PNG, JPEG or HEIC: picking a format
One of these is lossless, one degrades every time you save it, and one is half the size but will confuse the person you send it to. The right choice is almost entirely determined by what the image contains.
Most people pick an image format by habit, and the habit is usually JPEG. That is right about half the time and visibly wrong the other half.
The decision is not complicated once you know what each format is built for.
JPEG
Lossy. It throws away information the eye is unlikely to notice, and achieves large size reductions doing it. Designed for photographs — continuous gradients, soft transitions, natural detail.
Where it fails is hard edges. Text, line art, screenshots and flat colour develop visible artefacts: a faint halo of noise around every letter, blotches in areas that should be one solid colour. Once you know what JPEG artefacts look like you cannot stop seeing them on badly chosen files.
The other property people underestimate: re-saving degrades it further, every time. Open a JPEG, change nothing, save — it is now slightly worse. Do that six times and the difference is obvious. Never use JPEG as a working format; use it as a final output.
No transparency support.
PNG
Lossless. What goes in comes out, exactly. Supports transparency, including partial transparency for soft edges.
Correct for: screenshots, diagrams, logos, illustrations, anything with text, anything with flat areas of colour, anything that needs a transparent background.
The cost is size. A photograph saved as PNG can easily be five to ten times larger than the JPEG equivalent at indistinguishable quality. PNG compresses repeated patterns and flat colour brilliantly and photographic noise barely at all.
HEIC
What your iPhone shoots by default. Roughly half the file size of JPEG at comparable quality — genuinely better compression, and it supports transparency and higher bit depths.
The problem is entirely about who receives it. Support is good across recent Apple devices and Windows 11 with an extension installed; it is patchy everywhere else. Send a HEIC to someone on an older Android phone or an unfamiliar Windows machine and there is a real chance they cannot open it.
Excellent for storage on your own devices. Risky as something you send.
The decision, compressed
| What it is | Use |
|---|---|
| Photograph, for the web or email | JPEG |
| Screenshot | PNG |
| Logo, icon, anything with transparency | PNG |
| Diagram, chart, anything with text | PNG |
| Photograph stored on your own devices | HEIC |
| Anything you are sending to someone unknown | JPEG or PNG |
| A working file you will edit again | Neither — keep the project file |
The most common mistake, by a distance: saving a screenshot as JPEG. The text goes fuzzy, artefacts appear around every character, and the file is frequently not much smaller than the PNG would have been. Screenshots are flat colour and hard edges — the exact case JPEG handles worst.
The second most common: sending a 12MB PNG of a photograph because "PNG is higher quality". It is lossless, which is not the same as necessary. Nobody can see the difference at web sizes.
Converting on a Mac
Preview handles it: open the image, File → Export…, pick from the Format dropdown. Hold Option while opening that dropdown to reveal additional formats.
For several files at once, select them in Finder, open together in Preview, select all in the sidebar, then Export — it applies to everything selected.
Two things to watch when converting:
Converting JPEG to PNG does not restore quality. The artefacts are already in the pixels. You get a larger, lossless copy of a degraded image.
Converting anything to JPEG is a one-way door. Keep the original.
The quality slider
When exporting JPEG you get a quality slider. The useful range is narrower than it looks: somewhere around 80% is typically indistinguishable from maximum at a fraction of the size. Above 90% you pay a lot of bytes for nothing visible. Below about 60% the artefacts become obvious on detailed images.
If the file needs to hit a specific size, reducing dimensions is usually better than pushing quality down — a smaller image at good quality looks better than a large one at bad quality.
Doing this in Miyu Paint
Miyu Paint's free tools export PNG and JPEG up to 2048 pixels on the longest edge, without a watermark — which covers the whole of this article for screen use. Opening, cropping, resizing and drawing are free too.
Full access adds advanced formats, export at full resolution, printing, and the layer system — pixel, text, shape, group, mask and adjustment layers — plus editable .mpaint project files. That last one is the answer to the last row of the table above: the working file you keep, from which you export whichever flat format the job needs.
The trial is fourteen days, you start it yourself, and it does not renew into a charge. Document processing happens on your Mac — no account, no advertising, no analytics.