© Jan Esmann and Power Retouch. All rights reserved.

Photoshop plug-ins for retouching

Lens Corrector

Quick introduction

This Photoshop plug-in lets you correct pincushion and barreling lens distortions. Either symmetrically or arbitrarily (sides unevenly distorted). It also corrects some panorama photos. This is the Lens Corrector plug-in’s control panel. Click on the image for a larger view. It works with the following image modes: 8 & 16 bit/channel: RGB, CMYK, Grayscale, Duotone, Lab.

What is lens-distortion?

Camera lenses, in particular zoom lenses, produce some kind of distortion. The two classic distortions are pincushion and barreling. But if you crop either of them, or held the camera at an oblique angle to the parallel lines, you get what we call an arbitrary distortion.
Pincushion
Barreling
Arbitrary

General settings

First you get to decide if you want some sharpening of the output image or not. Next you can determine how the plug-in should interpolate the new values. It can weigh the interpolation towards the average (mean) or median. You can of course let the plug-in decide and set it to auto.
Sharpening menu
Interpolation menu
Zoom to fit  will crop the images to the innermost edges of the corrected image. If you turn it off, you will have some unfilled ares which will be filled with white. It is generally convenient to leave it on. Mean is the traditional way of interpolating, but it produces a somewhat blurred result. Median produces a sharper result than mean. It is slightly slower, but the result is worth it. Auto will let the plug-in decide while it prioritizes median.
Before
After

Examples of symmetric

distortion

Notice in the corrected image, that not only are the columns straight, but the perspective in the floor is also correct. You can see it on the black footpanel in the bottom left side
In the examples below we corrected a distorted photo with our plug-in and with an algorithm that is freeware on the internet (Bourke) used at the faculty of astronomy at Swinborne University http://astronomy.swin.edu.au/~pbourke ). The problem with Bourke’s method, and most other commercial correction methods, is the exploded corners. Power Retouch invented a way to avoid these.
Bourke
Power Retouch
Original photo
Curve = 0
Curve = max

Curve

In general leave this at 0. As you can see from the two red grids curve settings produce different corrections. The higher the curve setting, the less the centre is affected and the more the corners are. Different lenses and different lens setting produce different curves. 0 is the most usual, but sometimes higher settings are needed.
Also note that the corners are not exploded. We will illustrate this in the next example.

Arbitrary correction

Here you have the same barreling and pincushion controls as with symmetric, but now they are specifically either horisontal or vertical corrections. Down <-> Up  shifts the centre of the correction from the bottom to the top. Left <-> Right  shifts the centre of the correction from left to right.

Panorama

Here we have a photo of a building taken with a panorama lens. Below we have the version corrected with Power Retouch.