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 happen inside this page, so the image is never uploaded anywhere.

How it is calculated

canvas.toBlob(callback, "image/jpeg", quality)

The image is drawn onto a canvas and re-encoded by the browser itself. Quality is a number between 0 and 1 for lossy formats, so the percentage you pick is divided by a hundred before it is passed on.

Source: MDN HTMLCanvasElement.toBlob() — quality is a number between 0 and 1 for lossy formats

Questions people ask

What happens to transparent areas?

JPEG has no alpha channel, so transparency cannot survive the conversion. Rather than letting the browser 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?

The limit is your device rather than our server, because there is no server involved. Very large images use memory proportional to width times height, so a phone will give up sooner than a desktop.

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