Split a Long Image Into a Multi-Page PDF

Why one tall image on one page turns into a grey strip

Take a scrolling capture 1,000 pixels wide and 20,000 tall. Asked to fit it on one A4 page, any converter has to shrink the whole thing until the height fits. At normal screen resolution 20,000 pixels is about 208 inches; an A4 page is 11.69 inches tall. That is a scale of roughly 5.6 per cent, and about 5 per cent once you add margins.

The width shrinks by exactly the same amount, so the finished page is a strip about 15 mm wide running down the middle of an otherwise empty sheet. Text that was 16 pixels tall on your screen ends up under a single pixel. The pixels are still in the file — the converter embeds the image whole and simply draws it small — so a viewer will resolve more detail as you zoom. But you are then panning a 15 mm ribbon at enormous magnification, and on paper it is gone for good.

Switching the fit to fill-and-crop does not rescue anything either. It scales the image to cover the page, which means matching the width and letting the height overflow. The overflow is trimmed evenly top and bottom, so you keep a band from the middle of the capture and lose everything else.

First, check whether you need the image at all

This is the step most guides skip, and it produces a better PDF than anything below. A tall image is almost always a photograph of something that still exists in a better format.

• A web page you screenshotted. Go back to the page and press Ctrl+P, or Cmd+P on a Mac, then choose Save as PDF. The browser paginates it properly, the text stays real text you can search and copy, and nothing gets scaled to 5 per cent.
• A chat log. WhatsApp has Export chat, which gives you a .txt of that one conversation, and Telegram Desktop has Export chat history, which can write readable HTML. Both print far better than a stitched screenshot ever will. Signal's Export chat history writes your whole history as JSON, which is a data file rather than something you can print.
• A long receipt or order confirmation. Most retailers and banks keep a download-PDF or print-receipt link in the account area, and their version is already page-shaped.

Slice the image only when the source is genuinely gone: an app with no export, a webtoon strip, a design mock-up, a screenshot somebody sent you. Then the rest of this page applies.

Option one: one very tall page, and the 200-inch wall

If the PDF only ever has to be read on a screen, you do not have to split it at all. Set page size to Match the image and margin to none, and the converter builds a single page exactly the shape of your capture. It scrolls like the original and nothing is scaled down.

The catch is a ceiling inherited from Acrobat: at the default unit a page tops out at 14,400 points, or 200 inches, and most other viewers follow the same limit. You do not have to police this yourself. If a match-the-image page would overshoot, the converter raises the assumed resolution until it fits and tells you it did, without touching a pixel — the page just becomes physically smaller. The table below shows what each setting asks for before that correction, which is worth knowing if you plan to print.

Raising the dpi throws nothing away. It packs more pixels into each inch, so the page gets physically smaller while the detail stays identical, which on screen makes no visible difference. On paper it makes every difference. No printer takes a 133-inch sheet, so the print dialog will shrink the page down to fit your paper and you are back to the unreadable strip. There is more on what the dpi setting actually controls in our guide to converting images to PDF at 300 dpi. If the file has to come out of a printer, split it instead.

Option two: split the image into multiple PDF pages

The converter on this page can do the cutting for you. Set Long images to "Split long images across pages" and it slices the capture into page-shaped bands, with a little overlap, in the order they run down the image. Pick a fixed page size such as A4 or US Letter, drop the tall image in, and convert.

Cutting the bands yourself in an image editor is only worth it when you want to choose exactly where each break falls, or when you want a wider overlap than the default. That route is three steps.

1. Work out the band height for your page size, using the table in the next section.
2. Cut the tall image into bands and save them as separate files named so they sort correctly: slice-001.png, slice-002.png and so on. Zero-pad the numbers, or slice-10 will sort ahead of slice-2.
3. Drop all the bands into the converter above, check the thumbnail order, and convert to one merged PDF.

Free ways to do the cutting: GIMP, where you drag horizontal guides to the cut points and then use Image, Slice Using Guides. Each piece opens as a separate image inside GIMP and you export them one at a time. It gives you no overlap. Paint or Photos on Windows and Preview on a Mac, fine if you only need three or four pieces and do not mind cropping and saving by hand. Or ImageMagick, which is the only one of the three that will do overlap for you in a single line:

for y in $(seq 0 1320 19999); do magick long.png -crop 1000x1470+0+$y +repage "$(printf 'slice-%05d.png' $y)"; done

That takes 1,470-pixel bands every 1,320 pixels, leaving 150 pixels of overlap, and names them so they sort themselves. Slicing has a second benefit: a very large single image is refused with an explanation, and each band is comfortably under any such ceiling.

How tall each band should be

A band should be the same shape as the printable area of the page, so it fills the sheet instead of sitting in a letterbox. Divide the usable page height by the usable width, then multiply by your image's pixel width.

Scale it for other widths the same way: a 1,440-pixel-wide phone capture on A4 with a 13 mm margin wants bands of about 2,121 pixels. Round to something tidy, because being twenty pixels out is invisible. With 1,473-pixel bands and 150 pixels of overlap, a 20,000-pixel capture comes out as sixteen pages. Set fit to fit inside the page rather than fill-and-crop, so the edges of each band survive.

Overlap, so a line of text is never cut in half

Cut at an arbitrary pixel row and sooner or later the cut lands through the middle of a line of text: the tops of the letters on one page, the bottoms on the next. That is unreadable, and it looks like a mistake rather than a page break.

Overlap fixes it. Start each band slightly above where the previous one ended, so the last line or two of one page reappears at the top of the next and the reader can join them without thinking about it. Between 100 and 200 pixels is right for a typical screenshot, roughly two lines of body text. Below 100 a large heading can still be bisected; above 300 you are repeating enough content to add pages you did not need.

If you are cutting by hand and there are only a few pages, do better than a fixed interval. Put each cut in a natural gap: between two chat bubbles, just above a heading, after the last row of a table. A cut nobody notices beats a cut the reader has to reconcile.

Settings for the bands, and what you end up with

Once the bands exist, the conversion is quick. Page size A4 or US Letter, orientation portrait, margin matching whatever you assumed in the band maths, fit set to fit inside the page, output as one merged PDF with a sensible file name.

Save the bands as PNG if the capture is mostly text, since a JPEG re-save softens small letterforms. Either way the conversion step costs you nothing in quality: a JPEG's own bytes go into the PDF untouched, and a PNG is re-packed losslessly, pixel for pixel. Whatever loss there is happened in the editor you cut the image in. For an ordinary single-screen capture that needs no slicing at all, the converter at the top of this page is the shorter route.

Before you convert, look at the thumbnails. They appear in the order they will be written, you can drag them or nudge them with the arrow buttons, and you can delete a duplicate band without starting again. Then one honest caveat: the result is a stack of pictures. There is no OCR here, so the text in your capture stays a picture of text, neither searchable nor selectable. If a sixteen-page file comes out heavier than you expected, why PDFs get big after converting images covers what to change.