DPChallenge: A Digital Photography Contest You are not logged in. (log in or register) 
 

DPChallenge Forums >> Current Challenge >> Correcting lens barrel distortion in Basic
Pages:  
Showing posts 1 - 24 of 24, (reverse)
AuthorThread
 02/22/2011 12:58:07 PM · #1
Yes, I have read the Basic rules. The pertinent part for me today is: "You may not distort or stretch your image in any way." I understand this. Here's the stupid question: Can I repair lens barrel distortion? I would love to use PTLens on an image to correct for lens barrel distortion. It appears to be prohibited, because it would take a corrective distortion to correct the distortion. Any possibility this would be allowed in Basic?
 02/22/2011 01:22:12 PM · #2
I think you will probably find that if you ask the SC, the answer you will most likely receive is that it is not legal. There was some discussion of this when I was on SC, and as I recall the team consensus is that it is not legal. I personally think it should be legal, but that's just me.
 02/22/2011 01:24:04 PM · #3
I would think that you cannot correct barrel distortion in basic, as that would be distorting the image you captured.

Tim
 02/22/2011 01:27:57 PM · #4
I believe it is illegal in Basic, and legal in Advanced.

ETA: In Advanced, the rules say "you may...use software to correct perspective, lens defects, or minor misalignments."

Message edited by author 2011-02-22 13:28:46.
 02/22/2011 01:39:25 PM · #5
Originally posted by jeger:
I believe it is illegal in Basic, and legal in Advanced.

This is correct.
 02/22/2011 01:39:27 PM · #6
Thanks for the replies. Much appreciated!
 02/22/2011 01:39:46 PM · #7
It's definitely not legal in basic, although I, also, think it should be. But we've had this discussion before, and SC has firmly stated it cannot be done. Seems to me it's just another way of penalizing the folks that can't afford premium optics, but what do I know? :-)

(Above is a satirical statement, people.)

R.
 02/22/2011 01:42:40 PM · #8
Originally posted by Bear_Music:
It's definitely not legal in basic, although I, also, think it should be. But we've had this discussion before, and SC has firmly stated it cannot be done. Seems to me it's just another way of penalizing the folks that can't afford premium optics, but what do I know? :-)

(Above is a satirical statement, people.)

R.

And good satire, it was!
 02/22/2011 02:10:33 PM · #9
i would love it to be in basic, but then if you are removing distortion, like cloning you aren't basic editing any longer.
 02/22/2011 02:13:20 PM · #10
Originally posted by mike_311:
i would love it to be in basic, but then if you are removing distortion, like cloning you aren't basic editing any longer.


I'd argue that point. I'd argue that the ability to correct optical distortions ought to BE a basic skill, but...

R.
 02/22/2011 02:34:30 PM · #11
Originally posted by Bear_Music:
Originally posted by mike_311:
i would love it to be in basic, but then if you are removing distortion, like cloning you aren't basic editing any longer.


I'd argue that point. I'd argue that the ability to correct optical distortions ought to BE a basic skill, but...

R.


basic skill, yes, basic editing, no.

even if its easy to remove distortion (its a checkbox in lightroom) doesn't mean that it should be allowed. fundamentally you are altering the image and completely change what your camera captured.

basic editing seems to allow you to push the colors and lightness of the pixels, not their position.

Message edited by author 2011-02-22 14:35:08.
 02/22/2011 02:38:23 PM · #12
Originally posted by mike_311:
Originally posted by Bear_Music:
Originally posted by mike_311:
i would love it to be in basic, but then if you are removing distortion, like cloning you aren't basic editing any longer.


I'd argue that point. I'd argue that the ability to correct optical distortions ought to BE a basic skill, but...

R.


basic skill, yes, basic editing, no.

even if its easy to remove distortion (its a checkbox in lightroom) doesn't mean that it should be allowed. fundamentally you are altering the image and completely change what your camera captured.

basic editing seems to allow you to push the colors and lightness of the pixels, not their position.


Except that they modified that to allow the cloning of sensor dust, which affects pixels and is a flaw-correcting operation. I'd submit that correcting for barrel distortion falls int he same category.

