App Store Screenshots: PNG or JPG

Flat colour, sharp text and gradients. All three are where JPEG shows its working.

I compared the two stores' accepted formats before writing this, because people assume one of them forces JPEG and neither does.

Apple's screenshot specification lists .jpeg, .jpg and .png, and bans alpha channels and transparency.

Google's asset requirements ask for JPEG or 24 bit PNG, again with no alpha.

So the format is genuinely your choice on both.

The transparency rule is not. That one is identical and absolute.

So any advice that tells you a store demands one format is out of date or wrong. Check the specification rather than a forum post.

JPEG was designed for photographs, where small errors hide in natural detail.

A screenshot is the opposite. Hard edges between two flat colours, white text on a solid background, a logo with clean corners.

JPEG stores those badly and the damage shows up exactly where the eye is already looking.

PNG stores every pixel as it was. That's the whole argument, and it's enough.

The irony is that JPEG was a genuinely brilliant piece of engineering for the job it was built for.

This is not that job.

A screenshot of a screenshot compounds it. Compress once at export and never again.

Three things, and once you know them you can't unsee them.

A faint halo around white text on a coloured background. Blocky patches in a smooth gradient. Slightly muddied edges on a logo.

At full size on a monitor you might miss it. Scaled into a search result it reads as cheap.

And it's permanent, because a lossy export cannot be undone.

The halo is the one that matters most, because it sits on your caption.

A caption with a faint grey fringe reads as slightly out of focus, and nobody can say why.

JPEG stores colour at lower resolution than brightness, a trick called chroma subsampling.

That's fine on a photograph of a face. It's not fine on saturated brand colour meeting white text.

Red text on a dark background is the worst case and it's a common design choice.

PNG has no equivalent step, so the colour edge stays exactly where you put it.

Blue on orange and green on magenta do the same thing. Any pair far apart in hue and close in brightness will show it.

PNG files are bigger. That's the only real cost.

A full size screenshot might be a few hundred kilobytes as JPEG and a couple of megabytes as PNG.

You upload these once, and the store serves compressed versions to users anyway.

So you are not saving your users anything. You are saving yourself thirty seconds of upload.

A whole set of ten screenshots as PNG is perhaps twenty megabytes. That is one upload, once, on a connection that handles video calls.

Rarely, and worth knowing.

Google documents a file size cap for the app icon at 1,024 KB, and does not publish one for screenshots on the same page.

I read both stores' asset pages for a screenshot cap and found one only for the icon. So if an upload fails and the dimensions are right, check the size before assuming something stranger.

Dropping from PNG to a high quality JPEG is the fix at that point, not a lower resolution.

A high quality JPEG of a mostly flat design is still small. You lose less than you would by cutting the resolution.

Eight bits each for red, green and blue. Sixteen million colours, no transparency.

The alternative is 32 bit, which adds an alpha channel, and that's the one both stores reject.

Some design tools export 32 bit by default even when nothing in the image is transparent.

That's why a completely opaque looking screenshot can still fail at upload for transparency.

The fix is a checkbox in the export dialog, usually labelled transparency or alpha. Uncheck it.

The commonest upload failure, and the most annoying, because the image looks perfect.

A rounded device corner, a soft drop shadow, a layer left at 99 percent opacity. Any of those leaves an alpha channel behind.

The fix is to flatten onto a solid background before export, not to delete the shadow.

We covered the rest of the upload level failures in the screenshot rejection post.

If your tool has no flatten option, place a solid colour rectangle on the bottom layer covering the whole canvas. Same result.

Worth separating out, because the names are confusingly close.

An 8 bit PNG uses a 256 colour palette. It's tiny and it destroys gradients.

Some export presets labelled PNG 8 will quietly do this to your background.

If your smooth background arrives at the store looking striped, that's what happened. Export 24 bit.

The preset is often named for the web, where the small file mattered. It does not matter here.

One case. A screenshot that is mostly photographic, with no overlaid text.

A photo editing app showing a real photograph, a travel app showing a landscape.

There, JPEG at high quality is genuinely hard to tell apart and much smaller.

Add a caption in white text over it and you're back to PNG.

Even then, export at the highest quality setting. The file will still be far smaller than the PNG.

The rule that saves more quality than the format choice.

Every JPEG save loses a little more. Open a JPEG, add a caption, save again, and you've compressed the whole image twice.

Keep the master in your design tool and export fresh every time.

Never edit an exported file and re save it. That's how a set degrades over three rounds of small fixes.

This applies to screenshots taken on a device too. A device screenshot is already a PNG, so keep it as one.

Captions are the highest value pixels in a screenshot set, and the ones compression hurts first.

They're also the part a person reads at thumbnail size, where any softness costs you.

So the format decision is really a caption decision.

Sizes and weights for that text sit in the caption readability post.

Everything else in the frame can lose a little and survive. The words cannot.

Zoom to 200 percent on one caption and one logo edge.

Look for a halo, a blocky patch, or colour bleeding past an edge.

Then check the file's bit depth, which every image tool shows in its info panel.

Twenty four bit, no alpha, dimensions correct. Three things, one minute.

Do it on the first and last image in the set. If those two are clean, the middle ones came out of the same export.

PNG, 24 bit, no interlacing, no alpha, sRGB colour.

Save that as a preset and stop thinking about it.

The dimensions change per device family. The format never does.

You can export a whole set at the right sizes from our editor without touching an export dialog.

Name the preset after the store. You will use it every release for years.

PNG at 24 bit for everything with text on it.

JPEG only for a photographic screenshot with no overlay.

No alpha channel anywhere, on either store.

And never re export from an export. Go back to the original every time.

One format, one bit depth, no transparency. That is the entire decision, and it takes a minute to set up once.