Why screenshots compress badly
JPEG was designed for photographs. It works by throwing away detail your eye is bad at noticing, and your eye is bad at noticing fine variation inside a leafy tree. It is excellent at noticing a grey smudge next to a black letter on a white background.
That smudge has a name, mosquito noise, and it is what you see when a screenshot has been through a lossy encoder at a low setting. Text develops a halo, thin lines get soft, and flat colour blocks pick up faint blotches.
Two things follow. Keep the quality setting up. And if the screenshot is already a PNG, which it is on every phone and most desktops, do not run it through several converters in a row, because each one costs you another pass.
What each platform gives you
| Device | Screenshot format | Faster built-in route to PDF |
|---|---|---|
| iPhone, iPad | PNG | Share sheet, Print, then pinch out on the preview and Save to Files |
| Android | PNG | Share, Print, then Save as PDF |
| macOS | PNG | Open in Preview, File, Export as PDF |
| Windows | PNG | Open in Photos, Print, Microsoft Print to PDF |
Every one of those is faster than a website for a single screenshot. This page earns its place when you have eight of them, want them in one document, and want the order right.
Full page screenshots
On iPhone, a Safari screenshot has a Full Page tab in the markup screen that captures the whole scrollable page rather than the visible part. Tap it, then Done, then Save PDF to Files. That is already a PDF and it holds real text, not a picture of text, which is strictly better than anything you can do here.
On desktop Chrome and Firefox, the developer tools have a full page capture command, and Firefox has one in the right click menu under Take Screenshot. Those produce PNGs, which you can bring here.
Before you convert a screenshot of something private
Screenshots are the most sensitive images most people convert: bank apps, message threads, boarding passes, medical portals. Two habits worth having.
Crop or black out anything you do not need before converting. Once it is a PDF page it is a picture, and picture editing is more annoying than cropping a screenshot in Photos. Second, be deliberate about which converter you use. This one runs entirely in your browser and the files are never sent anywhere, which you can verify by turning off your network connection after the page loads and converting anyway.