See how a specific image responds to different WebP quality values instead of relying on a generic recommendation. The tester performs five genuine local encodes, then records exact output bytes, percentage of the original, and elapsed encoding time for every sample.
How to use Quality vs Size Tester
- Add one or more static WebP files; animated files are rejected instead of being silently flattened.
- Choose a broad, web-focused, or high-quality sampling range and start the test.
- Compare the JSON rows, preview likely quality choices separately, and use the measurements to choose a deliberate production setting.
What this tool is good at
When to use Quality vs Size Tester
Prepare a deliberate quality comparison asset
Use five completed WebP encodes to choose a practical quality range for one real image rather than copying a quality number from an unrelated asset. Work from the selected WebP's decoded pixels and measured output instead of assuming a filename, generic preset, or browser preview answers the production question.
Compare real local results
Compare exact bytes, source-size ratios, and elapsed encoding time, then perform a visual review at the intended display size before publishing. Keep the derivative or JSON report with a content ticket, optimization review, design handoff, or regression fixture so another person can reproduce the decision.
Protect private production imagery
Process unreleased campaigns, product photos, client media, interface assets, and internal fixtures in the current browser tab without submitting selected image bytes to a remote conversion or analysis endpoint.
How to choose the right settings
Match the destination requirement
Use five completed WebP encodes to choose a practical quality range for one real image rather than copying a quality number from an unrelated asset. Confirm dimensions, background, alpha behavior, quality budget, analytical resolution, and consuming application before applying the same setting to a larger batch.
Inspect a representative result
Compare exact bytes, source-size ratios, and elapsed encoding time, then perform a visual review at the intended display size before publishing. Check detailed and flat-color samples, transparent edges, gradients, text, and varied aspect ratios because one convenient default cannot represent every source.
Retain the authoritative original
Canvas quality is an encoder hint rather than a portable standard, animation is rejected, metadata is not present in test derivatives, and the report does not calculate perceptual similarity. Keep source WebP files until generated assets and reports have been reviewed in the real destination and accepted by the responsible editor or developer.
Practical workflow and output details
The browser decodes one static source, encodes fixed quality samples sequentially, measures Blob sizes and elapsed time, and writes a structured report. Processing uses bounded browser Canvas operations, typed-array pixel analysis, local WebP or PNG encoding, and Blob downloads; selected file bytes are never posted for image processing.
Canvas quality is an encoder hint rather than a portable standard, animation is rejected, metadata is not present in test derivatives, and the report does not calculate perceptual similarity. The tool states this boundary so a focused local operation is not mistaken for a color-managed editing suite, universal performance benchmark, perceptual-quality guarantee, animation editor, or reversible source-of-truth workflow.
Format behavior and limitations
Canvas quality is a browser encoder hint, not a standardized visual score, so values from another codec are not directly equivalent.
The report measures compressed bytes and timing but does not replace visual review or a perceptual metric such as SSIM.
Frequently asked questions
Does this estimate file size?
No. Every row comes from a completed WebP encode in the current browser.
Which quality should I choose?
Choose the smallest result that still looks acceptable at its actual display size; photographic detail, gradients, and text react differently.
Why can results differ between browsers?
Browsers may use different encoder versions and hardware, so compare production decisions in the environment that matters.
Related WebP tools
Compression Savings
Re-encode WebP at a selected quality and calculate genuine bytes saved, percentage change, and whether the result is smaller.
WebP Quality Changer
Re-encode static WebP images at a deliberate quality level and compare genuine output size before downloading.
WebP PSNR Calculator
Re-encode a static WebP at a selected quality and calculate genuine RGB PSNR against its decoded source pixels.