Tag Archives: Perspective

SKRWT: A Necessary Tool

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.

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!

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.

The SKRWT app is currently $1.99 on iTunes. You can find out a lot more about the app on the SKRWT site. It is designed for the iPhone, but runs with no problem on the iPad.

This is one of those apps you absolutely need on your iPhone. Worth every penny.

Perspective Correction Comes To The iPad

For a long time I’d been hoping for a basic perspective correction tool for the iPhone or iPad. I’d shown one way to do this on the iPhone in the past, but a new app has arrived for the iPad called AndifTouch.

AndifTouch GUI

The main GUI of AndifTouch on the iPad.

The description from iTunes is very minimalistic. “AndifTouch is an app to interactively adjust radial and perpspective distortions in pictures. Radial distortions are typical for wide angle photography. Perspective distortions (keystone effect or in german: Stuerzende Linien) occur often in architectural photography.”

I explored the app and found it does exactly what it says. Overall I really like the app, although in this version 1, there are some things that need improvement.


  • Allows for easy movement (scale, rotation, and shift), perspective, and distortion using just dragging gestures on the photo
  • Grid is helpful
  • Exported images are at full resolution (at least up to iPhone 4S resolution)
  • Help is very straightforward


  • The GUI for the cropping tool needs improvement.
  • Not sure why the “spinning” logo is always visible.
  • On a few occasions I got a “not enough memory” message when trying to save an image. It seems to have always exported, but the region in the app that showed the image is now black.
  • The grid is visible on the exported image if you leave it turned on. Not sure if this is a bug or not, but I can’t think of a reason for it.

Things I’d love to see in the future:

  • Ability to increase number of grid lines (such as is done in Image Straightener)
  • Change the crop tool so that you have an autocrop button, and also a more traditional view as in Camera+
  • A preference for whether you want everything to reset when you import a new image (currently all settings are saved).
  • A numerical display of the current settings.
  • A reset all button (move, perspective, and distortion)

Here are a few before/after samples which I used in my video walkthrough on YouTube (note: no audio, this is just raw recording from my iPad).

Before/After photos using AndifTouch

Using AndifTouch. The photo on the left is uncorrected. The photo on the right is corrected. Notice that posts are vertical and parallel to each other in the final image.

Before/After photos using AndifTouch

I used AndifTouch on the upper photo. The final output is the lower photo. Note the building now has “right angles” where it should and the umbrella and phone pole are vertical.

I really like this app and hope that the developer continues to improve it!

Currently AndifTouch for the iPad is $0.99 on iTunes. [download]

Perspective Correction on the iPhone

Although I rarely use it, every now and then I want to do a bit of perspective correction (or perspective control) with my images. In Lightroom I’d gotten used to using the perspective correction feature, but I hadn’t yet seen anything like this in any photo apps that I’d liked*.

If you aren’t familiar with perspective correction, it basically means adjusting the image so that lines that are parallel in the real world stay parallel in the image. Your eye and mind are very good at “perceiving” parallel lines, but cameras can’t do that, so anytime you are not pointed directly at the main plane of an object (such as directly above a piece of paper), the perspective won’t be ideal. These images give you a quick idea of what this means.

Typical snapshot with no perspective correction.

Typical snapshot with no perspective correction.

Snapshot after perspective correction.

Snapshot after perspective correction.

In the left image the sides of the building seem to slant towards the upper middle portion of the picture. When viewing the actual scenery your mind knows that the sides of the building go straight up and it perceives it that way. To make the snapshot show what your mind perceives you need to do a bit of correction. You’ll then end up with the image on the right.

It almost looks as if the camera was moved up in to the sky so it is sitting right in the middle of the building. This is a correction to the perspective (or view).

Can you do that on the iPhone/iPad? In an email exchange with the developer of the Image Straightener and Image Blender apps (both superb apps) he pointed me towards JotNot Scanner. This app is for the iPhone (runs fine on my iPad 2) in the business/productivity category, but it turns out it is useful in photography.
Continue reading