PNG to JPG

PNG stores every pixel exactly and can be transparent; JPG throws away detail the eye is unlikely to miss and cannot be transparent at all. That trade is why a photograph saved as PNG is often several times larger than it needs to be, and why converting it to JPG is usually the fastest way to shrink it. Both the decoding and the encoding are done by libvips on our server, which is what lets the same page also take a TIFF or an animated GIF that a browser would refuse to open.

How it is calculated

sharp(file).rotate().resize(width).jpeg({ quality, mozjpeg: true })

libvips decodes the image, applies the orientation the camera recorded, redraws it at the requested width and re-encodes it. Quality is an integer from 1 to 100, and the mozjpeg settings squeeze a JPEG smaller at the same visual quality than a plain encoder would.

Source: sharp output options — jpeg() and webp() take "quality, integer 1-100" (default 80), avif() defaults to 50, and mozjpeg means "use mozjpeg defaults, equivalent to { trellisQuantisation: true, overshootDeringing: true, optimiseScans: true, quantisationTable: 3 }"

Questions people ask

What happens to transparent areas?

JPEG has no alpha channel, so transparency cannot survive the conversion. Rather than letting the encoder decide — which usually produces black — this converter fills transparent pixels with the background colour you choose, white by default.

Will converting back to PNG restore the quality?

No. JPEG compression is lossy: the discarded detail is gone for good. Converting the JPG back to PNG gives you a larger file of the same degraded image, so keep the original PNG if you may need it later.

Why is my JPG bigger than the PNG?

It happens with flat graphics — logos, screenshots of text, line art. PNG compresses large areas of identical colour extremely well, while JPEG is tuned for photographs and adds artefacts around sharp edges. For that kind of image, keep the PNG or try WebP.

Is there a file size limit?

A single file may be up to 30 MB, and there is a cap on how much one address may convert in five minutes so that the converter stays free for everyone. Very large images use memory proportional to width times height, so a phone will give up sooner than a desktop.

Can I convert several files at once?

Yes. Drop in as many images as you like and every one of them comes out as JPEG. They may be different formats — PNG, JPEG, WebP, GIF, BMP, AVIF, TIFF, SVG, ICO can sit in the same list — because each file is converted on its own. Download them one by one, or take the whole batch as a single .zip.

What if I want PNG or WebP or GIF or AVIF or TIFF instead of JPEG?

Pick it under "Convert to". This page opens on JPEG because that is the conversion it is named after, but PNG and WebP and GIF and AVIF and TIFF are one click away, and the options underneath follow whichever you choose — quality appears for the formats that are lossy, a background colour for the ones that cannot store transparency.

Sources

The documents this page reads its numbers out of, linked so you can check them yourself.

1. sharp output options — jpeg() and webp() take "quality, integer 1-100" (default 80), avif() defaults to 50, and mozjpeg means "use mozjpeg defaults, equivalent to { trellisQuantisation: true, overshootDeringing: true, optimiseScans: true, quantisationTable: 3 }"
2. MDN image file type guide — JPEG is image/jpeg with extension .jpg and no alpha channel

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