SKRWT is one of those apps which you don’t know you need it until somebody point it out to you.  The app does a few specific things and does them very well.  It will fix your photos from something that is called, according Mathäus Jagielski the app’s creator, the Keystone Effect.

What is Keystone Effect?

You’ve seen this many times especially when you use a Projector to project something to a surface (normally a wall or a screen) but you have to do it in an angle. The resulting projection will normally get distorted, the dimension of the image is skewed, making it look like a trapezoid.

This ‘skewed’ shape is typically called Keystone Effect (apparently because it resembles the shape of an architectural key stone). To fix this, to make the image rectangle or square again, usually the device provides some way to correct it, using some kind of Keystone Correction control/tool.

SKRWT is the equivalent of this tool but for your digital photos.

Apart from the Keystone Effect the app will also fix other type of effects (or defects?) namely Perspective and Barrel Distortion

What is Perspective Distortion?

In Photography, you can also get Keystone Effect when we, let’s say, want to take picture of a very tall building and we don’t have much space to back up to. So in an effort to take as much as we could in one frame we usually tilt our camera up. The combine result of this close proximity to the object and the angle to where we point our camera create the phenomenon the is also called Perspective Distortion.

Have a look at some example of photos I took below. What do you think is wrong with these photos? YES, all the vertical lines (e.g. of the buildings) seems to be skewed and are not as straight as they should be in reality, just like that Keystone Effect we get from the Projector!

No worry, soon we will fix this with SKRWT!

What is Barrel Distortion?

Another thing that SKRWT will fix for you is what is called the Barrel Distortion.  This type of distortion affects mostly when we use Lenses that has wider viewing angle than the normal 35mm lens (i.e. with a focal length less than 35mm).  This will include all Wide-Angle type lenses, Fisheyes and surprise surprise the iPhone Lens.

You might not know this, but the iPhone 5/5S camera lens has a focal length of about 33mm, whilst the iPhone 4 lens has about 29.4mm. So, in reality the iPhone lens can already be categorised as a wide-angle lens. This is why when we take a photo with an iPhone, we can actually fit in more in the frame compared to say a regular 35mm pocket camera.

That’s one of the advantages of having a wide-angle type lenses. The drawback is that the resulting image is distorted. A typical image captured using a wide-angle lens would have objects in the middle seem to be magnified or inflated as if they have been mapped around a sphere (or a barrel). The curving effect gets worst toward the edge of the image, especially when we use Fisheye lenses.

The iPhone camera lens, being a wide-angle lens itself, is also prone from this distortion though not in a big way. But when you use one of those wide-angle of Fisheye conversion lens, you will definitely get this effect.

Again, with SKRWT app you can correct this distortion in no time.

SKRWT with it!

Now let’s dig deeper on what SKRWT has on offer.  The following list contains all the tools you can find in the app.

  1. Keystone Correction.
  2. Skew Correction.
  3. Barrel Distortion Correction.
  4. Straighten.
  5. Rotate.
  6. Manual Crop.
  7. Auto Crop.
  8. Vignette Correction.
  9. Grid Control.

You can either take a photo directly from SKRWT or load a photo to edit from your photo album. Once you load the photo you can start edit it with one of the above tools.

Each tool is represented by an icon and these icons are arranged on the ‘rotating ribbon’ at the bottom of the screen. I said rotating because when you reach the end of the row, it starts from the beginning again, ad infinitum. It’s a cool user interaction ‘trick’ I’ve never seen implemented in other app before. Finally, to use one of the tool, just tap on the icon, which will bring up the ‘edit screen’

Each of the edit screen, with the exception of the Rotate, the Crop and the Grid control, will have a dial at the bottom. You can swipe left or right on the dial to make changes to the photo.

If swiping left or right affect to much changes for your liking you can go more precise by tapping the left or right edge of the ribbon. Each tap will affect one bar at the time.

Lastly you can also double tap the ribbon to reset the ribbon back to zero position.

Let’s have a look at each of these tools in a bit more detail.

