Lens distortion correction is a resolution killer

[forpetessake]

Have you noticed that enabling distortion correction in camera significantly affects image resolution? Interestingly it happens not only in the corners where distortions are the worst, but even the center resolution suffers noticeably.

 

[Keit ll]

What are you more likely to notice in an image , obvious distortion or a marginal loss of centre resolution ?

 

[blue_skies]

Have you noticed that enabling distortion correction in camera significantly affects image resolution? Interestingly it happens not only in the corners where distortions are the worst, but even the center resolution suffers noticeably.

I take distortion corrections if it means a cheaper/faster/more usable/more compact lens design...

Also, see below, which is the better image to you? Distortion corrections are very useful - not everyone has a T&S lens. Consider de-fishing techniques as well...

(note - corrections were applied using DxO, not in-camera corrections)

(disclaimer - I should have taken more care about the center 'blow-up' - e.g. people look distorted in center).


OOF 12mm (E16+UWA) uncorrected


12mm (E16+UWA) distortion corrected


16mm (E16) distortion corrected



--
Cheers,
Henry

 

[Dunnlang]

I am going to have to vote for the first image. It may be partially due to the people at the center though.

I like that the columns appear to soar upward, but do not curve much, if at all. It gives a good sense of scale to the interior.

 

[KennyXL]

Have you noticed that enabling distortion correction in camera significantly affects image resolution? Interestingly it happens not only in the corners where distortions are the worst, but even the center resolution suffers noticeably.

I take distortion corrections if it means a cheaper/faster/more usable/more compact lens design...

Also, see below, which is the better image to you? Distortion corrections are very useful - not everyone has a T&S lens. Consider de-fishing techniques as well...

(note - corrections were applied using DxO, not in-camera corrections)

(disclaimer - I should have taken more care about the center 'blow-up' - e.g. people look distorted in center).


OOF 12mm (E16+UWA) uncorrected


12mm (E16+UWA) distortion corrected


16mm (E16) distortion corrected

--
Cheers,
Henry

Everybody in your distortion-corrected photos look like they gained 50 pounds.

 

[Digital Nigel]

Yes, I don't like the converging verticals distortion correction, either. If done at all, I think only a very subtle change should be done, so that there is still some converging verticals -- making the verticals completely parallel is actually a distortion in its own right. I have DxO, but this is a feature I rarely use, and then only sparingly.

 

[chromnd]

I think you're talking about a perspective correction using 3rd party tools, but for my understanding the topic is the in-camera distortion correction.

 

[proxy]

Gallery view is not good enough to show what you're talking about re. resolution especially that you post pics in diff. resolutions. Can you post some crops to show that?

Beside that... correction you are showing is a total failure, doing the opposite of what it should be doing. Only the first pic has the right proportions (people).

 

[DUSTY LENS]

Gallery view is not good enough to show what you're talking about re. resolution especially that you post pics in diff. resolutions. Can you post some crops to show that?

Beside that... correction you are showing is a total failure, doing the opposite of what it should be doing. Only the first pic has the right proportions (people).

I disagree , in the first pic it is far to much distortion because it makes me feel like the walls and the steel beams are going to cave in on people below , and me too .

Fact is human vision never does this when they are standing in person and looking at the scene .

There will be the same effect as looking at rail road tracks on the ground but human vision does not see this as distortion either . Maybe because it is on the ground .

I like the straight parallel vertical walls and steel beams . it looks far more natural to me .

This is also the most used application of the shift lenses and of the vertical shift in view cameras .

It can be used to keep vertical lines parallel and it does this without the use of any distortion and without and distortion software if the lens is very low in distortion this makes the most beautiful and sharp images .

When you walk through tall buildings your eyes do not see curved vertical walls or beams , they all appear parallel and straight . This is as they are in fact . So when ones vision is confronted with vertical structures it does not make them appear curved or even slanted .

What I am saying is that you can replace the real in person scene with a perfectly parallel verticals image and your vision will treat it the same as the in person view . nothing gets distorted or curved in either case . It is more natural to your vision .

Dusty

 

[forpetessake]

Have you noticed that enabling distortion correction in camera significantly affects image resolution? Interestingly it happens not only in the corners where distortions are the worst, but even the center resolution suffers noticeably.

I take distortion corrections if it means a cheaper/faster/more usable/more compact lens design...

