Fixing Corner Vignetting

I have a shot taken with a view camera and I tilted too much cutting off two corners. Didn`t Marc Muench have an article in Outdoor Photographer on how to fix corners using the Gradient tool? Could someone point me in the right direction on how to do this?
Mike Sellers

I don't know about an article, but here's how I'd do it assuming you start with a single layer image in PS...

1) Create two levels adjustment layers - there will be layer masks with both.

2) Apply the gradient tool in the linear gradient mode (straight line gradient? not sure what it's called) and create a gradient in each layer mask in the vignetted corners. Make sure the gradient tool is set to black on one side, and white on the other, and make the gradient so that most of the mask is black, and starts fading where the vignette starts, fading to white right in the corner. (Sorry if that's hard to visualize...) One layer mask will have one vignetted corner white, and the other layer mask will have the other.

3) Adjust exposure in the two levels layers using the levels controls. The layer mask will keep the main part of the image the same, and fade the amount of change in the corners, emulating a reverse vignette.

OK - I was thinking about this more, and you might also be able to get the gradient tool to do both corners at once using the "circular gradient" mode if you play with the customizations available in the gradient tool. Then you'd only need one levels adjustment layer. That would also have the advantage of having a rounded gradient into the corners, if the straight line gradient I mentioned above is obvious in any way.

Filter->Distort->Lens Correction has a vignette adjustment window that adds or reduces vignetted corners quite well.

Mike, the process John mentions is the one I have used often. Depending upon how bad the corners are might be an issue with that process. If not then the gradient approach David has outlined would be yet another avenue to try. Good luck!

The problem with John's method is that it will apply the "fix" to all four corners, whereas the problem in this situation only affects two. David's gradient fix will probably be more appropriate.

Actually, using that Lens Correction method and then using a Layer Mask to 'erase' the effects where they aren't needed would work, wouldn't it?
Also, if you have CS3, you can use the Lens Correction method as a Smart Filter, which will allow you to return at any time to re-tweak the correction.

Thanks for the tips-I should be able to get it fixed now!
Mike

I started to try the Filter-Distort-Lens Correction method but it isn`t available on my version of photoshop - CS -it must be on CS3? Oh well.

I don't have all the fancy tools in CS3, but here is how I would do it using PS7. Use the eliptical marque to select the portion of the image not needing correction, CTRL-I to invert that, then create a curves layer and lighten the selection. Then ALT-click on the mask, paint black in the 2 corners you don't need to change, ALT-click on the mask again, then blur to taste. This may take a few tries to get the elipse in the correct location, but it works quite well. This is the method I use to do the opposite and purposely vignette my images.

The problem with that Adam (and it might be really really minor - I can't try it right now) is that real light fall-off vignetting gradually gets darker toward the corners. Hence the need for gradients if you're a real stickler about it. What you're suggesting would apply a change from your selection to the corner without changing along the way.

Of course, like everything in PS, if it works for you, then it's the right answer!