It took awhile before the first few perspective correction apps were released for iOS, but last year SKRWT was released. It’s one of those apps that as soon as you use it you’ll know you can’t live without it. The description starts out as:
No more crooked lines! This keystone and lens-correction tool turns your phone into a view camera. All hail symmetry.
CORRECT LENS DISTORTION
Converging lines have always been a given in iPhoneography due to the fixed focal length of today’s mobile phones – but not anymore. You can now correct horizontal and vertical perspective distortion with just one swipe. It’s really that simple!
ALL-PURPOSE LENS CORRECTION
If you have been using any adapters for your mobile phone – from wide-angle to tele-zoom or external cameras with wifi-connection – you now have your all-inclusive distortion-correction with you at all times.
Let’s just say I could live with just those features, but the list is far more extensive. If you want to know how important lens distortion can be, and what this app can do for you, spend a few minutes watching this video.
I always have a tough time remembering the name of this app, but based on the spelling I mentally use ‘screw it’ as the name when I use spotlight to find the app. I figure I need to twist (screw) the image to correct it. A screw is also a simple machine on wikipedia, and this app certainly makes it a simple process to correct image distortions.
This is one of those apps you absolutely need on your iPhone. Worth every penny.