You can't make those cheap lenses nowhere as good as those optically corrected. I've looked at midrange zooms, and even 18-55, which doesn't have severe distortions to begin with, suffer noticeable sharpness deterioration everywhere in the frame after camera applies geometric correction.

Also, see below, which is the better image to you? Distortion corrections are very useful - not everyone has a T&S lens. Consider de-fishing techniques as well...

Though it doesn't have anything to do with this discussion, the first image looks better, because all corrected images are unnaturally distorted.

(note - corrections were applied using DxO, not in-camera corrections)

(disclaimer - I should have taken more care about the center 'blow-up' - e.g. people look distorted in center).


OOF 12mm (E16+UWA) uncorrected


12mm (E16+UWA) distortion corrected


16mm (E16) distortion corrected

--
Cheers,
Henry

 

[viking79]

Have you noticed that enabling distortion correction in camera significantly affects image resolution? Interestingly it happens not only in the corners where distortions are the worst, but even the center resolution suffers noticeably.

Optical distortion correction can hurt resolution as well.

I notice no difference in the center with barrel distortion correction. Something else is happening if it is (or you are correcting pincushion). It likely hurts the midway performance as well.

Here is an example of a Fuji lens, 16-50mm f/3.5-5.6, at 16mm it has a correction for around 8% barrel distortion (according to Photozone). Lightroom automatically corrects the RAWs from this camera so I don't ever see the distorted RAW image. This characteristic is common of distortion corrected lenses.

In the optically corrected Fuji 14mm f/2.8 lens, the corners and midway points are a bit higher, but it is hard to say how much softness is from distortion correction, and how much is from cruddy lenses. As I said, the below chart is very typical MTF50 for software corrected lenses, sharp centers but edges drop off a bit. In this case the lens is still plenty good at the edges.

This picture is from my blog:

Fuji XC 16-50mm f/3.5-5.6

Here is the optically corrected Sony 16mm f/2.8, this was a good copy.

Sony SEL 16mm f/2.8

 

[blue_skies]

Have you noticed that enabling distortion correction in camera significantly affects image resolution? Interestingly it happens not only in the corners where distortions are the worst, but even the center resolution suffers noticeably.

I take distortion corrections if it means a cheaper/faster/more usable/more compact lens design...

You can't make those cheap lenses nowhere as good as those optically corrected. I've looked at midrange zooms, and even 18-55, which doesn't have severe distortions to begin with, suffer noticeable sharpness deterioration everywhere in the frame after camera applies geometric correction.

There are two types of users (or more, I just think of two distinct types): those that seek perfection and those that seek to have fun.

My point merely was that, once you accept that 'good-enough' is 'good-enough', you have a lot more flexibility - in-camera corrections, JPG shooting, post-edit flows. Using a 'compromised' or 'flawed' lens design, but getting images that come out of it might satisfy those that seek to have fun. I think the typical consumer, using the camera for fun/hobby/non-commercial uses.

The effort to make non-compromised APS-C lenses leads to $1k lenses, and even those suffer from artifacts, especially wide open. If we accept FW corrections, we may have a line of $400 lenses. (e.g. compare E20 and E24Z). For the brand, I would welcome that. Cameras nowadays do have powerful processing engines and can do what previously was impossible or required specific work-flows. What is wrong with this? P&S cameras are doing it for years...

Now, if you want to use the system professionally, or commercially, and your only choice is a FW-compromised lens, than the trade-off can be negative. I do agree with you here. For these purposes, high IQ lenses should be available.

Perhaps future FE lenses can fill this purposes? At least for some FLs, these could be uncompromised designs?

Also, see below, which is the better image to you? Distortion corrections are very useful - not everyone has a T&S lens. Consider de-fishing techniques as well...

Though it doesn't have anything to do with this discussion, the first image looks better, because all corrected images are unnaturally distorted.

I know, I just wanted to illustrate that we sometimes do a lot to the image in post, not for IQ, but for other reasons - HDR, corrections, crop/highlight, vignetting, softening, portrait, sharpening, etc. Lens FW correction would then be just one factor. My images illustrate this to some extent. I have seen some great de-fishing applications too, not for maximum IQ, but for fun or dramatic effects...

 

[proxy]

Gallery view is not good enough to show what you're talking about re. resolution especially that you post pics in diff. resolutions. Can you post some crops to show that?

