WebP

WebP is Google’s image format from 2010: a lossy mode derived from the VP8 video codec, a separate lossless mode (VP8L) added in 2011, and an extended container with alpha, animation, ICC profiles and Exif/XMP metadata. It is standardised as RFC 9649 (informational, 2024) and implemented by Google’s libwebp, which provides cwebp, dwebp, img2webp, gif2webp and webpmux.

Its appeal today is compatibility: every current browser, OS image framework and image library decodes it, and it encodes quickly. Newer formats (AVIF, JPEG XL) compress better, but WebP is a safe default for web delivery, for transparent images and for replacing GIF.

Strengths and weaknesses

Strengths

• Lossy files noticeably smaller than JPEG at similar visual quality in most cases, with alpha available in lossy files too.
• A lossless mode that is clearly smaller than PNG: on Google’s web-image corpus about 40 % smaller than plain libpng output and about 20 % smaller than ZopfliPNG-optimised PNG.
• Animation with 24-bit colour and alpha, and per-frame lossy or lossless coding. Animated WebP is usually considerably smaller than GIF.
• Universal support, fast encoding and decoding, royalty-free.

Weaknesses

• Lossy WebP is 8-bit 4:2:0 only. There is no 4:4:4 or 10-bit lossy mode and no HDR, so saturated red/blue edges and coloured text bleed, and gradients can band.
• Maximum 16,383 × 16,383 pixels in each direction.
• The lossy format is based on VP8 and tends to smooth fine texture; it is clearly less efficient than AVIF or JPEG XL.
• No JPEG-style progressive decode.
• Lossless is 8-bit RGBA only; for 16-bit images use PNG or JPEG XL.

Support

Browser	WebP
Chrome	17+ (lossless and alpha from 23, animation from 32)
Edge	18+
Firefox	65+
Safari / iOS Safari	14+

(From MDN’s WebP data.) That covers every browser still in use. Older software and some editors and apps are the remaining gaps. See image and audio support.

Encode with cwebp

cwebp reads PNG, JPEG, TIFF, WebP and PNM.

cwebp -q 80 -m 6 input.png -o output.webp

-q is 0–100 (default 75); the scale is not JPEG’s, so compare by eye. -m 6 is the slowest, best compression method (default 4) and is worth it unless you are encoding enormous batches. Add -mt to use several threads.

Goal	Command	Notes
Photo	cwebp -q 80 -m 6 in.png -o out.webp	-preset photo, picture, drawing, icon and text tune the encoder for the content type; the preset must come first.
Sharper colour edges	add -sharp_yuv	Slower, more careful RGB→YUV 4:2:0 conversion; helps red text and thin coloured lines.
Lossless	cwebp -lossless -z 9 in.png -o out.webp	-z 0–9 is the lossless effort preset (-z implies -lossless); 9 is slowest and smallest.
Lossless with a little loss	cwebp -near_lossless 60 -z 9 in.png -o out.webp	-near_lossless 0..100: 100 is off; lower is lossier. Still the lossless codec, so graphics compress better with no visible change.
Smaller alpha	cwebp -q 80 -alpha_q 80 in.png -o out.webp	Alpha is coded separately and is lossless by default (-alpha_q 100); lower it to shrink soft masks.
Keep hidden RGB under transparency	add -exact	By default cwebp is free to change colours of fully transparent pixels to compress better.
Hit a size	cwebp -size 50000 in.png -o out.webp	Searches quality for a target byte size. -psnr 42 targets a PSNR instead.
Resize while encoding	cwebp -resize 1280 0 -q 80 in.png -o out.webp	0 keeps the aspect ratio.

With -lossless, -q no longer sets quality; it behaves as effort. Use -z instead.

Metadata and colour

cwebp writes no metadata by default, including ICC profiles. Wide-gamut images will look desaturated if you drop their profile, so pass -metadata icc (or -metadata all for Exif, XMP and ICC) when the source has one. cwebp does not apply Exif orientation to the pixels, so a rotated phone photo converted with the default -metadata none comes out sideways; rotate it first or keep the Exif.

Animation

gif2webp -lossy -q 70 -m 6 input.gif -o output.webp
img2webp -loop 0 -lossy -q 70 -d 100 frame1.png frame2.png frame3.png -o animation.webp

gif2webp is lossless unless you add -lossy or -mixed (per-frame choice); -min_size searches for the smallest result. img2webp takes explicit frame lists with a per-frame -d duration in milliseconds and per-frame -lossy/-lossless/-q. For video clips, AVIF animations or a real video format are much smaller. webpmux edits and inspects frames and chunks. dwebp only decodes still images; use anim_dump or a viewer for animations.

