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04-22-2008, 10:39 AM   #1
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fixing perspective problems

With some regularity I take a photo in which there is some perspectival distortion. I don't actually photograph a lot of buildings, but a building photograph is the easiest example of the problem I'm thinking about. If you are close to the building when you shoot, the front of the building will look trapezoidal rather than rectangular or square. In other words, I start with a photo that looks a bit like a capital letter A and I need to turn it into a capital H:

A
H

What do people use to fix these problems? I do nearly all of my post-processing in Lightroom and Light Crafts LightZone, neither of which has tools for handling perspective distortion. I know that Photoshop can do it but I don't have Photoshop and don't plan to buy it, certainly not for this. I downloaded The Gimp a while back and used it to fix a photo that had this problem, and perhaps that's my best option, but this is the only thing I'd use The Gimp for. Does the Pentax software (which I do not have installed) have this feature? Are there third-party utilities available that do this? I can't find one. I have something called PTLens that was recommended by someone (someone, I think in this forum) but it doesn't actually do what I need. It lets me turn the photo one way or another, but not to fix this problem.

I may have asked this question in this forum before but I can't find my earlier thread. And I'm still searching for a solution that's better than using the Gimp. If I get no answers, well, I'll conclude there's not a better solution.

Thanks,

Will

04-22-2008, 10:44 AM   #2
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Hugin does perpective correction in addition to panorama stitching: hugin - Panorama photo stitcher

Specific tutorial: Hugin tutorial — Perspective correction
04-23-2008, 06:26 AM   #3
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I use Photoshop - filter - distort - lens correction and the sliders under transform: Vertical perspective and Horizontal perspective.

It is really simple to use and works well.
04-23-2008, 07:43 AM   #4
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QuoteOriginally posted by ukbluetooth Quote
I use Photoshop - filter - distort - lens correction and the sliders under transform: Vertical perspective and Horizontal perspective.
As I said in my original post: "I know that Photoshop can do it but I don't have Photoshop and don't plan to buy it, certainly not for this."

Will

04-23-2008, 10:52 AM   #5
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DxO?

DxO can do that and no, it doesn't only work for the lenses they have modules for.
It is for K10D , however.
You can downoad a free trail from the site.

DxO Labs - Home
04-23-2008, 11:01 AM   #6
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Will

I use PSP X2. It does have perspective correction, that I have found works very well. (it is almost like looking around corners.

All you need to do is insure you have some references that you know are parallel (both horizontal and vertical)

You simply take the correction box and place one corner on each corner of your rectangle, and click OK/

If you want, post a photo, and I will show you what it can do.
04-23-2008, 12:51 PM   #7
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Here's an example of perspective correction in PSPX2. On the left is the original PEF converted to JPG, and on the right is the image after processing. I really like the result...

Last edited by code4code5; 06-08-2008 at 11:16 PM.
04-23-2008, 01:40 PM   #8
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Thanks to everybody who has replied. Very helpful to know what different folks are using. I tried a couple of the suggestions and found a few more. hugin is rather complicated, and so are a couple of the other little programs that I've tried. I read the documentation on a couple different programs and never could figure out how to fix a photo. I'd prefer NOT to spend $$ on either PaintShop Pro or DxO, although I'm sure these are very capable.

So I downloaded and reinstalled The Gimp. Decided that it won't hurt to have it handy for the rare times when I really need it; and if I decide that the UI is just too retro for me (which I might), I'll pull Photoshop Elements off the shelf and reinstall it.

Thanks for the example shots from the hospital. Yes, this is exactly the sort of thing that I need to do myself from time to time.

Below are two shots showing what I can do with The Gimp. The Gimp doesn't give me as much control as I'd like. Notice that the front edge of the stage in the "fixed" version still isn't perfectly straight. On the plus side, however, doing this in the Gimp is as easy as pie and that's important. You basically get a transform tool with 4 corners and you just drag the corners until you fix things. I could probably straighten that bottom line out - but it might cost me the loss of a couple actors on both sides of the photo and I didn't want to pay that price.

One day, perhaps, either Lightroom or LightZone will provide this feature.

Will

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04-23-2008, 01:55 PM   #9
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do you lose resolution by doing this?
04-23-2008, 01:57 PM   #10
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will

looks interesting.

As I said I use PSP X2 (but it is my main image processing software)

It is similar in interface, you have a box with 4 corners that you allign to what you want as the correct points and click OK Interface is simple, and you can also streighten things out (i.e. level). I note you have a little barrel distortion in the shot, PSP X2 can fix that also
04-23-2008, 02:05 PM   #11
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QuoteOriginally posted by k100d Quote
do you lose resolution by doing this?
Not entirely sure what you mean by "resolution," but the basic simple answer to your question is, no. A high-res original has more pixels than are needed, and I suppose that helps. And the program doing the stretching must interpolate pixels as needed.

In the example that I posted, I didn't use a full-res original. I started with an exported photo that was 1000x500 (pixels). The fixed file is 967x490. The loss occurs because it's necessary to chop off some of the stuff on the sides. But other than that, the resolution (as in level of detail) remains pretty much the same.

Will
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