Lossless vs Lossy WebP: Real Photo Test
Lossless WebP preserved the decoded RGB pixels exactly in this run: SSIM was 1.0 and both RGB SHA-256 hashes matched. It was 13,831,752 bytes. The matched lossy WebP file was 2,224,544 bytes at SSIM 0.960073. Lossless protects the decoded pixels but cannot restore detail already removed by the original JPEG.
Short answer
Lossless WebP kept the decoded pixels exactly (SSIM 1.0) at 13,831,752 bytes, against 2,224,544 bytes for matched lossy WebP at SSIM 0.960073. Use lossy for photos and lossless WebP for graphics with text and edges.
Measured data
The image run used a NASA public-domain photograph, 3.1 MB, decoded once to a fixed RGB reference. Results describe this photograph and these exact encoder settings.
| Mode | Setting | Bytes | SSIM vs decoded RGB reference |
|---|---|---|---|
| WebP lossy | quality 85, compression level 6 | 2,224,544 | 0.960073 |
| WebP lossless | lossless 1, bgra | 13,831,752 | 1.0 |
The lossless encode and decoded RGB reference produced the same SHA-256: 81404aac832f86468974470a56f031d58cce8d4b94c7d0868be3c3cd79c9c364.
The fixed RGB reference prevents a YUV conversion from being counted as loss. Lossless arguments: `-c:v libwebp -lossless 1 -pix_fmt bgra`; lossy arguments: `-c:v libwebp -q:v 85 -compression_level 6`.
When to use each option
Use lossless for pixel preservation
Choose it when the exact decoded pixels, hard edges or repeated editing matter more than download size.
Use lossy for delivery size
Choose a measured setting for photographs when smaller transfer size matters and inspect the result at the final display size.
Keep the original JPEG too
Lossless WebP preserves the pixels decoded from the JPEG. It does not recover information discarded when that JPEG was first created.
Questions people ask
Why is lossless WebP larger than the source JPEG?
The JPEG is already lossy and compact. Lossless WebP preserves every decoded pixel, including compression artifacts, so it can be much larger.
Was the lossless result really identical?
Yes for decoded RGB pixels in this run: SSIM 1.0 and matching SHA-256 hashes.
Does lossless restore JPEG detail?
No. It prevents additional pixel loss after decoding but cannot reconstruct information absent from the JPEG.
Which photograph did this page measure?
A NASA public-domain photograph, 3.1 MB, decoded once to a fixed RGB reference.
Measured vs sourced
Cells marked measured are Koldflux Media Lab measurements. Cells marked sourced derive from each platform / codec standards body. Cells marked guidance are expert guidance, not measured.
Sources
- Google WebP compression documentation (read 2026-10-08)
- NASA image record: Buzz Aldrin salutes the U.S. flag (read 2026-10-08)
- FFmpeg codec documentation (read 2026-10-08)
Verified at 2026-10-08.
Next steps
Inspect my file: /tools/validate
Convert / make correct version: /tools/convert
Create all target versions: /tools/pack