Pitfalls

• Lossless is for graphics, screenshots and masters. A lossless WebP of a photograph is several times the size of a lossy one.
• -q 100 is lossy, not lossless; use -lossless.
• The 16,383-pixel limit applies in both modes; downscale or split larger images first.
• WebP files fed from lossy JPEGs compound loss; encode from the original where possible.
• libwebp’s lossless decoder had a heap overflow, CVE-2023-4863, that was exploited in the wild in 2023. If you embed libwebp to decode untrusted uploads, keep it current.

Related pages

• AVIF and JPEG XL compress better and support more bit depths.
• JPEG and PNG are the formats WebP most often replaces.
• VP8 is the video codec behind lossy WebP.

Full option reference

The tables below are the full parameter references for cwebp, img2webp and gif2webp in libwebp 1.6.0. Reading option tables explains the Default column.

cwebp parameter reference

Complete cwebp 1.6.0 options and defaults

Parameter and aliases	Type / accepted values	Default	Meaning and limits
-preset	enum	default	Start from a tuned set (default, photo, picture, drawing, icon, text); resets other options, so put it first.
-q	float 0–100	75	Lossy quality 0–100, or lossless effort with -lossless. Disables -z.
-m	integer 0–6	4	Speed/size trade-off, 0 fast to 6 slowest and smallest. Disables -z.
-z	integer 0–9	not enabled	Lossless preset 0 (fast) to 9 (slowest); implies -lossless and is ignored if -q or -m is given.
-lossless	switch	off	Encode with lossless VP8L instead of lossy VP8.
-near_lossless	integer 0–100	100 (no preprocessing)	Lossless with pixel preprocessing: 100 is off, lower values discard more detail for smaller files.
-hint	enum	default	Content hint for lossless coding: photo, picture or graph.
-alpha_q	integer 0–100	100	Alpha-plane quality 0–100; below 100 makes alpha lossy, independent of -q.
-alpha_method	integer 0–1	1	Alpha compression: 0 stores it raw, 1 uses lossless coding.
-alpha_filter	enum	fast	Alpha-plane prediction filter: none, fast or best.
-exact	switch	off	Keep RGB values under fully transparent pixels instead of zeroing them.
-alpha_cleanup	switch	off (-exact is off)	Hidden obsolete flag that turns -exact off; has no other effect.
-noalpha	switch	off	Discard the alpha channel.
-blend_alpha	hex RGB	not enabled	Composite onto a hex RGB background (e.g. 0xffffff) and drop transparency.
-segments	integer 1–4	4	Number of VP8 segments, 1–4; fewer is faster but less adaptive.
-sns	integer 0–100	50	Spatial noise shaping 0–100; higher spends bits on perceptually important areas.
-f	integer 0–100	60	Loop-filter strength 0–100; 0 turns filtering off.
-sharpness	integer 0–7	0	Loop-filter sharpness 0 (most smoothing) to 7 (least).
-strong	switch	on	Use the strong loop filter, which also filters chroma.
-nostrong	switch	off	Use the simple loop filter, which is faster.
-sharp_yuv	switch	off	Slower RGB-to-YUV conversion that preserves sharp color edges better.
-partition_limit	integer 0–100	0	Allow quality loss 0–100 so the first partition fits its 512 KiB limit.
-size	nonnegative integer bytes	0 (no target)	Target output size in bytes (lossy only); approximate. Raises -pass from 1 to 6.
-psnr	nonnegative float dB	0 (no target)	Target PSNR in dB (around 42 is typical); overrides -size. Lossy only.
-pass	integer 1–10	1; becomes 6 for a size/PSNR target	Analysis passes 1–10 for size or PSNR targeting; more is slower and closer to target.
-qrange	two integers	0 100	Limit the quality search to MIN MAX within 0–100.
-af	switch	off	Experimental: adjust filter strength automatically.
-jpeg_like	switch	off	Experimental: remap parameters so output size roughly matches JPEG’s, with less degradation.
-pre	integer bitfield 0–7	0	Experimental preprocessing bits: 1 segment smoothing, 2 dithering, 4 sharp YUV conversion.
-mt	switch	off	Use multithreading where available.
-low_memory	switch	off	Use less memory at the cost of speed.
-s	two positive integers	not specified	Declare raw YUV420 input of WIDTH HEIGHT; not a resize.
-crop	four integers x y width height	not enabled	Crop to X Y WIDTH HEIGHT before any resize.
-resize	two nonnegative integers	not enabled	Resize to WIDTH HEIGHT after cropping; a zero dimension keeps the aspect ratio.
-resize_mode	enum	always	When -resize applies: always, up_only or down_only.
-metadata	comma-separated tokens	none	Copy metadata from the input: all, none, exif, icc, xmp (comma-separated).
-o	path	none (encode without saving)	Output file; - writes to stdout.
-d	PGM path	not enabled	Write the decoded result of the lossy encode to a PGM file for inspection.
-map	integer	not enabled	Print a diagnostic map of encoder statistics; debugging only.
-print_psnr	switch	off	Print PSNR of the encoded result against the source.
-print_ssim	switch	off	Print SSIM of the encoded result against the source.
-print_lsim	switch	off	Print local-similarity score of the encoded result.
-short	switch	off	Print a condensed statistics summary.
-quiet	switch	off	Print nothing.
-v	switch	off	Print timing and extra diagnostics.
-progress	switch	off	Print encoding progress as a percentage.
-noasm	switch	off	Disable assembly optimizations (SSE, NEON); for debugging.
-h, -help	action	not requested	Print the short help.
-H, -longhelp	action	not requested	Print the full help.
-version	action	not requested	Print the library and libsharpyuv versions, then exit.
--	action	not requested	Treat the next argument as the input file and stop parsing options.