Beside that... correction you are showing is a total failure, doing the opposite of what it should be doing. Only the first pic has the right proportions (people).

I disagree , in the first pic it is far to much distortion because it makes me feel like the walls and the steel beams are going to cave in on people below , and me too .

Fact is human vision never does this when they are standing in person and looking at the scene .

...

Dusty

You disagree with what specifically? I'm afraid you misunderstood.

First picture is uncorrected, I assume straight from camera showing natural lens distortion in relation to focus length. You disagree with that? This is a fact of life, laws of optics in action. Your eye is not the lens and your lens is not the eye, they both see differently. What your eye sees is processed and corrected in your brain, without your knowledge. Cameras do the same but only on demand (or you can do that in PP).

OP spoke about the resolution degradation, I'm not discussing perspective correction. Just mentioned it. Failure I'm talking about is most likely due to UWA which camera cannot know of or account for. That is why correction looks hilarious - people are shortened.

Again, I'd like to see crops illustrating how correction degrades the resolution. Problem is pics are taken with UWA attached to the lens and because of that camera is unable to apply the correct pattern to straighten the picture. It has to be done in PP. In addition pics are posted in different resolutions.

 

[Keit ll]

Most gross distortion corrected images need to be stretched to restore normal proportions. The photo shown above needs about 23% increase in height to look reasonably normal , which is a lot but the photo was grossly distorted to begin with.

Some people are more accepting of some types of distortion than others , I personally don't like any distortion if it can be avoided & nearly always apply perspective correction to my photos. It's true that some marginal loss of resolution can occur but you have to be aware of this technical aspect of PP & have to look hard to find it , in normal prints of reasonable size you would be very hard pressed to see it.

 

[Digital Nigel]

Surely "correcting" perspective is actually to add distortion? The converging verticals aren't an error -- they're what the camera actually saw. We're all perfectly used to seeing images like that all the time, as most professional images and videos don't deliberately distort pictures by changing the verticals in an artificial way. When you artificially distort the image to make the verticals parallel, you're creating an impossible image, as the camera's position is too low.

 

[Franka T.L.]

and that's pretty much why I try my best to refrain from those so call wonderful lens ( that literally relying on soft correction ).

 

[proxy]

... on the other hand there is no way to avoid them. Perspective correction can be done right and wrong way. One has to evaluate the content of the image itself to arrive at proper approach. Even then the result is not guaranteed, may take several tries. But to blame lenses for that is a misunderstanding.

 

[DUSTY LENS]

Gallery view is not good enough to show what you're talking about re. resolution especially that you post pics in diff. resolutions. Can you post some crops to show that?

Beside that... correction you are showing is a total failure, doing the opposite of what it should be doing. Only the first pic has the right proportions (people).

I disagree , in the first pic it is far to much distortion because it makes me feel like the walls and the steel beams are going to cave in on people below , and me too .

Fact is human vision never does this when they are standing in person and looking at the scene .

...

Dusty

You disagree with what specifically? I'm afraid you misunderstood.

First picture is uncorrected, I assume straight from camera showing natural lens distortion in relation to focus length. You disagree with that? This is a fact of life, laws of optics in action. Your eye is not the lens and your lens is not the eye, they both see differently. What your eye sees is processed and corrected in your brain, without your knowledge. Cameras do the same but only on demand (or you can do that in PP).

OP spoke about the resolution degradation, I'm not discussing perspective correction. Just mentioned it. Failure I'm talking about is most likely due to UWA which camera cannot know of or account for. That is why correction looks hilarious - people are shortened.

Again, I'd like to see crops illustrating how correction degrades the resolution. Problem is pics are taken with UWA attached to the lens and because of that camera is unable to apply the correct pattern to straighten the picture. It has to be done in PP. In addition pics are posted in different resolutions.

I do not mean to be disagreeable , It just comes naturable in my case .

You stated " ( Only the first pic has the right proportions (people). ) "

As far as I can see Most of what you say above is correct or at least not disputed by me .

But this one " ( Only the first pic has the right proportions (people). ) " is what I disagree with specifically .

As you correctly ( in My Opinion ) stated : Your eye is not the lens and your lens is not the eye, they both see differently. What your eye sees is processed and corrected in your brain, without your knowledge. And I must add to that that your eye can correct a photograph that has already had the vertical lines corrected back to true vertical lines as they were in the original scene before the Lens / Camera made them slanted in at the top .

