CWEBP(1) 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 YCbCr samples. 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 an for instance. This option must appear 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. q float Specify the compression factor for RGB channels between 0 and 100. The default is 75. 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. 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. preset string Specify a set of predefined parameters to suit a particular type of source material. Possible values are: default, photo, picture, drawing, icon, text. Sincepreset overwrites the other parameters values (except the q one), this option should preferably appear first in the order of the arguments. sns int Specify the amplitude of the spatial noise shaping. Spatial noise shaping (or sns for short) refers to a general collection of builtin 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 80. 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 decide on the quality gain. Lower value can result in faster processing time at the expense of larger file size and lower compression quality. jpeg_like Change the internal parameter mapping to better match the expected size of JPEG compression. This flag will generally pro duce an output file of similar size to its JPEG equivalent (for the sameq setting), but with less visual distortion. mt Use multithreading for encoding, if possible. This option is only effective when using lossy compression on a source with a transparency channel. 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 default. Note that leaving this flag off will have some side effects on the bitstream: it forces certain bitstream features like number of partitions (forced to 1). Note that a more detailed report of bitstream size is printed by cwebp when using this option. af Turns autofilter on. This algorithm will spend additional time optimizing the filtering strength to reach a wellbalanced qual ity. ADDITIONAL OPTIONS More advanced options are: 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 thef option) and use simple filtering instead. segments int Change the number of partitions to use during the segmentation of the sns algorithm. Segments should be in range 1 to 4. Default value is 4. This option has no effect for methods 3 and up, unlesslow_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 3070 for moder ately large images. In the VP8 format, the socalled 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 subblocks. For a very large image, 512k only leaves room to 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 bitcostly 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 thesegments option. size int Specify a target size (in bytes) to try and reach for the com pressed output. Compressor will make several pass of partial encoding in order to get as close as possible to this target. psnr float Specify a target PSNR (in dB) to try and reach for the com pressed output. Compressor will make several pass of partial encoding in order to get as close as possible to this target. pass int Set a maximum number of passes to use during the dichotomy used by optionssize orpsnr. Maximum value is 10. 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 aspectratio. crop x_position y_position width height Crop the source to a rectangle with topleft 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. s width height Specify that the input file actually consists of raw YCbCr sam ples following the ITUR BT.601 recommendation, in 4:2:0 linear format. The luma plane has size width x height. map int Output additional ASCIImap of encoding information. Possible map values range from 1 to 6. This is only meant to help debug ging. pre int Specify some preprocessing steps. Using a value of 2 will trigger qualitydependent pseudorandom 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 apriori 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. alpha_cleanup Modify unseen RGB values under fully transparent area, to help compressibility. The default is off. 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. lossless Encode the image without any loss. 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. v Print extra information (encoding time in particular). print_psnr Compute and report average PSNR (PeakSignalToNoise ratio). print_ssim Compute and report average SSIM (structural similarity metric, see http://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 purpose. BUGS Please report all bugs to our issue tracker: http://code.google.com/p/webp/issues Patches welcome! See this page to get started: http://www.webmpro ject.org/code/contribute/submittingpatches/ 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 was written by the WebP team. The latest source tree is available at http://www.webmproject.org/code This manual page was written by Pascal Massimino , for the Debian project (and may be used by others). SEE ALSO dwebp(1), gif2webp(1) Please refer to http://developers.google.com/speed/webp/ for additional information. July 22, 2014 CWEBP(1)