Converting is not renaming
Changing a file's extension from .png to .jpg does not make it a JPEG. It makes it a PNG that many programs will refuse to open, because the bytes inside still say PNG.
The [msm_tool slug="image-converter"] redraws the image and re-encodes it in the format you choose, which produces a genuine file of that type. That distinction sounds obvious and it accounts for a steady stream of "this image is corrupted" reports.
Choosing a format
- JPEG — photographs. It discards detail the eye is poor at noticing, which suits continuous tone and ruins flat colour with sharp edges. No transparency.
- PNG — graphics, logos, screenshots, anything with text or hard edges. Lossless and supports transparency, at the cost of considerable size on photographs.
- WebP — the safe modern default. Smaller than both at comparable quality, supports transparency, and works in every current browser. If you are choosing for the web and have no specific reason otherwise, this is the answer.
- AVIF — smaller again, and not every browser can create it.
Why AVIF sometimes refuses
Chrome and Edge can encode AVIF. Firefox and Safari can display it but cannot produce it, because the encoder is not in the browser.
That matters because a canvas asked for a format it cannot encode quietly returns a PNG instead. Without a check you would be handed a PNG named with an AVIF extension — the renaming problem again, arrived at by accident. The tool asks the browser first and tells you plainly rather than letting it fall back silently.
If you need AVIF and your browser will not produce it, use Chrome or Edge for that one conversion.
Converting to PNG does not restore a JPEG
This is the most persistent misunderstanding about image formats.
PNG is lossless, which means it stores exactly what it is given. Given a JPEG that has already discarded detail and acquired compression artefacts, it stores those artefacts perfectly, in a file several times larger. The image is not improved; it is preserved as-is at greater cost.
Lost detail is lost. The only way to get a clean PNG is to start from something that was never a JPEG.
Transparency and the white background
JPEG has no alpha channel, so a transparent image converted to JPEG must have its transparency resolved to something. The tool flattens onto white first.
White because the alternative — what happens if you do nothing — is black, and a logo that was transparent arriving with a black box around it is almost never what anyone wanted. If you need a different background colour, composite it before converting.
The quality setting
It applies to the lossy formats only: JPEG, WebP and AVIF. PNG ignores it entirely, because there is nothing to trade.
Most photographs sit well between 80 and 90. Below about 80 the artefacts become visible in flat areas — skies and skin are where they show first. Above 90 the file grows quickly for a difference almost nobody can see.
One thing worth knowing: every re-encode of a lossy format compounds. Converting a JPEG to WebP and back to JPEG twice produces visible degradation even at high quality settings. Convert from the best original you have, once.
A practical workflow
- Keep the original in whatever format it came in.
- Resize to the dimensions you actually need first.
- Convert to WebP at 80–85 as the last step.
- Keep a JPEG fallback only if you support browsers that need one, which by now is very few.
Doing the resize before the conversion means one lossy encode rather than two, and the difference is visible on detailed images.
Nothing is uploaded
The conversion happens in your browser, which is worth knowing if the image is a screenshot of something confidential or a photograph you would rather not hand to a service in exchange for a smaller file.