If you've ever shot a photo of a tall building from the ground, you know when you tilt up at it, the perspective goes wonky and your beautiful square building starts to look like the pyramids of Egypt.

SKRWT by mjagielski [$1.99 on the App Store] is an app that makes correcting that perspective distortion extremely simple. Not only does it do keystone correction, but it can also fix wide angle lens distortion. 

To use the app, just select any photo shot on your iPhone or another camera that you've transferred over, choose the appropriate distortion correction type, and start dragging on the control slider. In the screenshot below, I picked a vertical perspective correction. As you roll over the screenshot to see the before and after, notice not only the change in the image, but also in the readout at the bottom of the image. This image was shot on the iPhone.

In SKRWT, the before and after of a perspective-straightened bridge

You may have noticed that the top of the bridge has been cut off. When you're distorting the image that much, you're bound to lose some data from the edges. So when shooting, if you know you're going to be correcting the distortion later, be sure to shoot with some extra padding so when you make the correction, you don't trim off anything critical. That said, the app does actually retain all the original data so you can crop around the blank edges manually if you don't mind changing your crop ratio. When starting, SKRWT maintains your original aspect ratio, but a trip to the crop tool reveals that you can re-crop your photo to hold on to the most important parts.

The crop tool reveals that all the original image data is still there; you can manually crop around the empty areas if you don’t mind changing the crop ratio

Here's another before and after. This photo was shot on a LUMIX GH4 and transferred via wifi to the iPhone. It was fixed using both keystone correction and rotation.

This image was keystone corrected and rotated using SKRWT

This is a great tool to add to your iOS arsenal. Whenever you have an image that is just begging to be “true”, fire up SKRWT and straighten away!

SKRWT by mjagielski
$1.99 on the App Store
Screenshots with Version: 1.1.1, iOS 8.1.3, iPhone 6 Plus