How I designed a long screenshot app for iPhone

iPhone still has no system-wide long screenshot. Taking a screenshot and choosing Full Page only works in Safari and a few of Apple's own apps, and what you get is a PDF. Chats, orders and long articles inside other apps all need a third-party app. Rollshot is the app I built for this: record the screen while you scroll and the long screenshot builds itself. The things you most often do next, blurring things out, adding a watermark, stitching subtitle lines, happen in the same place.

This isn't a comparison of which app is best. It's why I made this one, and what I was thinking about while I made it.

Where it started: the long screenshot is only half the job

Once I wanted to save a chat as one long image and send it to a friend. My first approach was to take screenshots one by one, move them to my Mac and stitch them together in an image editor. It was painful: I had no idea how tall to make the canvas, and once it was stitched I still had to blur out some of the content.

Later I looked for a ready-made long screenshot app on the App Store. The ones I tried had much the same problems: the free version put a watermark on the exported image and removing it cost money, or ads kept popping up, or the price was a weekly or monthly subscription, for a small tool that just makes long screenshots. The features weren't necessarily bad; it was the way they charged that made them uncomfortable to use. That's what made me decide to build my own: making a long screenshot is free, there are no ads, and if anything costs money it's a single purchase.

Looking back, a finished long screenshot isn't the end. It's an intermediate step before you send it, and before you send it there are usually a few more things to do:

• Hide what shouldn't be seen: avatars, phone numbers, order numbers, addresses.
• Mark where it came from: it's your own content, and you don't want it reposted as someone else's.
• Keep only the part that matters: from a few screenshots of a film, all you really want to share is a few lines of subtitles.

If those steps mean passing the image between three apps, every hand-off is another save to Photos, another search through your library, and another round of compression. So from the start I decided that the most common steps after a long screenshot would happen in the same app.

Three ways in, for three kinds of "long"

Long content doesn't come from one place, so there are three ways in:

• Scroll & record: tap Start, go to the page and scroll down. Pause for three seconds and the long screenshot is ready. Anything that scrolls works, because the recording is done by iOS itself.
• Stitch screenshots: if you already have a few screenshots, just pick them, in any order. They're lined up by content. Adjacent shots only need to overlap by a line or two of text.
• Web page: paste a link and the whole page is rendered as one image.

What I held on to in the design

Where it doesn't fit, mark it; don't guess

The worst thing a long screenshot can do isn't failing to stitch. It's stitching wrong without telling you: a piece is missing in the middle and you send it without noticing. So a seam that might be missing content is marked in orange, and when you stitch screenshots, the one that doesn't fit is clearly marked rather than forced into some position.

The stitching algorithm went through several versions to make it as accurate as I could. But pages that scroll vary endlessly, and it can't be right 100% of the time. So anything that's marked has to be fixable: on the result page, drag the part below a seam until the content lines up, or delete the segment that went wrong.

One less step is one less thing to forget

• Stop scrolling for three seconds and it finishes on its own; you don't have to come back and tap Done.
• Only the few frames needed for stitching are kept, so there's no screen recording left in Photos for you to delete.
• A header pinned to the top of the page is kept once, and the status bar and scrollbar are removed, so they aren't repeated at every seam.

Blurring out should really remove it

Blur out as pixels or as blur, and in a chat screenshot you can hide every avatar at once. At export that area is redrawn, so the original content isn't in the file. It isn't a coloured box laid on top.

The watermark goes only on the copy you send

The watermark is tiled, in a grid or staggered, and you choose the text, density, angle, opacity and colour. It's added only to the exported copy; the original in your library is untouched. To try a different watermark, or send it again without one, you don't need to capture it again.

Subtitle stitching: keep only the line you want

You took a few screenshots while watching a show, and what you want to share is just the subtitle line. Subtitle stitching keeps that strip from each image and stacks them into one. You can also give it a video clip and every line becomes a strip. This is the one place that keeps the order you picked, because only you know which line came first.

Tell you how big it is before you export

Export has three sizes, original, WeChat-friendly and custom width, and shows the file size before you save. Long screenshots easily run to tens of megabytes, so it helps to know the size before choosing which one to send.

Your images don't leave your phone

No account, no ads, no analytics. Screenshots are picked with the system photo picker, so no photo library permission is needed. Apart from the web page feature, which has your phone load the URL you enter directly, everything works offline and your images are never uploaded.

About pricing

Making a long screenshot shouldn't cost anything: all three ways in are free all the way to a full-resolution export, at any length. There's just a small signature line under the image, which you can crop off, and the library keeps your latest 20. Blur out, watermark and subtitle stitching can be previewed for free.

For people who need those, Pro is a single purchase ($4.99) with Family Sharing. No subscription, and no second tier.

If you only need one now and then

If you only capture web pages in Safari, the built-in option is enough: take a screenshot, tap the preview in the bottom-left corner, choose Full Page and save it as a PDF. If you need to capture chats or content inside other apps, or blur things out and add a watermark before sending, that's when an app is worth installing.