img2webp parameter reference

Complete img2webp 1.6.0 options and defaults

Parameter and aliases	Type / accepted values	Default	Meaning and limits
-o	path	none (encode without saving)	Output animation file; - writes to stdout.
-loop	nonnegative integer	0 (infinite)	Animation loop count; 0 loops forever.
-min_size	switch	off	Spend more time to minimize size; disables inserted keyframes.
-kmin	integer	2147483646	Minimum frames between keyframes; the default effectively disables inserted keyframes.
-kmax	integer	2147483647	Maximum frames between keyframes; 1 makes every frame a keyframe, 0 or less disables inserted ones.
-mixed	switch	off	Pick lossy or lossless per frame automatically; per-frame -lossy and -lossless are then ignored.
-near_lossless	integer 0–100	100 (no preprocessing)	Near-lossless preprocessing 0–100 for lossless frames; 100 is off.
-sharp_yuv	switch	off	Slower RGB-to-YUV conversion with better edges, for lossy frames.
-v	switch	off	Print frame order and timestamps.
-h, -help	action	not requested	Print help.
-version	action	not requested	Print encoder, mux and libsharpyuv versions, then exit.
-d	positive integer milliseconds	100	Display time in milliseconds for this and following frames.
-lossless	switch	on	Encode following frames losslessly (the default).
-lossy	switch	off	Encode following frames lossily.
-q	float 0–100	75	Quality 0–100 for following frames; lossless effort when lossless.
-m	integer 0–6	4	Speed/size trade-off 0–6 for following frames; 6 is slowest and smallest.
-exact	switch	off	Keep RGB under transparent pixels in following frames; compositing can still discard it.
-noexact	switch	on	Allow following frames to zero RGB under transparent pixels (the default).

gif2webp parameter reference

Complete gif2webp 1.6.0 options and defaults

Parameter and aliases	Type / accepted values	Default	Meaning and limits
-o	path	none (encode without saving)	Output WebP file; - writes to stdout.
-lossy	switch	off	Encode lossy instead of the default lossless.
-mixed	switch	off	Pick lossy or lossless per frame automatically.
-near_lossless	integer 0–100	100 (no preprocessing)	Near-lossless preprocessing 0–100 for lossless frames; 100 is off.
-sharp_yuv	switch	off	Slower RGB-to-YUV conversion with better edges, for lossy frames.
-q	float 0–100	75	Lossy quality 0–100, or lossless effort.
-m	integer 0–6	4	Speed/size trade-off 0–6; 6 is slowest and smallest.
-min_size	switch	off	Spend more time to minimize size; disables inserted keyframes.
-kmin	integer	9 lossless; 3 lossy/mixed	Minimum frames between keyframes; libwebp may adjust inconsistent kmin/kmax pairs.
-kmax	integer	17 lossless; 5 lossy/mixed	Maximum frames between keyframes; 1 makes every frame a keyframe, 0 or less disables inserted ones.
-f	integer 0–100	60	Loop-filter strength 0–100 for lossy frames.
-metadata	comma-separated tokens	xmp	Copy ICC and XMP from the GIF: all, none, icc, xmp (comma-separated).
-loop_compatibility	switch	off	Legacy loop-count handling for Chrome 62 and earlier; skips the GIF-to-WebP count adjustment.
-mt	switch	off	Use multithreading where available.
-v	switch	off	Print conversion and mux diagnostics.
-quiet	switch	off	Print nothing.
-h, -help	action	not requested	Print help.
-version	action	not requested	Print encoder, mux and libsharpyuv versions, then exit.
--	action	not requested	Treat the next argument as the input GIF and stop parsing options.