100 (the maximal effect). The default value is 50. -segments int Change the number of partitions to use during the segmentation of the sns algorithm. Segments should be in range 1 to 4. De- fault value is 4. This option has no effect for methods 3 and up, unless -low_memory is used. -partition_limit int Degrade quality by limiting the number of bits used by some mac- roblocks. Range is 0 (no degradation, the default) to 100 (full degradation). Useful values are usually around 30-70 for moder- ately large images. In the VP8 format, the so-called control partition has a limit of 512k and is used to store the following information: whether the macroblock is skipped, which segment it belongs to, whether it is coded as intra 4x4 or intra 16x16 mode, and finally the prediction modes to use for each of the sub-blocks. For a very large image, 512k only leaves room for a few bits per 16x16 macroblock. The absolute minimum is 4 bits per macroblock. Skip, segment, and mode information can use up almost all these 4 bits (although the case is unlikely), which is problematic for very large images. The partition_limit factor controls how frequently the most bit-costly mode (intra 4x4) will be used. This is useful in case the 512k limit is reached and the following message is displayed: Error code: 6 (PARTI- TION0_OVERFLOW: Partition #0 is too big to fit 512k). If using -partition_limit is not enough to meet the 512k constraint, one should use less segments in order to save more header bits per macroblock. See the -segments option. Note the -m and -q op- tions also influence the encoder's decisions and ability to hit this limit. LOGGING OPTIONS These options control the level of output: -v Print extra information (encoding time in particular). -print_psnr Compute and report average PSNR (Peak-Signal-To-Noise ratio). -print_ssim Compute and report average SSIM (structural similarity metric, see https://en.wikipedia.org/wiki/SSIM for additional details). -print_lsim Compute and report local similarity metric (sum of lowest error amongst the collocated pixel neighbors). -progress Report encoding progress in percent. -quiet Do not print anything. -short Only print brief information (output file size and PSNR) for testing purposes. -map int Output additional ASCII-map of encoding information. Possible map values range from 1 to 6. This is only meant to help debug- ging. ADDITIONAL OPTIONS More advanced options are: -s width height Specify that the input file actually consists of raw Y'CbCr sam- ples following the ITU-R BT.601 recommendation, in 4:2:0 linear format. The luma plane has size width x height. -pre int Specify some preprocessing steps. Using a value of '2' will trigger quality-dependent pseudo-random dithering during RGBA->YUVA conversion (lossy compression only). -alpha_filter string Specify the predictive filtering method for the alpha plane. One of 'none', 'fast' or 'best', in increasing complexity and slow- ness order. Default is 'fast'. Internally, alpha filtering is performed using four possible predictions (none, horizontal, vertical, gradient). The 'best' mode will try each mode in turn and pick the one which gives the smaller size. The 'fast' mode will just try to form an a priori guess without testing all modes. -alpha_method int Specify the algorithm used for alpha compression: 0 or 1. Algo- rithm 0 denotes no compression, 1 uses WebP lossless format for compression. The default is 1. -exact Preserve RGB values in transparent area. The default is off, to help compressibility. -blend_alpha int This option blends the alpha channel (if present) with the source using the background color specified in hexadecimal as 0xrrggbb. The alpha channel is afterward reset to the opaque value 255. -noalpha Using this option will discard the alpha channel. -hint string Specify the hint about input image type. Possible values are: photo, picture or graph. -metadata string A comma separated list of metadata to copy from the input to the output if present. Valid values: all, none, exif, icc, xmp. The default is none. Note: each input format may not support all combinations. -noasm Disable all assembly optimizations. EXIT STATUS If there were no problems during execution, cwebp exits with the value of the C constant EXIT_SUCCESS. This is usually zero. If an error occurs, cwebp exits with the value of the C constant EXIT_FAILURE. This is usually one. EXAMPLES cwebp -q 50 -lossless picture.png -o picture_lossless.webp cwebp -q 70 picture_with_alpha.png -o picture_with_alpha.webp cwebp -sns 70 -f 50 -size 60000 picture.png -o picture.webp cwebp -o picture.webp -- ---picture.png AUTHORS cwebp is a part of libwebp and was written by the WebP team. The latest source tree is available at https://chromium.google- source.com/webm/libwebp This manual page was written by Pascal Massimino <pascal.mas- simino@gmail.com>, for the Debian project (and may be used by others). REPORTING BUGS Please report all bugs to the issue tracker: https://issues.webmpro- ject.org Patches welcome! See this page to get started: https://www.webmpro- ject.org/code/contribute/submitting-patches/ SEE ALSO dwebp(1), gif2webp(1) Please refer to https://developers.google.com/speed/webp/ for addi- tional information. September 17, 2024 CWEBP(1)
NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | EXAMPLES | AUTHORS | REPORTING BUGS | SEE ALSO
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