WEBP and the alpha channel: what survives
Only one output format in this toolkit keeps transparency: PNG. Convert a transparent WEBP to anything else and the empty pixels get filled with a colour you choose — which is either exactly what you wanted, or the one thing worth checking first.
WEBP is not one format. It is a container that holds either a lossy picture, a lossless one, or an animation — and any of those can carry transparency. That flexibility is why a WEBP can sit in a web page at a quarter of the PNG's weight and still show a cut-out logo cleanly. When a program refuses to open it, the problem is support, not the picture.
What the converter does, in order
- The file is decoded in your browser tab, at its full resolution.
- The decoded picture is drawn onto a canvas at the size you asked for.
- For every target format except PNG, the canvas is filled with a background colour before the picture lands on it.
- The result is encoded again — as PNG without quality settings, as JPEG or WEBP at the quality level on the slider.
- The file is written to your downloads; nothing is uploaded at any point.
The background fill is the part worth reading twice. It happens for JPEG, for WEBP and for every other lossy target, because the canvas cannot hold transparency once the format cannot store it. The default is white; the colour picker next to the quality slider changes it. If your WEBP has soft, semi-transparent edges — a drop shadow, a hand-drawn outline — those pixels are blended with the background rather than thrown away, so a dark background can make a light logo look like it has a fringe.
Two conversions, two different jobs
| Conversion | What it is for | What happens to transparency |
|---|---|---|
| WEBP to PNG | Open the file in software that never learned WEBP | Kept — PNG stores alpha. |
| WEBP to JPG | A smaller file for a place that only accepts JPEG | Flattened onto the background colour. |
| JPG to WEBP | Shrink a photo for the web | JPEG has no transparency, so there is none to keep. |
A counter-intuitive consequence: converting a transparent PNG to WEBP in this tool also flattens it, even though the WEBP format can carry transparency. The canvas is prepared the same way for every non-PNG target, so the safe rule is simple — if transparency matters, end at PNG.
Quality, and why the default moves
JPEG and lossy WEBP are encoded at a quality level taken from the slider, which starts at 92. That is a sensible middle: high enough that artefacts stay invisible on photographs, low enough to shrink a file noticeably. PNG is encoded without a quality setting, because PNG is lossless by definition — the slider has no effect on it, and neither does the background colour.
Since every conversion re-encodes the picture, quality can only be lost, never gained. Converting JPEG to WEBP at quality 92 keeps the visible result indistinguishable in most cases; converting WEBP to JPEG at the same setting adds one more generation to whatever the file already carried.
The limits
- 64 MB per file, checked before the file is decoded.
- Output sides may not exceed 20,000 px.
- Resizing can go from 1% to 400% of the original, or to an exact size.
- Up to twenty files can be queued in one pass.
- Metadata is not copied into the new file: the output is the freshly encoded picture.
The short version
- PNG is the only target that keeps transparency; everything else is flattened.
- The background colour picker decides what transparent pixels become — white by default.
- Quality starts at 92 for lossy targets and does nothing for PNG.
- The conversion happens in your tab; the file is never uploaded.
Questions
Will my transparent WEBP stay transparent?
Only if the output is PNG. For JPEG and WEBP targets the canvas is filled with the background colour first, so transparent pixels are blended into it before encoding.
Why is the PNG larger than the WEBP?
Because WEBP compresses, with or without loss, and PNG stores every decoded pixel losslessly. A photograph converted to PNG is often several times larger.
Does the quality slider affect PNG output?
No. PNG is lossless by definition, so the converter encodes it without a quality setting; the slider only applies to JPEG and lossy WEBP.