Why Your Screenshot File Is So Large

You capture a long page, go to attach it to an email, and the mail client refuses. Twenty-two megabytes for a picture of a web page seems absurd, and it is worth understanding before you go looking for a compressor.

Why the number is so large

Three things multiply together, and each of them is bigger than people expect.

• The image is enormous in pixels. A page that takes twelve screens to read is roughly twelve times the height of your display. At a typical laptop size that is an image around 1,400 by 12,000 — about seventeen million pixels, where a photograph from a phone is around twelve.
• A sharp screen doubles or triples that. Capturing at your screen’s real resolution is what keeps the text crisp, and it also means two or three times as many pixels in each direction. That is four to nine times the total.
• PNG does not throw anything away. It is a lossless format, which is the right choice for text and interface elements — it keeps edges clean where JPEG would smear them. It also means the file cannot get small the way a photograph can.

A twenty megabyte file is not a bug. It is what those three facts produce when multiplied.

What to do, in the order worth trying

1. Send a PDF instead. For a page that is mostly text and interface, this is usually the biggest single saving, and the result stays sharp when the recipient zooms in. It is also what most people actually want when they are sending a web page to someone — a document, not a picture of one.
2. Send less page. The honest question is whether the recipient needs all twelve screens. A capture of the section that matters is smaller, faster to send, and easier to read than the whole thing.
3. Capture at a lower zoom. Ctrl or Cmd and minus before capturing puts more page in fewer pixels. At 67% the file falls by more than half. The text gets smaller rather than blurrier, which is a better trade than it sounds.
4. Convert to JPEG, carefully. A JPEG of the same image is often a tenth the size, and on a page of photographs the loss is invisible. On a page of small text it is not — JPEG puts a faint halo around hard edges, and screenshots are made of hard edges. Look at the result at full size before sending it.
5. Put it somewhere and send a link. Beyond a certain size this is what everyone ends up doing, and it sidesteps every attachment limit at once.

The limits you are running into

Gmail and most mail providers cap attachments at 25MB, and the encoding used to send them adds about a third, so a file over roughly 18MB will be refused even though the stated limit is higher. Slack and most chat tools sit around 1GB and are not the problem. Ticketing systems are frequently much lower than either — 5MB and 10MB caps are common, and they are where this question usually comes from.

Why compressing afterwards disappoints

Running a PNG through an optimizer typically saves ten to twenty per cent. That is real, and it is rarely the difference between refused and accepted, because the problem is the pixel count rather than the encoding. Every option above attacks the pixel count instead, which is why they work better.

If the image also came out soft, that is a separate problem with its own causes — why your full-page screenshot came out blurry covers them.

What PageStill does

It saves as a PNG, and in the editor it can save as a PDF instead. For a long page headed for an email or a ticket, the PDF is normally both the smaller file and the better thing to receive.