CWEBP(1)

👑 CWEBP(1) — General Commands Manual 👑

okay bestie, sit down, hydrate, because we're about to learn cwebp and it's genuinely iconic ✨ this is the cwebp manual page, she's a General Commands Manual girlie, and she's about to teach you how to turn your pics into WebP files 💅

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🌸 NAME 🌸

cwebp — compress an image file to a WebP file 🦋

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🎀 SYNOPSIS 🎀

cwebp [options] input_file -o output_file.webp

like. that's it. that's the whole vibe. input in, options sprinkled, WebP out 💖

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✨ DESCRIPTION ✨

This manual page documents the cwebp command, fr fr.

cwebp compresses an image using the WebP format. The input format can be either PNG, JPEG, TIFF, WebP or raw Y'CbCr samples — pick your fighter 🫶

🚨 NOT ME FORGETTING TO MENTION: Animated PNG and WebP files are not supported. like, at all. don't come for her, she said what she said 💀

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💅 OPTIONS 💅

The basic options are, and I'm obsessed with all of them:

• -o string — Specify the name of the output WebP file. If you skip it, cwebp will still perform compression but only report statistics. And if you use "-" as the output name, output gets directed to 'stdout' ✨
• -- string — Explicitly specify the input file. Super useful if your input file starts with a - for instance (chaotic of it). This option must appear last. Any other options after it will be ignored, periodt 🙈
• -h, -help — A short usage summary. The little snack. 🍓
• -H, -longhelp — A summary of all the possible options. The full meal. 👑
• -version — Print the version number (as major.minor.revision) and exit. She's brief, she's efficient, she ate.
• -lossless — Encode the image without any loss. For images with fully transparent 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 option adjusts pixel values to help compressibility, but has minimal impact on the visual quality. It triggers lossless compression 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 option), a small factor enables faster compression speed, but produces a larger file. Maximum compression is achieved by using a value of 100. (yes the same number does different things depending on the mode, that's just her duality 💅)
• -z int — Switch on lossless compression mode with the specified level between 0 and 9, with level 0 being the fastest, 9 being the slowest. 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 compression. 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 decide on the quality gain. Lower value can result in faster processing time at the expense of larger file size and lower compression quality ⚖️
• -crop x_position y_position width height — Crop the source to a rectangle with top-left corner at coordinates (x_position, y_position) and size width x height. This cropping area must be fully contained within the source rectangle. 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 🦋
• -resize_mode string — Specify the behavior of the -resize option. Possible values are: down_only, up_only, always (default). down_only will use the values specified by -resize if either the input width or height are larger than the given dimensions. Similarly, up_only will only resize if either the input width or height are smaller than the given dimensions 🎚️
• -mt — Use multi-threading for encoding, if possible. more cores more slay 🔥
• -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 🧠

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🍓 LOSSY OPTIONS 🍓

These options are only effective when doing lossy encoding (the default, with or without alpha). iykyk 💜

• -size int — Specify a target size (in bytes) to try and reach for the compressed output. The compressor will make several passes of partial encoding in order to get as close as possible to this target. 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 compressed output. The compressor will make several passes of partial encoding in order to get as close as possible to this target. 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 specified, 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 options). 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 quality ✨
• -jpeg_like — Change the internal parameter mapping to better match the expected size of JPEG compression. This flag will generally produce 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 conversion ⚡
• -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 transfer 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. Default 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 macroblocks. Range is 0 (no degradation, the default) to 100 (full degradation). Useful values are usually around 30-70 for moderately 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 (PARTITION0_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 options also influence the encoder's decisions and ability to hit this limit 😭

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🌈 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 — does the math and reports the average SSIM (that's the structural similarity metric, and yeah there's a whole Wikipedia page on it: https://en.wikipedia.org/wiki/SSIM if you wanna go down that rabbit hole 🦋).
• -print_lsim — computes and reports the local similarity metric, which is the sum of the lowest error amongst the collocated pixel neighbors. fancy 💅
• -progress — reports encoding progress in percent, so you can watch the little number go up 📈
• -quiet — do not print anything. silence. peace. 🤫
• -short — only prints brief info (output file size and PSNR) for testing purposes.
• -map int — outputs an extra ASCII-map of encoding information. Possible map values range from 1 to 6. ngl this one is literally only meant to help debugging, it's not for the general public 🔧

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✨ ADDITIONAL OPTIONS ✨

okay so these are the more advanced ones, bestie. buckle up 🎀

• -s width height — tells cwebp that your input file is actually made of raw Y'CbCr samples following the ITU-R BT.601 recommendation, in 4:2:0 linear format. The luma plane has size width x height.
• -pre int — sets some preprocessing steps. If you pass a value of '2', it'll trigger quality-dependent pseudo-random dithering during RGBA->YUVA conversion (lossy compression only, so heads up 👀).
• -alpha_filter string — picks the predictive filtering method for the alpha plane. Options are 'none', 'fast' or 'best', listed in increasing complexity and slowness order. Default is 'fast'. Internally, alpha filtering runs using four possible predictions (none, horizontal, vertical, gradient). The 'best' mode will try each mode in turn and pick whichever gives the smaller size. The 'fast' mode just tries to form an a priori guess without testing all the modes. lowkey efficient ✨
• -alpha_method int — picks the algorithm used for alpha compression: 0 or 1. Algorithm 0 means no compression, 1 uses WebP lossless format for compression. The default is 1.
• -exact — preserves RGB values in transparent areas. The default is off, because leaving it off helps compressibility.
• -blend_alpha int — this option blends the alpha channel (if present) with the source using the background color you specify in hexadecimal as 0xrrggbb. The alpha channel is afterward reset to the opaque value 255.
• -noalpha — using this option will discard the alpha channel. gone. bye. 👋
• -hint string — gives a hint about the 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. so don't come for cwebp when your format doesn't have that metadata, bestie 😭

• -noasm — disables all assembly optimizations. 🛑

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🌈 EXIT STATUS 🌈

If there were no problems during execution, cwebp exits with the value of the C constant EXIT_SUCCESS. This is usually zero. slay, no notes 💖

If an error occurs, cwebp exits with the value of the C constant EXIT_FAILURE. This is usually one. 💀

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🌸 EXAMPLES 🌸

here's the vibe, copy these directly:

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

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👑 AUTHORS 👑

cwebp is a part of libwebp and was written by the WebP team.

The latest source tree is available at https://chromium.googlesource.com/webm/libwebp

This manual page was written by Pascal Massimino <pascal.massimino@gmail.com>, for the Debian project (and may be used by others).

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🫶 REPORTING BUGS 🫶

Please report all bugs to the issue tracker: https://issues.webmproject.org

Patches welcome! See this page to get started: https://www.webmproject.org/code/contribute/submitting-patches/

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⭐ SEE ALSO ⭐

dwebp(1), gif2webp(1)

Please refer to https://developers.google.com/speed/webp/ for additional information.

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and that's the whole page, bestie 💅✨ this one comes from the libwebp source tree and it's dated April 10, 2025 — go forth and encode, you absolute icon 🎀🦋