You drag three screenshots into an email, hit send, and the message bounces — or it sits in the outbox forever, or the recipient's mail server quietly rejects it. The culprit is almost always PNG. A full-screen screenshot of a dashboard can easily be 6–12 MB as a PNG, and three of those blow past most attachment limits before you've typed a word.
Converting PNG to JPG usually cuts that by 80–95% with no visible difference on screen. That same 9 MB screenshot lands around 400–700 KB as a JPG at a sensible quality setting. This article covers the conversion itself: which quality number to pick, the one case where JPG visibly hurts (red text), and what happens to transparent areas.
Why PNG files are so big in the first place
PNG is lossless. Every pixel is stored exactly, which is wonderful for logos and diagrams and terrible for photos or screenshots full of gradients, shadows and antialiased text. There's no quality dial to turn down — PNG either stores the image perfectly or not at all.
JPG throws away detail your eye doesn't notice: fine variations in colour, tiny differences between neighbouring pixels. That's why screenshot-2024-dashboard.png at 9.2 MB becomes screenshot-2024-dashboard.jpg at 520 KB. Same picture, 94% smaller, and in an email client at normal zoom you genuinely cannot tell.
Most mail providers cap attachments somewhere in the 20–25 MB range, and many corporate gateways set it far lower — 10 MB is common. The gmail attachment size limit image problem isn't that one image is huge; it's that four of them together are. Convert first, attach second.
The quality setting in practice: q85 vs q95
JPG quality runs 1–100. It is not a percentage of anything meaningful — it's a dial on how aggressively detail gets discarded. Three numbers are worth knowing:
- q95 — near-indistinguishable from the original, even if you zoom in. Files are roughly twice the size of q85. Use it for photos someone will print or crop.
- q85 — the practical default. Artefacts exist but you need to zoom to 200% and know where to look. This is the setting for email, chat, tickets and uploads.
- q70 and below — visible blockiness around edges and text. Fine for a thumbnail, wrong for anything a colleague will read.
Real numbers from a 1920×1080 screenshot that started as a 9.2 MB PNG: q95 gives about 1.1 MB, q85 about 520 KB, q70 about 310 KB. Going from q85 to q95 doubles the file for a difference nobody will see in Outlook. Going from q85 to q70 saves 200 KB and makes your text look crunchy. Stay at 85 unless you have a specific reason not to.
Chroma subsampling: why red text goes fuzzy
Here's the part that surprises people. Most JPG encoders use 4:2:0 chroma subsampling by default: brightness is stored at full resolution, but colour information is stored at half resolution horizontally and vertically. Your eye is far more sensitive to brightness than colour, so this is nearly free compression — for photographs.
It falls apart on saturated coloured text on a contrasting background. Red error text on white, or white text on a red button, has almost no brightness variation to carry the shape — the edge lives entirely in the colour channel that just got halved. The result is smeared, slightly orange-fringed lettering that looks blurry even at q95.
If your screenshot contains red warnings, coloured badges or thin coloured UI text, switch to 4:4:4 (no subsampling). It costs maybe 10–15% more file size and the text comes back sharp. If the image is a photo of people, a product or a document scan, leave it at 4:2:0.
What happens to transparency
JPG has no alpha channel. None. Any transparent pixel in your PNG has to become a solid colour during conversion, and the encoder picks one for you — historically black, which is how people end up with a logo sitting on an ugly dark rectangle.
For screenshots and photos this never comes up, because they're fully opaque already. It matters for logos, icons and anything exported with a cut-out background. The fix is to flatten deliberately onto white (or whatever colour the destination page uses) rather than letting the encoder guess. If transparency is essential to the image, JPG is the wrong target format — keep the PNG, or compress the PNG itself.
The fast route: convert PNG to JPG in the browser
For one email's worth of images, don't install anything. Open the PNG to JPG converter, drop the files in, pick a quality level and download the results. Nothing is installed and you can do it from a locked-down work laptop.
A realistic workflow for an email:
- Drop
invoice-screenshot.png(7.4 MB) anderror-dialog.png(2.9 MB) into the converter. - Choose quality 85, or the high-quality option if the image has coloured text.
- Download
invoice-screenshot.jpg(410 KB) anderror-dialog.jpg(180 KB). - Attach the JPGs — under 600 KB total instead of 10.3 MB.
If you also need PDFs, WebP or HEIC handled, the image converter hub covers the other direction and the other formats.
The command line route with ImageMagick
If you're converting a folder of files regularly, ImageMagick's magick command is faster than any UI. One file:
magick screenshot.png -quality 85 screenshot.jpgScreenshot with red text — force full colour resolution:
magick screenshot.png -quality 90 -sampling-factor 1x1 screenshot.jpgA logo with a transparent background, flattened onto white instead of black:
magick logo.png -background white -flatten -quality 90 logo.jpgA whole folder at once:
magick mogrify -format jpg -quality 85 -path ./jpgs *.pngThe -path ./jpgs part writes into a separate folder so your originals survive. Always keep the PNGs until you've checked the output — JPG compression is one-way, and re-saving a JPG repeatedly degrades it a little each time.
A sane default you can reuse
Memorise one recipe and you'll almost never think about this again: quality 85, 4:2:0 for photos; quality 90, 4:4:4 for screenshots with coloured text; flatten onto white if there's transparency. That covers nearly everything an office worker attaches to an email.
Before you send, glance at the JPG at 100% zoom — especially around text and sharp edges. If it looks clean there, it will look clean to the recipient. And if the attachment is still too big after conversion, the remaining problem is pixel dimensions, not format: a 6000-pixel-wide photo is overkill for an email no matter how it's encoded.
FAQ
Does converting PNG to JPG lose quality? Yes, but at quality 85 the loss is invisible at normal viewing size. The original PNG is untouched — you're creating a new file, not modifying the old one.
How much smaller will the JPG be? For screenshots and photos, typically 80–95% smaller. A 9 MB PNG commonly lands between 300 KB and 1 MB. Simple graphics with large flat colour areas shrink less, because PNG already handles those well.
Can I convert back to PNG later? You can change the format back, but the discarded detail doesn't return. Keep your original PNG if you might need to edit the image again.
Why does my converted logo have a black background? JPG can't store transparency, so the transparent pixels became black. Re-convert with a white background flatten, or keep the logo as PNG.
What if JPG still isn't small enough? Reduce the pixel dimensions. Resizing a 4000×3000 photo down to 1600×1200 cuts the file roughly another 80%, and it's still larger than most screens display in an email.
Is JPG or JPEG correct? They're the same format. .jpg is the three-letter version from older Windows; .jpeg is identical in content and both open everywhere.