R.
 02/22/2011 02:47:31 PM · #13
Originally posted by Bear_Music:
Except that they modified that to allow the cloning of sensor dust, which affects pixels and is a flaw-correcting operation. I'd submit that correcting for barrel distortion falls int he same category.

R.

The distortion is a characteristic of the lens, the "bad pixels" are a characteristic of the dust particle. With the minimal cloning allowed you are changing the color of the obscured pixels to restore them to their original state had the optical path been clean, but correcting the distortion displaces pixels from their captured position and effects a change in the image.
 02/22/2011 02:48:18 PM · #14
maybe they figured that you cant tell if you have sensor dust and or hot pixels until you look at your images up close, when its too late.

lens distortion is something you are, or should be, aware of.
 02/22/2011 03:46:11 PM · #15
Originally posted by mike_311:
maybe they figured that you cant tell if you have sensor dust and or hot pixels until you look at your images up close, when its too late.

lens distortion is something you are, or should be, aware of.


Shhh... You're talking as if "they" can't hear you!!! They're here...
 02/22/2011 03:55:06 PM · #16
Originally posted by mike_311:
maybe they figured that you cant tell if you have sensor dust and or hot pixels until you look at your images up close, when its too late.

lens distortion is something you are, or should be, aware of.

Sure, but why should I be "punished" if I can only afford entry-level lenses that are rife with barrel distortion?
 02/22/2011 04:02:40 PM · #17
Originally posted by gcoulson:
Originally posted by mike_311:
maybe they figured that you cant tell if you have sensor dust and or hot pixels until you look at your images up close, when its too late.

lens distortion is something you are, or should be, aware of.

Sure, but why should I be "punished" if I can only afford entry-level lenses that are rife with barrel distortion?

Get further away from your subject and crop more then :)

Message edited by author 2011-02-22 16:02:51.
 02/22/2011 04:03:00 PM · #18
hey im right there with you, i own quite a few cheap lenses, i would love to see it in basic, but i can see why its not allowed.
 02/22/2011 04:03:34 PM · #19
Some of us can't afford cameras at all for which we have a choice of lenses ... and why should I be "punished" because I can't afford a camera that can shoot a usable picture at ISO 400 ...? Everyone's camera/system and post-processing capability will have some limitation or another, but we all get to play by the same rules.
 02/22/2011 04:07:58 PM · #20
Originally posted by gcoulson:
Originally posted by mike_311:
maybe they figured that you cant tell if you have sensor dust and or hot pixels until you look at your images up close, when its too late.

lens distortion is something you are, or should be, aware of.

Sure, but why should I be "punished" if I can only afford entry-level lenses that are rife with barrel distortion?


Because you should be punished peasant, be away with you and bring me my pipe and Remy Martin before I whip you.
 02/22/2011 04:18:29 PM · #21
Originally posted by wingyisleeds:
Originally posted by gcoulson:
Originally posted by mike_311:
maybe they figured that you cant tell if you have sensor dust and or hot pixels until you look at your images up close, when its too late.

lens distortion is something you are, or should be, aware of.

Sure, but why should I be "punished" if I can only afford entry-level lenses that are rife with barrel distortion?


Because you should be punished peasant, be away with you and bring me my pipe and Remy Martin before I whip you.

Would you like a 70-200/2.8L with your pipe, master?
 02/22/2011 04:34:17 PM · #22
Premise: The rules should attempt not to favor high-end equipment, as far as possible
Premise: The rules should be internally consistent

While the above are not written anywhere, I believe they are common sense. Furthermore, let me state that while I recognize that the capabilities of a P&S are much different than a DSLR (Paul gives a good example with ISO) they are not necessarily inherently inferior. In fact, if my goal is to achieve large DoF, they are superior.
All that aside, I believe that the current ruling prohibiting correcting lens distortion in Basic is not in keeping with the above. Specifically:
- the rule favors high-end glass; P&S cameras, and consumer lenses, particularly zooms, tend to have significantly higher distortion than higher-end glass. I can still shoot very viable submissions with my old Nikon 995, but I dare not try to shoot a building interior at wide angle. Looks awful. Easily correctable in post, but not legal in basic.
- The rule is inconsistent with other rulings on correction. Correction of CA is, AFAIK, allowed. Not only is this the correction of a defect in the lens as opposed to in/on the sensor (one differentiator that is cited in support of the current ruling) but it also moves pixels, however slightly. It is, in fact, per-channel distortion correction.

