Screenshots are everywhere: payment proofs, chat backups, bug reports, tutorials. But a single full-screen screenshot on a laptop can easily be 400 KB to 1.7 MB, and they pile up fast. So what is the best image format for screenshots? We tested 8 formats on 22 real screenshots, checked every result pixel by pixel, and the results surprised us. Then we built a new format just for screenshots, and it beat them all.
Why Are Screenshots So Big?
Screenshots are saved as PNG on most devices. Windows does this, Macs do this, iPhones do this, and most Android phones do too (a few brands use JPG). PNG is lossless: it keeps every pixel exactly, so text stays perfectly sharp. That’s the right choice for screenshots, but it comes at a cost.
Modern screens have a lot of pixels. A laptop screen of 2256 × 1504 is over 3.3 million pixels, and every one of them is stored. On top of that, the PNG files your computer saves aren’t squeezed very hard, because the device saves them quickly instead of making them as small as possible.
In our test, the PNGs Windows saved were 48% bigger than the same PNGs after full optimisation. Same image, same quality, just packed better.
Why Not Just Save Screenshots as JPG?
JPG makes files small by throwing away detail. That works for photos, where nobody notices. But screenshots are mostly text, sharp edges and flat colours, and JPG handles those badly: letters get blurry, and you see smudgy “noise” around text and icons.
For screenshots you want a lossless format, one that keeps every pixel exactly the same. The real question is which lossless format makes the smallest file.
We Tested 8 Formats on 22 Real Screenshots
We took 22 full-screen Windows screenshots (2256 × 1504) of everyday screens: Gmail, Shopify admin, Razorpay, Google Sheets, Google Drive, Figma and several websites, in both light and dark mode. Then we saved every screenshot in every format below, all lossless, and checked that each file decoded back to the exact original pixels.
Here are the total sizes for all 22 screenshots:
| Format (lossless) | Total size | Compared with optimised PNG | Avg. time to save | Avg. time to open |
|---|---|---|---|---|
| SSIMF (new) | 6.24 MB | 34% smaller | 0.61 s | 0.09 s |
| WebP lossless (max effort) | 7.06 MB | 25% smaller | 7.52 s | 0.01 s |
| WebP lossless (default) | 8.51 MB | 10% smaller | 1.24 s | 0.02 s |
| PNG (fully optimised) | 9.44 MB | same | 5.88 s | 0.01 s |
| JPEG XL lossless | 9.49 MB | 1% bigger | 1.91 s | 0.41 s |
| PNG (as Windows saves it) | 13.93 MB | 48% bigger | – | 0.01 s |
| AVIF lossless | 15.38 MB | 63% bigger | 4.63 s | 0.11 s |
| QOI | 17.62 MB | 87% bigger | 0.01 s | 0.01 s |
Times were measured on a small 2-core cloud computer, so your computer will likely be faster. All formats used the same screenshots.
What the Results Mean
PNG: safe everywhere, but bigger than it needs to be
PNG opens on every phone, computer, app and website, which is why it’s the default. But the PNGs your device saves are far from the smallest they could be. Running them through an optimiser cut a third of the size without changing a single pixel.
WebP lossless: the best everyday choice today
Lossless WebP made files 25% smaller than optimised PNG at its strongest setting, and every modern browser can show it. If you put screenshots on a website or blog, lossless WebP is the best practical choice today. You can convert PNG screenshots to WebP free with our Image Converter.
AVIF lossless: great for photos, not for screenshots
This was the biggest surprise. AVIF is famous for tiny photo files, but in lossless mode it made screenshots 63% bigger than optimised PNG. It was built for photos and video, not sharp text.
JPEG XL lossless: roughly a tie with PNG here
At its standard setting, JPEG XL came out about the same size as optimised PNG on these screenshots, and it was the slowest to open. It can do better at its slowest settings, but those take much longer to save.
QOI: lightning fast, but big files
QOI saves and opens almost instantly, which is why some games and tools use it. But its files were nearly twice the size of optimised PNG. It’s built for speed, not small files.
Meet SSIMF: A New Image Format Made for Screenshots
None of these formats were designed with screenshots in mind. So we built one. SSIMF stands for ScreenShot IMage Format. It’s lossless like PNG, and on our 22 screenshots it was:
- 34% smaller than fully optimised PNG
- 12% smaller than lossless WebP at WebP’s strongest setting
- 55% smaller than the PNGs Windows saved, so less than half the size
- About 12 times faster to save than WebP at that setting
It came out smaller than WebP on every single one of the 22 screenshots, and every file opened back to the exact original pixels.
