Monday, March 21, 2011

Ultra-Wide Distortion Fix

In my "Battle Of The Super-Wide" post, I show you a picture of the New Zealand Old Government Buildings with the "Beehive" at the foreground.

The picture was taken with my 114° Panasonic 7-14mm f/4 ASPH LUMIX G VARIO which I use on my Olympus E-P2 m4/3 camera.

The lens exhibits the classical "leaning building" symptom of a ultra-wide lens, and I promised;
"In my next post I will show you how to correct this shortfall."

According to Wikipedia:

An ultra wide-angle lens is a lens whose focal length is shorter than the short side of film or sensor.
Thus the term denotes a different range of lenses, relative to the size of the sensor in the camera in question.
  • For APS-C any lens shorter than 15 mm is considered ultra wide angle.
  • For 35 mm film or full-frame sensor any lens shorter than 24 mm
  • For 6x45 any lens shorter than 41 mm
  • For 6x6 and 6x7 any lens shorter than 56 mm
So I suppose my Panasonic should be known as ultra-wide!

Ultra-wide lenses are hard to use, I talk about it here and Ken Rockwell has written a nice guide too.

But today we are talking about correcting the "leaning building" effect, this distortion happen when you tilt your lens while photographing tall buildings; let's take a look at options to remove this distortion!

Lens Correction in Adobe Camera Raw

Adobe Camera Raw is a post digital image processing software from Adobe. It can open and tweak virtually all RAW format produced by differnt digital cameras.

Since I took my shot in RAW format, I will try to correct the image before I open it. This is what it look like within ACR.

Before tweaking in Adobe Camera Raw.

This is the setting I used in ACR, notice I scaled the image to 77% for this adjustment; without which, you cannot see what is actually been cropped away.

How it look like in ACR before cropping. Notice the part that have to be discarded, that is the price you pay in straightening the affected buildings!

This is the corrected picture. Notice the building are no more leaning and the perspective look about right. Too bad some part of the picture had to be cropped.

Overall, I find Adobe Camera Raw quite easy to use. But you must shoot in RAW format though!

Filter > Lens Correction in Photoshop

"But with jpeg, I can do that in Photoshop what!" My cleaver photographer friend commented. Yes, you can! Lets take a look...

This is what it look like if you go to "Filter" then "Lens Correction" in Photoshop CS5. Forget about "Auto Correction" and select "Custom".

I suppose you can see that lens correction in Photoshop is more intuitive, it came with a grid feature which is extremely useful in monitoring the verticals. The only downside is the "angle" dial which is over sensitive, this has the same function as "rotate" in ACR.

I found I had to go 100% in the "Vertical Perspective" to straighten the building. The picture was scaled to 50% with the "scale" slider.

The corrected picture after cropping and "flatten". How does it compare with the one in ACR?

As you can see, both gave about the same result. Somehow, the one that was done in Photoshop look more "stretch" than the ACR version!

What if...

What if you do not have or cannot afford Photoshop and you prefer not to shoot RAW, is there a software program that allow you to correct perspective distortion in ultra-wide shots?

YES! PTLens!


PTLens is a small software that corrects lens pincushion/barrel distortion, vignetting, chromatic aberration, and perspective. Both PC and Mac users are supported.

PTLens was written by Tom Niemann of, Portland; Oregon in 2002. It started as a DOS command line application!

I was using PTLens in 2006 to correct pictures I shot with my Canon 15mm fish-eye, I had to do it in Windows machine because there was no Mac version.

I remember emailing Tom...

"Hi again
Ever thinking of doing a version for Mac OSX?
Were u involved with the CS2 lens distortion plug-in?
Regards - CY"

He replied...

"I estimate about 4-6 months work to port to a MAC. No plans to do so currently.
Not involved in the lens distortion feature in CS2, but suspect they got their idea from PTLens."

That was FIVE years ago :)

Last week, I visit PTLens again and was ecstatic that this incredible software now support OSX 10.6 and it also came with:
  • Standalone application (JPEG, 8 or 16-bit TIFF, Raw)
  • External editor for Lightroom/Aperture/iPhoto (JPEG, 8 or 16-bit TIFF)
  • Plug-in for Photoshop (any 8 or 16-bit RGB image, Photoshop CS3 or later, PSE 6 or later)
  • Plug-in for Aperture (JPEG, 8 or 16-bit TIFF, version 2.1 or later)
All that for US$25.00!

You can go to his web site and view examples of PTLens at work, watch a video of PTLens in action, and download the software for a free 10 image trial.

If you like it then you can purchase the license for $25 and activate the software permanently.

Before and after adjustment in PTLens. Notice there are more sliders and more way you can fine tune your image. This is the interface of the stand alone app, you can then open the tweaked image in the image app of your choice.

I personally think PTLens did a more natural tweak than Photoshop and ACR.

PTLens also consists of more than 2,400 separate calibrations (cameras and lenses) — far more than any other application!

Below are some pictures I tweaked in PTLens, tell me if you like the untouched copies better :)
Pictures were all shot at St. Peter's Basilica, Vatican City, Italy with the Panasonic 7-14 and E-P2.

After trying to straighten the pillars, see how skinny the picture became! I rather prefer the untouched version. After all, that is the beauty of an ultra-wide lens ;)

You can even use PTLens as a creative cropping tool!

One job PTLens do very well is removing barrel distortion in shots taken with fish-eye lens.

These under the board walk ducks were shot with a Canon 15mm fish-eye lens at Granville Island, Vancouver; Canada. Barrel distortion exhibited by the lens were removed with PTLens.

Famous Last Words...

During my travel I do not have much time to spend in composing my pictures, that is why an ultra-wide is very useful to capture the scenery first and when I come home I can crop and improve my shots.

Lens correction is part of my work flow.

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