Perspective
and Barrel Distortion Correction of Wide-angle Images in
Adobe Photoshop
This image was shot in the "Desert Passage" shopping area of the Aladdin Hotel in Las Vegas.
It was shot with a Nikon CP990 digital camera with the equivalent of a 24mm wide-angle lens on a 35mm camera.
Since shooting position was restricted, the camera was tilted producing a strong keystone effect. This tutorial deals with fixing it.
Rotating
A grid is an invaluable reference in this process.
Select the grid via the "View" menu.
The width of grid can be adjusted under the Edit menu in Preferences > Guides & Grid
On the tool palette, select the Measure Tool. It shares a block with the Eyedropper and Colour Sampler tools, so it might not be evident.
Click on the little triangle in the lower right of the square and select it.
Find a line as close as possible to the centre of the image and draw along it with the Measure Tool.
Select Image > Rotate Canvas > Arbitrary and the necessary amount and direction will come up automatically. Click OK.
And here is the image rotated.
Ignore the corners for the time being.
Perspective Correction
Under the Edit menu, choose Transform > Distort.
Pull the square "handles" until the lines in the image match
the lines in the grid and the objects are in the right proportions.
When all is to your satisfaction, double-click within the image or hit the "Enter" key.
Barrel Distortion
Photoshop 6.0 has a filter under Distort, called Spherize that allows a negative value to be input. I have found it to be ineffective, and have not found any other means of correcting barrel distortion. If I do, I will certainly update this site. In the meantime, I highly recommend the "Warp" tool in Paint Shop Pro.
Andromeda Software, Inc. does sell a third party plug-in "LensDoc" that is reputed to be able to do the whole process of perspective and barrel distortion within a single interface. I have not yet tried it, so can not yet recommend it. I do understand it has a fine reputation however. If I get a chance to try it, and find it satisfactory, I will update this site with reference to it.
For further discussion please go to any of the following forums that I frequent:
Yahoo! Groups PhotoGallery - http://groups.yahoo.com/group/PhotoGallery
Yahoo! Groups Coolpix990 - http://groups.yahoo.com/group/coolpix990
Yahoo! Groups nikon5000 - http://groups.yahoo.com/group/nikon5000
Yahoo! Groups digital-darkroom - http://groups.yahoo.com/group/digital-darkroom
