Create a reusable alpha mask from the actual decoded transparency of a WebP. Continuous mode retains every opacity level in a white PNG, while binary mode converts the mask to fully transparent or fully opaque pixels at a chosen threshold.
How to use Alpha Mask Generator
- Select a static WebP whose transparency should become a standalone mask.
- Choose continuous alpha or binary threshold mode and set the cutoff when applicable.
- Generate the PNG, inspect edges against contrasting backgrounds, and use it in a compositor or graphics workflow that accepts alpha masks.
What this tool is good at
When to use Alpha Mask Generator
Prepare a deliberate alpha mask asset
Export decoded transparency for compositing, shader, texture, or graphics workflows as continuous alpha or a deliberate binary cutoff. 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
Test partial edges against light and dark backgrounds and keep the threshold value with any binary mask so the transformation can be reproduced. 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
Export decoded transparency for compositing, shader, texture, or graphics workflows as continuous alpha or a deliberate binary cutoff. 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
Test partial edges against light and dark backgrounds and keep the threshold value with any binary mask so the transformation can be reproduced. 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
Binary conversion removes intermediate opacity, the result is not an editable vector path, color metadata is omitted, and animated alpha sequences are outside this static workflow. 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
Decoded alpha bytes are copied into a white PNG mask or thresholded to zero and 255 without using source RGB colors. 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.
Binary conversion removes intermediate opacity, the result is not an editable vector path, color metadata is omitted, and animated alpha sequences are outside this static workflow. 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
The output uses white RGB values and stores the mask in PNG alpha; software that expects grayscale RGB should use Extract WebP Alpha Channel instead.
Binary thresholding permanently removes partial edge opacity and can create jagged outlines when the cutoff is unsuitable.
Frequently asked questions
Why is the mask white?
White color makes the alpha itself easy to reuse while avoiding source colors in the mask asset.
What does threshold 128 mean?
In binary mode, source alpha values at or above 128 become opaque and lower values become transparent.
Does continuous mode change alpha?
No. Each decoded source alpha byte is copied into the PNG mask's alpha channel.
Related WebP tools
Extract Alpha Channel
Extract decoded WebP opacity into an opaque grayscale PNG where black is transparent and white is opaque.
Fill Alpha Channel
Replace every decoded pixel alpha value with one selected opacity while retaining RGB color and image dimensions.
WebP Transparency Checker
Decode every WebP frame and count actual transparent or translucent pixels instead of relying only on an alpha feature flag.