You save a screenshot of a spreadsheet as a JPG, and every number comes out with a faint grey haze around it. Or you export a holiday photo as a PNG to "keep the quality," and the file is suddenly several megabytes and won't attach to an email. Both come from the same mistake: picking PNG or JPG by reputation instead of by what the image actually contains.
The short answer
Photos → JPG. Screenshots, text, logos and anything with transparency → PNG. When you're not sure, save both and compare the file size and how the edges look.
| If the image is… | Use | Because |
|---|---|---|
| Photo (people, places, products) | JPG | Much smaller, and the loss is invisible at a sensible quality |
| Screenshot, chart, text, UI | PNG | Sharp text, and often a smaller file too |
| Logo or icon with a transparent background | PNG | JPG can't store transparency |
| Photo with text or graphics on top | JPG at high quality, or PNG if the text blurs | Check the text edges before deciding |
| Image you'll keep editing | PNG (as a working copy) | Re-saving a JPG loses a little more each time |
| Upload form that says "JPG only" | JPG | The form decides; convert, don't rename |
The actual difference between PNG and JPG
JPG is lossy. It's designed for photographs. It discards fine detail the eye is bad at noticing, especially subtle colour variation, and that's how it gets files so small. The quality setting controls how much it throws away.
PNG is lossless. Every pixel comes back exactly as it went in. It compresses by finding repetition: runs of the same colour, repeated patterns. That's very effective for a screenshot full of flat white space, and nearly useless for a photo where no two neighbouring pixels are quite alike.
That's the whole story in two lines. JPG is good at photographic content and bad at hard edges. PNG is good at flat, sharp-edged content and bad at photos. PNG also supports transparency; JPG doesn't.
For photos, use JPG
In IMAGE SIZE PRO's own format benchmark, a 1200×800 photo-like test image came to 1.4 MB as PNG and80 KB as a JPG at quality 80, about 18 times smaller. At that quality setting most people can't tell the two apart without zooming in.
This is why "save as PNG to keep the quality" backfires for photos. You keep detail nobody can see and pay for it in a file that's too big to upload, slow to load, and awkward to send. If a photo is already a JPG, keep it as one.
The benchmark uses synthetic test images and the sharp/libvips encoder, so your own photos will give different numbers. The direction (PNG much larger for photos) is consistent. Full method and limits are on thebenchmark page.
For screenshots, text and graphics, use PNG
This is where people get surprised. PNG isn't just sharper for flat graphics; it's usually smaller too. The same benchmark's flat-colour UI graphic (the kind of thing a screenshot or icon looks like) was15 KB as PNG and 78 KB as a JPG, roughly 5 times larger, and the JPG was the one with smudged edges.
JPG struggles with a sharp line between two flat colours, like black text on a white background. It leaves faint blocky "ringing" around every letter, which is the grey haze from the spreadsheet example. Charts, diagrams, UI mockups, scanned typed documents, pixel art and line drawings all fall in this category.
Logos and transparent backgrounds
A logo that needs to sit on different coloured backgrounds needs transparency, and JPG simply doesn't have it. Convert a transparent PNG to JPG and every see-through pixel has to become a solid colour. Depending on the software that's often black, sometimes white. Either way the "cut-out" look is gone.
So keep logos and icons as PNG. If you must produce a JPG (some forms insist), place the logo on the exact background colour it'll be shown on first, then convert, and check the result before you use it. For logos on a website, SVG is often better still: it's a vector format, so it stays sharp at any size.
The in-between cases
A photo with text on it
YouTube thumbnails, social posts, product shots with a price badge. The photo part wants JPG and the text part wants PNG. Usually a JPG at a high quality setting is the right trade: check the lettering at 100% zoom, and if you can see smudging around it, try PNG or WebP and compare the sizes.
A scanned document
A clean scan of printed text is closer to a screenshot, so use PNG. A scan of a photo, or a document with lots of paper texture and shading, behaves like a photo, so use JPG. If an application form asks for a scanned document under a size limit, JPG is usually the only way to get there.
An image you're still editing
Every time you open a JPG, change it and save it again, it goes through lossy compression again, and the damage builds up. Keep a PNG (or your editor's own format) as the working copy, and export a JPG once, at the end.
Converting between PNG and JPG
- PNG → JPG is a one-way step. You get a much smaller file for photos, lose transparency, and can't get the discarded detail back. Keep the PNG original.
- JPG → PNG doesn't undo anything. Existing JPG artifacts are preserved exactly and the file usually grows several times over. It's only worth doing if you'll keep editing, or a system requires PNG.
- Renaming isn't converting. Changing
.pngto.jpgleaves the file as a PNG inside. Some programs open it anyway, but upload forms that check the real format reject it.
The image format converter re-encodes the file properly in your browser without uploading it, and shows the new file size so you can see whether the switch was worth it.
What about WebP?
WebP does both jobs: a lossy mode for photos and a lossless mode for graphics, with transparency in either. In the same benchmark, the photo-like image came to 62 KB as WebP at quality 80 (against 80 KBfor JPG), and the flat graphic shrank to just 372 bytes as lossless WebP.
Current versions of all major browsers display WebP, so for images on your own website it's often the best choice. Outside the browser it's less certain: plenty of upload forms, email clients, older editing software and print shops still expect JPG or PNG. Use WebP where you control how the image is shown, and JPG or PNG where someone else's system has to accept it.
Quick guidance by destination
- Your website: WebP where you can; otherwise JPG for photos and PNG for graphics. Size them to the space they fill. The format compression benchmark shows how much each format saves on real test images.
- Social media: the platforms re-compress uploads anyway. Upload a good-quality JPG for photos, and PNG for graphics with text if the text matters. See thesocial image size guide for dimensions.
- Application forms: use whatever the form lists, which is usually JPG, and watch the size limit. The guide to getting a photo under a KB limit covers that part.
- Email and messaging: JPG for photos keeps attachments small.
Before you save
- Is it a photo? JPG. Mostly flat colour, text or lines? PNG.
- Does it need a transparent background? PNG (or WebP).
- Look at text and sharp edges at 100% zoom after saving as JPG.
- Compare the two file sizes if you're unsure. The smaller one that looks right wins.
- Keep the original, especially before converting PNG → JPG.
If the right format still leaves the file too large, the next step is compression rather than a format switch.How image compression works explains the trade-off, and the image quality guide shows how to spot when you've pushed it too far.