PNG or JPG? Pick by What's in the Image, Not by Habit

A screenshot saved as JPG is bigger AND uglier than the same screenshot as PNG. A photo saved as PNG is ten times larger for nothing. The format decision is about image content - here's the whole logic with real numbers.

D

Derek

Author

Save a screenshot of a spreadsheet as JPG and you get fuzzy text in a file that's larger than the PNG would have been. Save a beach photo as PNG and you get a 20 MB monster that looks exactly like the 2 MB JPG. Both mistakes happen constantly, and both come from treating the format choice as a habit instead of a decision.

The decision is genuinely simple once you know what each format is good at compressing.

The one-sentence rule

Photographs go in JPG. Screenshots, text, logos, and anything with flat colors goes in PNG.

That covers 95% of cases. The rest of this article is the why, the numbers, and the exceptions.

Two formats, two completely different ideas

JPG compresses by analysing frequency patterns and throwing away detail your eye is bad at noticing. That works brilliantly on the smooth gradients of a photograph - skies, skin, shadows - which is why a 12-megapixel photo lands around 2-4 MB as a quality-85 JPG but balloons to 15-25 MB as PNG.

But hard edges are exactly what JPG's math handles worst. Text, window borders, and single-pixel lines come out with a faint shimmer of artifacts around them - you've seen it on screenshots that look like they were photographed through a dirty window.

PNG compresses losslessly by finding repeated patterns. Flat interface colors and repeated pixels compress beautifully: a 1080p screenshot of a code editor is typically 150-400 KB as PNG and would be both larger AND blurrier as JPG. Point a PNG at a photograph, though, and there are no repeated patterns to find - sensor noise defeats it - so the file grows enormous while gaining nothing visible.

Transparency is the tiebreaker

PNG supports an alpha channel; JPG doesn't. Convert a logo with a transparent background to JPG and the transparency gets filled - usually white, sometimes black - which is why logos on colored website backgrounds sometimes sit inside an ugly white box. If any part of the image needs to be see-through, the decision is made for you: PNG (or SVG, if it's vector art to begin with).

The mistakes that actually cost quality

Re-saving JPGs over and over. Every save re-runs the lossy compression. One save is invisible; ten rounds of open-edit-save visibly muddy the image. If a JPG needs several editing sessions, convert it to PNG first, do all the editing losslessly, and export a JPG once at the end. That's the legitimate reason to turn a JPG into a PNG - not to gain quality (impossible), but to stop losing more.

PNG photos on web pages. A hero image as PNG can be 10x the weight of the visually identical JPG, and page speed metrics eat the difference. If a site feels slow and its photos are PNGs, that's often the whole diagnosis. You can convert PNG photos to JPG in batches and typically drop 80-90% of the image weight without a visible change.

Converting JPG to PNG expecting improvement. The artifacts are baked in. PNG faithfully - losslessly - preserves them in a much bigger file. No format conversion recovers detail that compression already discarded.

Quality settings worth memorising

For JPG exports, 80-85 is the sweet spot - visually transparent for almost everything, roughly a third the size of quality-100. Above 90 you pay a lot of bytes for differences you need a loupe to find. Below 70, artifacts show on anything with detail. And quality-100 JPG is still lossy; it's not a PNG substitute, just an expensive JPG.

Where WebP and HEIC fit

Both beat the classics on pure compression - WebP runs 25-35% smaller than equivalent JPG and handles transparency too. The catch is the long tail: government upload portals, older office software, embedded systems, and some email clients still reject or mangle them. My working rule: WebP for images I control on my own website, JPG/PNG for anything leaving my hands - attachments, uploads, documents. An image that fails to open costs more than the kilobytes it saved.