Preserved Topic: Correcting pincushion and barrel

This is one I have been hanging on to for a long time. Only one other person knows about this (Steve), and I figure it's time to finally share. Some history behind this, but I'll spare you folks - I'll do my best to keep the rambling down to a minimum.

Barrel distortion and pincushion distortion can really suck. It's a photography thing. You can get plug-ins or stand-alone programs to correct this, but it's time for Displace.

Here's the D-Map in a nutshell:



1) This is channel one. In my case: Red.
2) This is channel two. In my case: Green.

Use your favorite gradient methods to create those. I did mine by filling with Black, then using Circular Grad set to Screen. All four corners are White and the middle is Black. Then I used Levels to bring the Black point up to Grey. Then I selected the appropriate half and Image > Adjust > Invert (ctrl + i). I also had some help from Grid.

3) Add a Curves Adjustment Layer like so. Pardon the sloppiness of my free-hand skills. Those should be perfect 1/4 circles. The better your Curves, the better your results.

4) Composite. I do my D-Maps in RGB and I fill the Blue channel with 50% Grey. This is what it looks like by the time I save.

Grab your problem photo and start using the D-Map. Use Stretch to Fit and make sure you use the same value for Horizontal and Vertical. Positive values will fix one type of distortion and negative values will fix the other.

I've tested this quite a bit with quite a few problem photos I've found on the net and it worked like a charm every time for both types of distortion. Even worked like a charm for photos with non-1:1 ratios.

Tada.

I'd really like to see a before and after.


[dis]contempt+[.org]

Yup. Sounds great, but examples would go a long towards conveying exactly what the need/benefit of this would be.

No examples from me this time around. I developed this technique a long time ago (seems like forever ago), and I didn't archive a damn thing. The only thing surviving from those days is a little piece of paper with a doodle on it describing how to make the D-Map.

If you want to play, try Google with "pincushion barrel distortion". Should pull up some good pics to play with.

Barrel Distortion is one. He's got some monster pics to play with. Looks pretty tasty.

So, there you have it for the truly inquisitive.

That`s pretty slick, WJ. What else are you not telling us ? Hhhmmmm?

Only thing ..it seems too pull the corners more than the center. Have I just not found the magic number yet, or did I botch the Map ?

This , along with the other Cubes, make a great drawer in the tool box. Really good stuff.

<edit>Stupid Fingers</edit>

Cell245

[This message has been edited by docilebob (edited 07-16-2002).]