One honest note: we tuned SSIMF’s settings using these same screenshots, so on other screenshots the lead may be smaller. That’s why it’s free to test yourself, and why we’d love to hear your results.
How Does SSIMF Make Screenshots So Small?
Screenshots repeat themselves a lot: the same letters, icons, buttons and table rows appear again and again. For every pixel, SSIMF asks four questions in order:
- Is this a copy of something earlier? Repeated words, icons and rows are stored as “copy those pixels from over there” instead of being saved again.
- Is it the same as a neighbour? Big flat areas, like white backgrounds, cost almost nothing.
- Is it a colour used recently? The soft edges of text reuse a handful of blended colours, so SSIMF keeps them close at hand.
- If not, spell it out. New colours are predicted from the pixels around them, so only a small difference needs to be stored.
Each answer is written with a smart coder that learns as it goes, so common answers take only a tiny fraction of a bit.
How to Try SSIMF for Free
- Open the SSIMF converter.
- On the Convert tab, drop in one or more PNG screenshots.
- See how much smaller each one gets, then download your .ssimf files (one by one or as a ZIP).
- To open an SSIMF file later, use the View tab on the same page. You can save it back as PNG or JPG anytime.
Everything runs in your browser. Your screenshots are never uploaded anywhere.
On Windows, you can also install the free SSIMF Viewer from the SSIMF page. After that, .ssimf files open with a double-click, just like PNG.
When You Should Not Use SSIMF (Yet)
SSIMF is brand new, and we’d rather be honest about its limits:
- Don’t send .ssimf files to other people unless they know about it. WhatsApp, phones, browsers and most apps can’t open SSIMF yet. For sharing, use PNG, or compress the screenshot to a smaller JPG or WebP.
- Don’t use it for photos. Like PNG, it’s lossless, so camera photos come out bigger, not smaller. Photos are better as JPG, WebP or AVIF.
- Keep your originals for now. SSIMF is experimental (version 1), so don’t make it the only copy of something important.
Where SSIMF already shines is storing lots of screenshots: archives, documentation, bug reports, or that folder of 2,000 screenshots eating up your drive.
Best Image Format for Screenshots: Quick Answer
| What you’re doing | Best format |
|---|---|
| Sharing on WhatsApp, email or social media | PNG (opens everywhere) |
| Putting screenshots on a website or blog | Lossless WebP |
| Uploading to a form with a size limit | JPG or WebP, compressed to the size you need |
| Storing lots of screenshots to save space | SSIMF (new, experimental) |
| Photos (not screenshots) | JPG, WebP or AVIF, not lossless |
For Developers: SSIMF Is Free and Open Source
The SSIMF encoder and decoder are about 300 lines of C or JavaScript, with no dependencies, under the MIT licence. The JavaScript version makes byte-for-byte the same files as the C version. You’ll find the code, the file layout and build steps on GitHub. If you test SSIMF on your own screenshots, we’d love to see the numbers.
Frequently Asked Questions
What is the best image format for screenshots?
A lossless format, so text stays sharp. For sharing, PNG is the safest because it opens everywhere. For websites, lossless WebP is about 25% smaller than optimised PNG. For storing lots of screenshots, the new SSIMF format was 34% smaller than optimised PNG in our tests.
Why are my screenshots saved as PNG?
Most devices save screenshots as PNG because it’s lossless, which keeps text and edges perfectly sharp. The downside is larger files, especially on high-resolution screens.
Is WebP better than PNG for screenshots?
Lossless WebP keeps the exact same quality as PNG and made files 10–25% smaller in our tests, depending on the setting. Every modern browser supports it, so it’s a great choice for websites.
Why shouldn’t I save screenshots as JPG?
JPG throws away detail to save space. On screenshots that shows up as blurry text and smudges around letters and icons. It’s fine for photos, not for text.
How do I reduce screenshot file size without losing quality?
Use a lossless format that packs pixels better: optimise the PNG, convert to lossless WebP, or try SSIMF. All three keep every pixel exactly the same.
What is SSIMF?
SSIMF (ScreenShot IMage Format) is a new lossless image format made by imgformats specifically for screenshots. On 22 real screenshots it was 34% smaller than optimised PNG and 12% smaller than lossless WebP.
How do I open an SSIMF file?
Use the View tab on the imgformats SSIMF page, which works in any browser. On Windows, you can install the free SSIMF Viewer to open .ssimf files with a double-click.
Is SSIMF lossless?
Yes. Every pixel is kept exactly. In our tests, every SSIMF file was checked against the original screenshot and matched pixel for pixel.