Joined, and now it’s enormous
Six screenshots do not make a picture six times taller than a phone screen — they make one that is often taller than anything will comfortably open. Here is the arithmetic, and what to do about it.
How it gets so tall so fast
A recent iPhone screenshot is 1,170 × 2,532. Six of them stacked whole would be 15,192 pixels tall. Cutting the repeated bands out brings that down — a typical scroll leaves perhaps a third of each capture repeating the one before it, so six captures might come out around 10,000 — but it is still four times taller than anything you have looked at today, and about 12 megapixels of mostly text.
Stacking a column of photographs does the same thing more quietly. Twenty holiday photographs at 3,024 pixels tall, matched on width and stacked, is 60,000 pixels of picture. It will not draw, and the tool says so rather than handing back the top of it.
Where the browser stops
Every browser has a limit on how large a single canvas can be, and the limits are lower than people expect. Chrome and its relatives refuse a dimension past 32,767 pixels and an area past roughly 268 megapixels. Safari on a phone gives up much earlier — and, worse, it often gives up silently, handing back a blank canvas instead of an error. That is why this tool checks the finished size against the ceiling before it draws anything, and stops with the numbers rather than producing a tall white rectangle.
The export is composited in bands of a few thousand rows at a time so a very long join does not lock the tab while it is being drawn. That makes the work bearable; it does not raise the ceiling, because the finished picture still has to exist in one piece for the browser to turn it into a file.
What to do instead
- Join in halves. Three captures, save. Three more, save. Then join the two results. Each step stays well under the ceiling and the seams are unchanged.
- Bring the size down first. Switching the sizing policy to “match the smallest” pulls the whole result down proportionally. On a set of screenshots that are all the same width anyway, this changes nothing about the arrangement.
- Ask whether it needs to be one picture at all. A 10,000-pixel receipt is unreadable in every message app and most photo viewers — they scale it to fit and it becomes a thin illegible strip. Three separate pictures are often more useful than one tall one.
Putting it back
Sometimes you finish a join, look at it, and realise the useful artefact was the pieces. Cutting one long picture back into several files is the exact reverse of what happens here, and this site does not do it yet. Any splitter that cuts into equal parts or a grid will give you a set again — with the repeated bands already gone, which is the one thing the original captures could not give you. Until then, the quickest route is to join fewer captures at a time: three or four per file reads well in a message app.
What a very tall picture costs
Two things, both worth knowing before you commit. Memory: a picture that is 1,170 × 10,000 is 11.7 million pixels, and while it is being assembled it occupies about 47 MB of uncompressed pixels regardless of how small the saved file ends up. On a phone with several tabs open that is enough to have the tab reloaded underneath you. And weight: PNG keeps text crisp and a tall screenshot in PNG is frequently 5 to 15 MB, which is past what several messaging apps will send without re-encoding it themselves.
The joiner reports the finished dimensions and a rough file size honestly and stops there — on a tall screenshot it does not hunt for a number of kilobytes, because squeezing text that hard ruins it. Switching to JPEG, or to the “match the smallest” sizing policy, brings the weight down without guesswork. The one page here that does search for a kilobyte range is the photo-and-signature page, where forms state one.