But again you say " I assume straight from camera showing natural lens distortion in relation to focus length. You disagree with that? "

No and No , this is not what I disagree with , and no , this is not lens distortion , natural or not natural .

Also , You support what I agree with in this " ( Your eye is not the lens and your lens is not the eye, they both see differently. What your eye sees is processed and corrected in your brain, without your knowledge. Cameras do the same but only on demand (or you can do that in PP).) But this also disputes what you said here " ( I'm not discussing perspective correction. ) " . becauses you are talking about " ( I'm talking about is most likely due to UWA ) " .

This is what happens to straight lines which are not photographed with their off axis lines held perpendicular to the lens axis . This is what happened in the top photograph , The off axis lines are not held parallel to the sensor focus plane and this is not lens distortion either . It is the perspective effect of near and far objects in the scene being recorded with differing sizes , ( reproduction ratios ) .

Dusty

 

[DUSTY LENS]

Surely "correcting" perspective is actually to add distortion? The converging verticals aren't an error -- they're what the camera actually saw. We're all perfectly used to seeing images like that all the time, as most professional images and videos don't deliberately distort pictures by changing the verticals in an artificial way. When you artificially distort the image to make the verticals parallel, you're creating an impossible image, as the camera's position is too low.

Actually the act of straightening converging vertical or horizontal lines is not distoition , nor is it creating impossible images .

It happens all of the time , and it is not distortion or impossible in the case of a shift lens and in view cameras using shift control .

But it also happens with unshifted photos simply by holding the lens angle so that the vertical lines are parallel to the image plane or the sensor / film plane .

It is a normal part of optics and photography . the Human eye is perfectly able to apply distortions to images which are recorded with parallel lines which are reproduced parallel as in the real physical world .

A case in reality could be a block ( or other material ) 6 foot high wall which is straight on the top and a constant 6 feet high from one end to the end which is miles away . The camera can be positioned so that the plane of the wall is parallel to the plane of the side of the wall which is facing the camera . It will be reproduced with the top and the bottom of the wall having parallel and straight lines on the film or on the sensor .

This is a common occurrence in document copy photographs . It is certainly not distortion .

Dusty

 

[Digital Nigel]

Surely "correcting" perspective is actually to add distortion? The converging verticals aren't an error -- they're what the camera actually saw. We're all perfectly used to seeing images like that all the time, as most professional images and videos don't deliberately distort pictures by changing the verticals in an artificial way. When you artificially distort the image to make the verticals parallel, you're creating an impossible image, as the camera's position is too low.

Actually the act of straightening converging vertical or horizontal lines is not distoition , nor is it creating impossible images .

It happens all of the time , and it is not distortion or impossible in the case of a shift lens and in view cameras using shift control .

But it also happens with unshifted photos simply by holding the lens angle so that the vertical lines are parallel to the image plane or the sensor / film plane .

It is a normal part of optics and photography . the Human eye is perfectly able to apply distortions to images which are recorded with parallel lines which are reproduced parallel as in the real physical world .

A case in reality could be a block ( or other material ) 6 foot high wall which is straight on the top and a constant 6 feet high from one end to the end which is miles away . The camera can be positioned so that the plane of the wall is parallel to the plane of the side of the wall which is facing the camera . It will be reproduced with the top and the bottom of the wall having parallel and straight lines on the film or on the sensor .

This is a common occurrence in document copy photographs . It is certainly not distortion .

Dusty

It's fine if the rectangular object is at infinity or indeed if it's a simple flat object (like, say, a notice on a wall). I do correct the image to make such signs rectangular, and crop the rest of the image. But if it's of, say, a very high room, where the camera is obviously only a meter or two off the floor (as can be seen from people in the image), then to make the back wall rectangular introduces the impossible viewpoint. To look real, the camera should be placed half the height of the ceiling.

But, in any case, this discussion of stretching converging verticals to be parallel is really a separate discussion from the subject of this thread, which was about whether correcting lens distortion affected image resolution. Clearly, converging verticals in wide angle shots is not a distortion in the lens -- lens is accurately recording what it sees. Some people like to artificially alter the shot in post-processing to make to appear as they think the brain would transform the same scene if viewed directly; others (probably the majority), prefer not to add this distortion, and let the brain do its usual transformational work, as it would with any video or movie and the vast majority of published still images.