Keystone Correction

Of all the 3 correction tools available in SKRWT, Keystone Correction is probably the one the you will use the most. This is because most skewed photos we take would suffer from the Keystone Effect. As I explained earlier, these are the shots you usually get when you point your camera in an upward angle.

Let’s take an example of this shot I took.


Now let’s correct it using SKRWT Keystone Correction tool.

SKRWT - Precision Dial in the Edit Screen

Choose Keystone Correction Tool

SKRWT - Correcting Keystone Effect

Swipe or Tap the dial to correct


Here are a few more.

Skew Correction

The second tool you can use with SKRWT app is what I call the Skew Correction tool. I must admit, I couldn’t find many shots I took that needs to be corrected with this tool. In fact I could only find one in my album.

As you can see from the shot above, the building I captured was a little bit skewed, let’s see if we could fix it.

SKRWT - Skew Correction Tool

Choose the Skew Correction tool

SKRWT - Skew Correction Tool

Swipe Left or Right to affect changes

And there you go!

Barrel Distortion

As I explained earlier Barrel Distortion is the type of effect you normally get when you use wide-angle lenses (smaller focal length), which actually includes standard iPhone camera lens. The smaller the focal length of the lens the bigger effect the photo would get distorted. That means lenses like Fisheyes will be affected the most, as you can see from these sample photos I was showing you earlier.

No worry, we can correct it with SKRWT app.

SKRWT - Barrel Distortion Correction

Choose the Barrel Distortion Correction tool

SKRWT - Barrel Distortion Correction

Swipe left or right on the dial

Not only that the wide-angle lenses will give you Barrel Distortion, they will often give you the Keystone Effect too. But we know we can fix that straightaway.

SKRWT - Keystone Effect Correction

Choose the Keystone Effect Correction tool

SKRWT - Keystone Effect Correction

Swipe left or right on the dial


Here is one taken with a Fisheye lens.

SKRWT - Barrel Distortion Tool

Choose the Barrel Distortion tool

SKRWT - Barrel Distortion Tool

Correct the distortion

SKRWT - Keystone Effect Tool

And fix the Keystone Effect

Auto and Manual Crop

Now let’s talk about other non-correction tools that SKRWT also provides, starting with the Auto Crop. The Auto Crop, which is turned on by default, allows you to automatically crop the edited photo every time some type of correction process is done. It’s hard to explain without actually seeing it in action, but have a look at the following un-crop image that I’ve been edited previously. You can see that all the edges are skewed here and there due to the edit process. Typically I would have to load it to the Manual Crop tool and crop it myself.

But with the Auto Crop on, SKRWT will try to analyse the image and take a calculated guess how the image should be cropped and do it for you, as you can see from the previous screenshots.

I’m very pleased to say that SKRWT has so far done a good job in ‘guessing’ the best crop for my edited images. Obviously if you are not satisfied with it, you can always fall back to the Manual Crop and do it yourself, especially if you want to crop in a specific aspect ratio.

Straighten and Rotate

These two tools are pretty standard in any good image editing tool. They do exactly what it says, to level and rotate your image.
With the Straighten tool you will be able to rotate the image up to 45 degrees to the left and right.

SKRWT - Straighten Tool

Choose the Straighten Tool

SKRWT - Straighten Tool

Swipe on the dial to straighten

While the Rotate tool will allow you to completely rotate the image 90 degrees at a time.

Vignette Correction

The Vignette correction tool is an interesting one.  It will basically get rid off any Vignetting effect that your photo has.  The dial goes from dark to bright when you swipe from left to right.

SKRWT - Vignette Tool

The bright vignette

SKRWT - Vignette Tool

The dark vignette


Grid Control

Last but not least it’s the Grid Control. This tool allows you to change the appearance of the guidelines overlay for the image. You can choose how many lines in the grid and what colour is the line. Such a simple tool but I wish other app has this too.

Final Verdict

SKRWT is not the first app that tries to tackle these types of distortion. A couple of other apps have also similar features. Some of them are for example: