In our most recent update to the Instagram iOS app we added a simple way to make it easier to take beautiful photos. When you take a photo with the in-app camera, you can now tap the new straighten icon and your photo will correct to be level—it’s that simple. The straightening tool also includes a slider so you can rotate and adjust any photo—including ones imported from your photo library—as much or as little as you’d like.

We had been talking about adding a way to auto straighten photos for a while, even before we started working on video. As a team we had been thinking about the problem, as it is easy to accidentally take a slanted photo when you are using a mobile device, and it was something we had all encountered. We even had a couple of prototypes built a few months back, in which you could manually change the tilt angle of photos by rotating a set of wheels, with different sensitivities. However, none of these prototypes felt as if they fitted in with the simplicity of Instagram.

While brainstorming with other engineers about ways we could include this feature in an Instagram-y way, one of our engineers had the idea that it would be great if we could automatically correct photos taken in the Instagram-app camera using data from the mobile device. After all, most phones have a variety of sensors that allow us to determine the orientation and tilt of the device relative to a specific reference, meaning we can tell the angle of your phone at the time you took the picture. This seemed to us a way of making the feature quick and simple to use, which is something we try to achieve with every feature release.

How does it work?

As I mentioned, most smartphones contain sensors capable of determining the orientation and tilt of a device. When you take a picture in-app and tap on the new straighten icon, we use this sensor to straighten the photo automatically. In order to correct the angle, we rotate the photo by the opposite of the angle in which you held your device. Once the auto correction is applied, you can fine-tune the results using the feature’s UI.

You may notice that while the photo is being rotated, we need to zoom in a little. This is due to the fact that when we rotate the photo, there would be empty regions at the corners if we didn’t zoom in. You can imagine having two square pieces of paper on top of each other:

If you rotate the topmost one, you’ll start seeing the edges of the one underneath as you rotate the one at the top. Now, if the topmost paper is your photo and the bottom one is our app “window” you’ll see that we need to “fill” the edges by actually making the photo larger as you rotate, up to the maximum possible scale, which would be the square root of two (~1.4142). The maximum zoom would occur when the photo is rotated at 45º. In reality, however, if you actually took a photo in a 45º degree angle, it is most likely that you wanted it to be that way, so we only magically straighten photos for up to an angle of 25º

Designing for Simplicity

Once you enter the straightening mode, you will notice how the photo is auto straightened in an animated way; when you tap the button the photo is rotated and zoomed in before your eyes. This animation turned out to be a very important piece of the puzzle as it helps the user understand what is happening to the photo. When we first tried the animation it was almost a “eureka” moment; it made the feature appear magical, while easily explaining all the different pieces at play in the interface.

Once the animation is done, and in case we got the angle wrong, or in case you are simply feeling creative, you can still manually rotate the photo by dragging the wheel at the bottom of the screen. We added in other gestures for people looking to really fine-tune their pictures: if you tap on the edges of the wheel you can rotate by 0.1 degree increments. There are also two other ways to rotate the photo by using common iOS gestures: two finger rotation, or even one finger rotation, for easy interaction with just one hand.

We believe the final result really fits with the overall goal of simplicity and performance, and adds to the Instagram experience: help you take beautiful photos in a simple and delightful way. We are excited to get this feature into the hands of all our users, and listen to their feedback. As with everything we build, we look forward to seeing our community get creative with this new feature.

— Alex Restrepo, iOS at Instagram