Question: Why would we choose to *not* allow this type of correction?
- If allowing it would make the ruleset much more difficult to enforce
- If allowing it violates the spirit of Basic Editing
I submit that allowing correction of lens distortion does not violate the spirit of the Basic Rules, in that corrective measures have been broadly allowed, and lens distortion correction is so universally applied that many applications are natively capable of dealing with it for most major camera/lens combinations. I also submit that, if properly implemented, it does not make the Basic Rules any harder to enforce. It's dead easy to figure out whether any change in the image reduces or increases distortion. The one special case is "correction" of fisheye "distortion." In fact, the "fish question" is a red herring (sorry, had to)! Fisheye lenses are fisheye lenses, not rectilinear lenses. Making a fisheye image into a rectilinear image is not correction.
 02/22/2011 04:35:06 PM · #23
Originally posted by gcoulson:
Originally posted by wingyisleeds:
Originally posted by gcoulson:
Originally posted by mike_311:
maybe they figured that you cant tell if you have sensor dust and or hot pixels until you look at your images up close, when its too late.

lens distortion is something you are, or should be, aware of.

Sure, but why should I be "punished" if I can only afford entry-level lenses that are rife with barrel distortion?


Because you should be punished peasant, be away with you and bring me my pipe and Remy Martin before I whip you.

Would you like a 70-200/2.8L with your pipe, master?


haha :)
 02/22/2011 04:44:03 PM · #24
Originally posted by kirbic:
Premise: The rules should attempt not to favor high-end equipment, as far as possible
Premise: The rules should be internally consistent

While the above are not written anywhere, I believe they are common sense. Furthermore, let me state that while I recognize that the capabilities of a P&S are much different than a DSLR (Paul gives a good example with ISO) they are not necessarily inherently inferior. In fact, if my goal is to achieve large DoF, they are superior.
All that aside, I believe that the current ruling prohibiting correcting lens distortion in Basic is not in keeping with the above. Specifically:
- the rule favors high-end glass; P&S cameras, and consumer lenses, particularly zooms, tend to have significantly higher distortion than higher-end glass. I can still shoot very viable submissions with my old Nikon 995, but I dare not try to shoot a building interior at wide angle. Looks awful. Easily correctable in post, but not legal in basic.
- The rule is inconsistent with other rulings on correction. Correction of CA is, AFAIK, allowed. Not only is this the correction of a defect in the lens as opposed to in/on the sensor (one differentiator that is cited in support of the current ruling) but it also moves pixels, however slightly. It is, in fact, per-channel distortion correction.

Question: Why would we choose to *not* allow this type of correction?

- If allowing it would make the ruleset much more difficult to enforce
- If allowing it violates the spirit of Basic Editing
I submit that allowing correction of lens distortion does not violate the spirit of the Basic Rules, in that corrective measures have been broadly allowed, and lens distortion correction is so universally applied that many applications are natively capable of dealing with it for most major camera/lens combinations. I also submit that, if properly implemented, it does not make the Basic Rules any harder to enforce. It's dead easy to figure out whether any change in the image reduces or increases distortion. The one special case is "correction" of fisheye "distortion." In fact, the "fish question" is a red herring (sorry, had to)! Fisheye lenses are fisheye lenses, not rectilinear lenses. Making a fisheye image into a rectilinear image is not correction.


hard to argue with this logic.

Message edited by author 2011-02-22 16:44:23.
Pages:  
Current Server Time: 08/07/2025 04:13:47 PM

Please log in or register to post to the forums.


Home - Challenges - Community - League - Photos - Cameras - Lenses - Learn - Help - Terms of Use - Privacy - Top ^
DPChallenge, and website content and design, Copyright © 2001-2025 Challenging Technologies, LLC.
All digital photo copyrights belong to the photographers and may not be used without permission.
Current Server Time: 08/07/2025 04:13:47 PM EDT.