Correcting barrel distortion and pincushioning?

[Player_1]

I recently read about barrel distortion and pincushioning. I didn't know there were terms for the things I saw in my camera pictures.

What I'd like to do is straighten-out the pictures I have in a program. I don't know what program to use, except GIMP. And I don't really want to spend any money doing this.

Does anyone know a free program I can use to correct pincushioning and barrel distortion?

 

[Digital Matt]

http://epaperpress.com/ptlens/

 

[Player_1]

I looked at that a few times before I came back to this thread. That progam only allows 10 images.

I need to do more than 30 images.

 

[Digital Matt]

The license is $15.......

 

[surge]

i take quite a lot of architectural pictures and with my old camera the barrel distortion was quite bad at the wide end of the zoom, exactly where i wanted to be for photos of buildings, and often quite noticeable in the end image. so i read up on a technique of correcting the image using photoshop.

(i've never gone to the bother of correcting people - if you want to try though please tell me how successful it is)

i'm not sure about the commands/tools for gimp - i've v. little experience with that package - i only just downloaded it and haven’t had time to try any manipulation yet but it should have the ability to do the job.

i'll explain using the relevant photoshop terminology and hope that translates ok:

and if your image has a level horizon + is taken straight on to the subject that will help a good bit first time round...


to correct for barrel distortion at the wide end of a standard zoom lense:
1. turn on a grid overlay (view, show, grid)
that should help you see where your image is distorted and get a handle on how much your affecting it in the next steps, but make sure that snap to grid isn’t turned on.

3. select all your pixels (Ctrl + A)

2. apply the spherize filter [which looks like it was created for making images into pseudo fisheye] with a value of approximately -6%. (filter, distort, spherize) [depending on your lense/camera and how far your zoomed in/out]

3. adjust the perspective, (edit, transform, perspective) by dragging the top corners of your picture horizontally towards the middle of the image; only a small amount.

4. crop the edges you've moved to be square again. (select pixels to keep, image, crop)

Hints.
-the trick is to try and straighten up the images horizontals with stage 2, and then correct the verticals of the image with stage 3, referencing to the grid of course.
-if the subject isn’t centred or the perspective is asymmetrical then adjust the image’s perspective in stage 3 differently for each side [top corner] to compensate using (edit, transform, distort)

and the finished result - http://www.thephotoforum.com/forum/showthread.php?t=69905

Hope that’s alright for you, it honestly doesn’t take me that long… not as long as writing out the instructions anyway! And show us how you get on.