Help on correcting Barrel distortion

P
Posted By
Phosphor
Jul 2, 2003
Views
116
Replies
7
Status
Closed
While my G3 is fine for most things, the lens (as is typical of zoom lenses, particularly on compacts) does have quite noticeable barrel distortion at extreme wideangle (and less extreme pincushion at full zoom)

On architectural shots I prefer my walls straight to bendy!

Anyone know of a cheap (free if possible!) Mac OSX solution? A trick in Elements, or a plug-in- a plug in that actually runs in Elements in classic mode would be OK.

(Panotools can do it, but it crashes Elements and the system in Classic mode, and I hate to reboot into OS9 just to fix one picture!)
Susan S

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P
Phosphor
Jul 2, 2003
Susan,

Other than Panotools, I don’t know of any free plugins but you can do a quick and dirty job using the spherize filter.

1st, increase the canvas size by about 50% in both directions (make sure the anchor point is the center box). There is a "percent" entry in the dropdown that makes it easy.

2nd, filter->distort-spherize

Set mode to normal and adjust the amount to correct the distortion — plus to correct pincussion, negative to correct barrel. The amount will depend on your lens and the zoom setting but it shouldn’t be too large.

3rd, crop to desired size.

You may need to adjust the canvas resize percentage to move the correction to the corners of the image or to fine tune the effect. Click on the "-" in the spherize dialog to zoom out enough to see the whole photo.

It’s not perfect by any means but it does have the advantage of being free. Try it and see if it works well enough for your purpose.

Bob
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Phosphor
Jul 2, 2003
Thanks Bob – that’s a suggestion I hadn’t seen. I’ll give it a try. Susan S
CS
Chuck Snyder
Jul 2, 2003
Susan, lots of references in Google (‘correcting barrel distortion with Photoshop’) – here’s one that looks pretty simple:

http://www.bythom.com/distortion.htm

Chuck
RR
Raymond Robillard
Jul 2, 2003
Pete,

You’re right. There’s one image just like that on the website of a competitive product of Elements. They claim that the perspective correction does wonders, but when you look at the picture, it’s odd in some way.

Ray
P
Phosphor
Jul 2, 2003
Susan,

Panotools has a reputation for being crash prone so it’s not just you. I tried it a while ago and it crashed my system so I don’t use it. That was under Windows 98, I’m using XP now but haven’t tried it again and I haven’t checked to see if there’s a newer version out. I hadn’t heard of PTLens. Maybe I should take another look at Panotools.

I see Chuck has been busy! Lot’s of helpful people here! His first reference is basically the same technique as what I gave only they use a smaller increase in the canvas size. That amount (25%) doesn’t come close to reaching the corners of my photos and doesn’t do a good job of matching the curvature. I’m lucky, my camera lens doesn’t show much distortion and I’ve been able to correct it fairly well with that technique using 50% and settings in the -5 to +5% range. Distortion varies with focal length but it’s different for each lens design. The old caveat applies: your milage may vary.

The LensDoc program from Andromeda mentioned in Chuck’s second post works well but it’s a bit pricey, around $90 US if I remember correctly. Too rich for my budget.

Thanks for the reference to PTLens.

Bob
CS
Chuck Snyder
Jul 2, 2003
Susan, do you have a hyperlink for PTLens? Not having much luck locating it…

Thanks, Chuck

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