A PNG to JPG conversion can’t keep a transparent background. JPEG has no alpha channel, so every clear pixel has to become some solid colour, and in our PNG to JPG converter that colour is pure white (255, 255, 255) unless you pick another one under Background. If the see-through part matters, the answer is a different format, and for a logo on a web page we think that format is WebP.
Which image formats support transparency
Three of the five common web formats can store a proper alpha channel, meaning an opacity value for every pixel. GIF can only switch one colour off. JPEG can’t do either.
| Format | Transparency | What that means for a logo |
|---|---|---|
| JPEG | None. MDN: “JPEG does not support an alpha channel.” | Clear areas are filled with a solid colour on save |
| GIF | One palette colour can be marked transparent; those pixels are fully clear, every other pixel fully solid | Soft, antialiased edges have to snap to on or off, which is where the jagged outline comes from |
| PNG | Full alpha, in greyscale and true colour modes | Edges and shadows keep their partial opacity |
| WebP | Full alpha, in both lossy and lossless files | Same as PNG, in a much smaller file |
| AVIF | Full alpha | Same again; the smallest file in our test |
One logo, five outputs
We ran the same file through our tools on 23 September 2026: a 960 by 300 pixel logo on a transparent background. Of its 288,000 pixels, 238,366 were fully clear and 7,789 were partly clear, the soft rim around each letter. Everything else was solid colour.
| Output | Setting | Bytes | Share of the original | Top-left pixel, fully clear in the source |
|---|---|---|---|---|
| PNG, repacked | Lossless | 20,733 | 71.8% | Still clear |
| JPG | Quality 90 (the converter’s default) | 20,972 | 72.6% | White, 255, 255, 255 |
| WebP | Quality 85 (the converter’s default) | 9,196 | 31.9% | Still clear |
| WebP | Quality 75 | 7,770 | 26.9% | Still clear |
| AVIF | Slider 75 | 5,304 | 18.4% | Still clear |
The JPG came out 239 bytes larger than the same logo repacked as a lossless PNG, so the conversion gave up the transparency and saved nothing.
JPEG is built for photographs, where smooth gradients hide its compression. A logo is mostly flat colour and sharp edges, which PNG already handles well. The 7,789 edge pixels are where the damage shows. Flattening blends each one with the fill colour in proportion to how see-through it was, so the rim of every letter is mixed with white. Put that JPG on a dark page and you get a white rectangle around the logo, and even if you crop the rectangle away, a pale fringe stays on the letters.
Google’s WebP page says lossy WebP with transparency is “typically” three times smaller than PNG. On our logo that held against the file as we received it (28,868 bytes down to 9,196, a factor of 3.1), but against the repacked PNG the factor was 2.3. Which PNG you compare with decides whether the claim looks right.
Our WebP encoder stores the alpha plane at full quality even when the colour is lossy, so the edge opacities are kept rather than approximated. We can’t say the same about AVIF with confidence. Our quality scores were computed after compositing every output on white, which hides edge errors instead of exposing them, and we haven’t yet looked at the AVIF version on a dark background at 200% zoom. One figure we didn’t test at all. Google says lossless WebP carries transparency “at a cost of just 22% additional bytes”, and our tool makes lossless WebP when the quality slider is at 100. We didn’t save the logo that way, so we have no number of our own to set against it.
Formats and sizes for photos, where the ranking changes, are in our AVIF, WebP and JPG measurements.
For logos on a website, use WebP at 85
AVIF was smaller: 5,304 bytes against 9,196. The difference, 3,892 bytes, is less than the 4 KiB Lighthouse uses as its threshold before it calls a JPEG worth re-compressing, and a logo usually loads once and then sits in the cache. We’d give up those few kilobytes for the older format: we run an AVIF to JPG converter because some apps and upload forms still refuse AVIF. Keep the original PNG as your master copy and convert it to WebP for the site.
That advice is wrong in two places. If your logo exists as a vector file, serve the SVG instead; it stays sharp at every size, and we don’t make SVGs. And if the image is going into an email signature or an app that won’t take WebP, send the PNG; WebP to PNG gets you back there with the transparency intact.
When you do want a JPG
Some places only take JPG. Then choose the fill instead of accepting white: the Background control in our tools has white, black and a colour picker, so you can match the page or slide the logo will sit on. Some other converters offer the same choice. Match it exactly and the fringe disappears into the background, because the edge pixels get blended with the colour that will surround them anyway.
GIF is the other old option, and our tools can write it. The transparency is one palette entry, on or off, so those 7,789 soft edge pixels get forced to fully clear or fully solid. On a white page you may not notice. On anything darker you will.