A seamless carousel, one wide picture split across several slides that join when you swipe, is one of the few formats that makes a panorama work on a phone. It is also easy to get wrong: a slide that is a few pixels off shows a jump at the seam, a picture of the wrong shape gets squashed, and a seam that runs through someone's face splits them in two. This article works through the numbers with one example and the image splitter, whose cut positions were used for every figure below.
The shape a carousel needs
Instagram shows every slide of a carousel at the same shape, and the common choices are square (1:1), portrait (4:5, 1080 × 1350 px) and landscape (1.91:1, 1080 × 566 px). A carousel of n slides placed side by side therefore has the shape n × the slide ratio:
| Slides | Square 1:1 | Portrait 4:5 |
|---|---|---|
| 2 | 2 : 1 | 1.6 : 1 |
| 3 | 3 : 1 | 2.4 : 1 |
| 4 | 4 : 1 | 3.2 : 1 |
| 5 | 5 : 1 | 4 : 1 |
Your panorama has its own shape. If it matches one of these, it splits with nothing lost. If not, something must be cropped, because the only alternative is stretching, which makes people look wider or thinner and is never worth it.
A worked example
Take a panorama of 6000 × 2000 px, a 3 : 1 picture.
As three squares, it fits exactly: 3 × 1 = 3 : 1. The slides are 2000 × 2000 px each, cut at x = 2000 and x = 4000, and each is scaled to 1080 × 1080 for posting. Nothing is lost.
As 4:5 portrait slides, the tool's "fit to the picture" suggests 3 / 0.8 = 3.75, rounded to 4 slides, which need 3.2 : 1. The picture is a little too narrow for that, so the full width is kept and the height is cut to 6000 / 3.2 = 1875 px: 125 px, or 6.25% of the picture, is trimmed from the top and bottom together. Each slide is 1500 × 1875 px, the seams fall at x = 1500, 3000 and 4500, and every slide is saved at 1080 × 1350.
As three 4:5 slides instead, the carousel needs 2.4 : 1, so the full height is kept and the width is cut to 2000 × 2.4 = 4800 px: 1200 px, a fifth of the picture, disappears from the sides. The crop position control decides which fifth.
Choosing between these is a design decision, but the tool shows the cost of each in the preview and says how much is left out.
Exact seams
A carousel only looks seamless if the right edge of each slide is exactly the left edge of the next. Two common mistakes break this:
- Overlapping or skipped pixels. If a 1000-pixel strip is split into three by making every piece 333 px, one pixel column is lost; making them 334 duplicates one. The splitter places each cut at the whole pixel nearest the exact position, so 1000 becomes 333, 334 and 333, and every pixel is used once.
- Resizing each slide separately from a different crop. Scale after cutting, all slides by the same factor, which is what the "scale to 1080 px" option does: in the 4:5 example every slide goes from 1500 to 1080 px wide, a factor of 0.72.
Keeping faces out of the cuts
The seams are fixed by the maths, so the only freedom is where the picture sits relative to them. Some practical rules:
- Look at the seam lines before saving. The preview draws each one and numbers the slides. If a seam crosses a face, move the crop position or change the number of slides: in the example, the seams at 1500, 3000 and 4500 px (four slides) and 2000 and 4000 px (three squares) fall in different places.
- Give people a margin. On a phone, the swipe animation and rounded corners make the outer few dozen pixels of each slide hard to look at. A face or a word that sits close to a seam is uncomfortable even when it is not cut.
- Put the subject in a slide, not across two. The first slide does most of the work in the feed, so the most important part of the picture belongs there, whole.
- Text never crosses a seam. If the panorama has a sign or a caption on it, choose the split so the text stays inside one slide.
The 3 × 3 profile grid
The same maths applies to a grid split for a profile page. A 3000 × 3000 picture splits into nine pieces of 1000 × 1000. Two things to remember: the newest post appears first, so post the pieces in reverse (bottom right first, top left last), and the grid has small gaps between tiles, so a line or a face crossing a cut looks broken there too.
Common mistakes
- Stretching the panorama to fit. Crop instead, and choose what to lose.
- Mixed shapes in one carousel. The slides are shown at one shape; mixing them makes some appear with borders or cropped.
- Uploading full-size slides. A 2000-pixel slide is resized by the app; saving at 1080 px avoids a second, uncontrolled resize.
- Ignoring the order. Name the files so they sort in posting order; the splitter writes
photo-01,photo-02and so on.
Recipe
- Straighten or crop the panorama first if needed, with the image crop tool.
- In the image splitter, choose Carousel slides and the slide shape.
- Start from "fit to the picture", then try one slide more and one fewer; watch where the seams fall.
- Slide the crop to keep faces and text away from seams.
- Keep "scale each slide to 1080 px" on and download the ZIP.