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I used the Tokina 12-24 quite extensively during my UK trip. It is a great lens, but like all wide angle lenses, it introduces significant distortion into images at the wider end of its range.

When photographing landscapes, this is not such a problem, but when photographing buildings and other structures, it can totally change their appearance.

I've been playing around with various Photoshop features to try to correct this, and thought I'd detail the technique that I've developed for others to try and comment on...

As an example, I started with this image that was taken inside Carnarfon Castle in North Wales at 12mm. As you can see, there is quite a lot of distortion...



After doing some initial processing in Camera Raw, I open up the image in Photoshop.

Before using Filter-->Distort-->Lens Correction, I increase the canvas size by 400 on all sides. If you don't do this, then Lens Correction will crop any areas of the image that move over the original boundaries of the image. By increasing the canvas size first, you preserve all areas of the image and can crop by hand later.



Using Lens Correction, I move the Vertical Perspective slider to -40, thus straightening up the verticals in the image. I also apply a -10 setting to both the Chromatic Aberration sliders to improve the blue and cyan fringeing.
After doing this, I end up with this image:



I then crop manually to a panorama format.



While this correction has improved the image, I find that the lens distortion has also compressed the buildings vertically and you don't get the sense of scale of this huge castle. In order to correct this I use the Scale function in Edit --> Transform. However, before doing this I increase the size of the canvas on the top edge so that the top of the picture doesn't get cropped off.



What do you think??? Does this set of manipulations improve the image?
Can you suggest other ways of approaching this, or improvements to my method?

John
Yes. Big improvement. However, I wouldn't do this to any image that you submit to the DPA to be used as forensic evidence.

Very interesting John and a good outcome.

Good technique John. Especially the point about enlarging the canvas before
starting. I use DxO Optics to do this same sort of thing. It has custom made profiles for various lenses so unlike PSCS it should theoretcially give a better result. But it doesn't have a module for the Tokina lens you have

I would be interested to know if there is any (more scientific) way of calculating the correction needed to the vertical perspective based on the focal length and/or distance from subject? If anyone knows, please tell

Thanks very much John !

Here is an example of your procedure:

before:


after:


Cheers,
CD

christiand wrote:Thanks very much John !

Here is an example of your procedure:

Glad you found it useful Christian

Leek,

this is going to sound stupid, but, is that Carnarfon Castle or Conwy Castle in North Wales? I've never been to Carnarfon Castle but have been to Conwy Castle many times.

If it is Carnarfon Castle then the interiors appear almost identical. It is a castle along with a few others I have wanted to see but never get the time when I'm over there.

Nice shots and the distort function is something I'm starting to play with more. It really is an invaluable tool.

Very impressive John, thanks for sharing

I normally use the distort transform tool in photoshop
i first place vertical guidlines along the verticals of the image as a guide
you can drag these from the rulers in photoshop

then you select all (selection tool)and use the 'edit' > transform > distort
this gives you 4 corner handlers to play with move these till you get the verticles near straight. Then horzintally compress the image to maintain proper proportion

in the examples shown above you have fixed the verticlas but the proportion of the height of the image is out of whack, try horizontally compressing the image by 6-10% that should make it look more realistic

the only issue with the automatic lens correcion tool is even when applied john the verticals on the left still look skewed, that's why the free distort tool is better because you can control the distort as much as you like.

good work anyway

Also a thing to note sometimes the 12mm distortion of builkdigns can make the scene look more dramatic, personally i like the 12mm distortion

Hi John,

did this as a manual distort in CS2 and added a Queensland Sky. What are your thoughts?

The skies in England / Wales around Dec/Jan are always blown, so I thought I'd add one in, hope you don't mind.

http://static.flickr.com/32/91654008_5e41ae6940.jpg?v=0

TonyH wrote:this is going to sound stupid, but, is that Carnarfon Castle or Conwy Castle in North Wales?

It's definitely Carnarfon Castle, because I didn't go inside Conwy Castle on this trip... They are very similar, but Carnarfon C is almost twice as big as Conwy C and is in much better condition. Well worth a visit...

