Tuesday, January 17, 2012

Photoshop #2 - How to correct vertical lens distortion

Image taken at street level has visible vertical convergence

We've all been there, out and about walking (or driving as was the case above) around town and we see it, a tall building or structure that stands out and we want to capture it's vastness. As was the case for me in the image above the Financial District of Boston demonstrates what we end up with due to perspective of the lens to what it is shooting is tall lines of the buildings converging together at the top of the photograph as if falling towards each over as the buildings height increases.

Those of you who are fortunate to have a small fortune to spend on such equipment as a tilt-shift lens don't need to worry about such concerns. Such a tool mechanically alters the plane of the camera's lens to match the perspective of the building thus preventing those converging lines, if however you are like me you will have to rely on post processing techniques to deal with such problems.

How to correct vertical lens distortion using Photoshop

The steps I describe are from my using Adobe Photoshop CS 4 however other versions have supported this function I believe for some time as to other software packages.

Step1 Take a copy of your original image and open it in Photoshop, this is so any changes we make do not effect the original which you can always refer back to and start again if the worse should happen during any editing.

Lens Correction 'Filter' in Photoshop

Step2 Select Filter>Distort>Lens Correction to be presented by a range of useful adjustments that can be made.

Image with vertical perspective now corrected

Step3 Photoshop has provided a grid overlay for us to judge how best to apply our correction, the one we are interested is under the 'Transform' panel, slide the 'Vertical Perspective' slider to the left slowly until the vertical edges of the predominant buildings/structures of your image are aligned with the overlay grid as shown.

Due to the correct we have lost parts of the image as shown

Step4 Once you have adjusted to the correct perspective click 'Ok' to exit Lens Correction but before we call our job done you will have noticed you have lost some of the image at the top and gained white space towards the bottom. Using the crop tool select the area of the photograph that affords the most pleasing ratio while still allowing the white space area to be cropped out as shown below.

The final result

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