PNG is lossless and often much bigger than it needs to be for a photo. Converting to JPG trades some of that losslessness for a meaningfully smaller file — the right call for photographs headed to the web or an inbox, less so for graphics with sharp edges or transparency.
Transparency doesn't survive the conversion
JPG has no alpha channel. Any transparent pixels in the source PNG lose their transparency and keep only their underlying color — commonly black, since that's what most tools store under a transparent area by default. If that matters for your image, flatten it onto your intended background first, or keep it as PNG.
FAQ
What happens to transparency?
JPG has no alpha channel, so it can't be carried over. The transparent areas of your PNG aren't filled in with white — the alpha channel is simply dropped and whatever color was stored underneath it is what's left. Most PNGs with transparent backgrounds store black there by default, so that's usually what you'll see. If you need the transparent areas to end up white (or any specific color), flatten the PNG onto that background before converting, or keep it as PNG.
Will the JPG look worse than the PNG?
For anything that isn't a photograph, likely yes at close inspection. JPG's lossy compression handles smooth photographic gradients well but can introduce visible artifacts around sharp edges, text, and flat color blocks — exactly what a lot of PNGs contain (screenshots, logos, graphics). At normal viewing sizes it's often not noticeable, but it's a real quality tradeoff, not a neutral repack.
Why convert PNG to JPG at all?
File size, mainly. PNG is lossless and doesn't compress photographic content efficiently, so photos saved as PNG are often several times larger than they need to be. Converting to JPG is the standard move for shrinking photos meant for the web, email, or anywhere upload size limits matter.
Is this a good idea for logos or screenshots?
Usually not. Flat colors and sharp edges are exactly what JPG compresses worst, and if the image has any transparency you'll lose it. PNG (or WebP) is the better format for that kind of content — this conversion is best reserved for actual photographs.
Need to go back the other way, losslessly? Try JPG to PNG.
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