I like the sky... I added a fake sky myself earlier when I was playing with PS, but decided it looked a little too surreal - I quite like it though...

stubbsy wrote:Good technique John. Especially the point about enlarging the canvas before
starting. I use DxO Optics to do this same sort of thing. It has custom made profiles for various lenses so unlike PSCS it should theoretcially give a better result. But it doesn't have a module for the Tokina lens you have

Peter, I tried to check on the DxO site, but it appears to be down at the moment... Please correct me if I'm wrong, but I think that DxO only corrects barrel and pincushion distortion and not vertical perspective distortion.
In fact, the flaw in my method above is that I didn't correct for pincushion distortion before adjusting the perspective...

While looking for info on DxO, I also came across and bought the ptLens plug-in for Photoshop. It seems to do most of what DxO does in this department with favourable reviews and at only US$5 it's a bargain... It does have calibrations for the Tokina 12-24, so I'm happy... It also does a better job of correcting CA than Photoshop, so I'm doubly happy

Interestingly, correcting for distortion in Portrait Orientation is a completely different ball-game...

I started off with this image:


and ended up with this one which I think looks more natural


I used a similar technique as above, but this time used ptLens to correct for pincushion distortion first and then used Lens Correction to correct the vertical Perspective. Due to the angle from which I took the shot, this was quite extr3me* and the vertical perspective slider needed to be pushed to the right-hand extremity*...

This time I didn't stretch the image horizontally, but maybe it needs a little bit...

* words changed to defeat the stupid word censor

wendellt wrote:I normally use the distort transform tool in photoshop

As with most things in Photoshop, there are more than one way to solve the problem.
I tend to use the Lens Correction filter because it has everything on one screen: Straightening, vignette correction, CA correction, barrel, pincushion, vertical and horizontal distortion - it also has a built in grid that gives you multiple reference points when correcting the distortion.

I agree that Edit-Transform has its moments, but I prefer to use Lens Correction. BTW... Does anyone know why Edit-->Transform is quite often greyed out and unavailable??? I haven't yet figured out what I need to do to be able to access that function...

leek wrote:

stubbsy wrote:Good technique John. Especially the point about enlarging the canvas before
starting. I use DxO Optics to do this same sort of thing. It has custom made profiles for various lenses so unlike PSCS it should theoretcially give a better result. But it doesn't have a module for the Tokina lens you have

Peter, I tried to check on the DxO site, but it appears to be down at the moment... Please correct me if I'm wrong, but I think that DxO only corrects barrel and pincushion distortion and not vertical perspective distortion.
In fact, the flaw in my method above is that I didn't correct for pincushion distortion before adjusting the perspective...

While looking for info on DxO, I also came across and bought the ptLens plug-in for Photoshop. It seems to do most of what DxO does in this department with favourable reviews and at only US$5 it's a bargain... It does have calibrations for the Tokina 12-24, so I'm happy... It also does a better job of correcting CA than Photoshop, so I'm doubly happy

John

DxO corrects barrel, pincushion and geometric distortion, chromatic aberration and vignetting (discussion here). Note that "Keystone correction, often loosely described as perspective correction, is not currently supported". It also corrects lens/camera softness and noise and offers a lighting engine to adjust things like shadows & highlights. Its big strength is the way it does each of these uses a module which is customised for the known attributes of a given lens and camera. It's biggest weakness is that same thing. If it doesn't have a module for your lens it only allows you to use the lighting module.

I've found it exceptionally useful with my 10.5 fiesheye for example. It is certainly not a replacement for Photoshop and in fact supports DNG output. I now routinely correct my 10.5 DX and 12-24 DX pics using DxO before doing anything else and I can see a difference. This isn't really as noticeable with the 24-120 and 70-200 VR lenses.

leek wrote:BTW... Does anyone know why Edit-->Transform is quite often greyed out and unavailable??? I haven't yet figured out what I need to do to be able to access that function...

My experience is it's greyed out when you haven't selected the image first.

stubbsy wrote:

leek wrote:BTW... Does anyone know why Edit-->Transform is quite often greyed out and unavailable??? I haven't yet figured out what I need to do to be able to access that function...

My experience is it's greyed out when you haven't selected the image first.

Aha... I knew it would be something simple Thanks Peter - another mystery solved...

Leek, it is greyed out when you are working on the background layer. Either double click background to make it 'layer 0' or drag background onto the new layer icon to duplicate it and work on that.

If your working on the whole layer, you don't need to select the area first, just make sure the layer is highlighted and visible.

CC