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perspective correction: a discussion (1 pic, 3 versions)

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Dez, I also get a slight sense of a miniature model of the tower grafted into the scene in your version. More than that though, I get an illusion of the the tower leaning to the left. I think both impressions are partly caused by a correction that goes past a natural human perception of the scene perspective. There would be some convergence.

But that leaning to the left effect on the tower is also enhanced by the fact that the vertical lines on the buildings in the distance, which fall along the vertical centerline of the image at about camera eye level where we would expect the least visual distortion, are now distinctly leaning to the left.

Also righting the tower completely with the perspective tool has resulted in a distortion of it's form so that the local perspective view of it's horizontal structural elements is now at odds with the camera eye viewpoint. This would also contribute to the model impression.

It's a complex problem, and one I'm glad to see discussed here.

--
Roscoe

 
Being an old-hand from the times when the most you could do was some dodge and burning in the lab, I'm amazed by how much the digital lab and other tech stuff allows in terms of new possibilities.

TS lenses are very expensive and I'm not an architecture photog, all my shooting is done, with some few exception, in the spur of the moment and handheld, so likely such a lens would be left collecting dust somewhere.

In fact, I'm thinking about getting a wider zoom, not yet decided on which one (the one I want is the new 14-24 f/2.8, which would give, for my style, the perfect range of 21-36mm, but it's likely overkill on a D80, but...).
--
Regards, Renato.
http://www.flickr.com/photos/11435304@N04
OnExposure member
http://www.onexposure.net/

You cannot depend on your eyes when your imagination is out of focus
(Mark Twain)
 
Thomas, I have exactly same sense when I look at this image by Dez.

BTW, above (one of the posts in this thread) it's mentioned the importance of the point in image to be seen as the "center". In such a small version, it gets a bit lost, but on a larger print or monitor, seen from an appropriate distance, it'd be more reasonable to feel the center point which would result from the convergence of lines (point at infinity in a perspective analysis).

We're, essentially, discussing what the great Italian masters did 550 years ago when they introduced perspective as a tool for 2D representation of 3Dl space.

It's a nice subject in art and science, and I recommend the book

The Science of Art: Optical Themes in Western Art from Brunelleschi to Seurat (Paperback)
by Martin Kemp (Author)

which has a very good introduction to perspective and projective geometry as related to art.
troscoe said:
Dez, I also get a slight sense of a miniature model of the tower
grafted into the scene in your version. More than that though, I get
an illusion of the the tower leaning to the left. I think both
impressions are partly caused by a correction that goes past a
natural human perception of the scene perspective. There would be
some convergence.

But that leaning to the left effect on the tower is also enhanced by
the fact that the vertical lines on the buildings in the distance,
which fall along the vertical centerline of the image at about camera
eye level where we would expect the least visual distortion, are now
distinctly leaning to the left.

Also righting the tower completely with the perspective tool has
resulted in a distortion of it's form so that the local perspective
view of it's horizontal structural elements is now at odds with the
camera eye viewpoint. This would also contribute to the model
impression.

It's a complex problem, and one I'm glad to see discussed here.

--
Roscoe

Click to expand...
--
Regards, Renato.
http://www.flickr.com/photos/11435304@N04
OnExposure member
http://www.onexposure.net/

You cannot depend on your eyes when your imagination is out of focus
(Mark Twain)
 
binary_eye wrote:
snip
binary_eye said:
If the tower is the main focus of the photo, then the
perspective should be corrected. However, if the scene as a whole is
the focus of the photo, then the perspective should not be corrected.
In this latter case, it allows any viewer to see the scene closer to
what it appeared in reality, given they view the center of the photo
as their center of view.
Click to expand...
I had this notion(or one very similar) in my head as well. Some of the distorted elements in a photo might add to the impact of the image. The Leaning Tower of Eiffel didn't bother me at all in this pic. It may have been the most significant element in the photo but I think it also played a supporting role. IMO it needed to look tall and imposing... that bit of lean helped it do that. ONce you staighten it out, it loses something.

--
http://leelaycock.blogspot.com
http://www.flickr.com/photos/k-bien/

'No point in steering now.' -- Doug McKenzie
 
rhlpetrus said:
you look good an professional in this pic. I bet you had the D300 on
a tripod on a self-timer or remote, didn't you?
Click to expand...
Thank you sir :D

Actually, this was taken with my co-worker's point & shoot while in a wooded area in Staten Island.
--
Dez

http://photos.dezmix.com
 
LOL! He actually works for DPR!! :)
C'mon... you gotta know he's an admin. hahaha...
jkjond said:
Member said:
I am a professional Land
Surveyor. We deal with straight lines, angles, distances and numbers
all day. Buildings are supposed to be plumb (90 degrees vertical to
the ground) If all buildings "leaned" in real life, we'd all be in
trouble........and would get ALOT of work :P
Click to expand...
You know as well as I do that you aren't a professional land surveyor
at all.

You are a full time, and I mean 24/7, dpr addict with a hobbiest's
interest in surveying.
Click to expand...
--



http://leungphotography.smugmug.com
 
I'm not an architect but I do work as a project manager for an architectural firm. I hope that counts for something.... ;-)

I don't quite get the reasoning that leaning buildings are ok, natural or whatever. They are not. Apart from the tower of Pisa buildings do not lean over. And that is also not the way we see buildings in real life. I really doubt that we see converging lines in the corners of our eyes. Apart from the fact that they become the centre of our attention the moment we start taking notice, our brain simply knows what is supposed to be vertical. It's just like the built-in automatic white balance we all have. Just as we don't see blueish of reddish pieces of white paper we don't see converging lines. Our brain simply corrects that.

Besides that, we don't look at our world with just one 'centre' and we don't look at images like that either. On the contrary, pictures invite our eyes to wander around and a good composition usually leads our eyes across a picture.

BUT... perspective correction in photography is often a trade-off. There are simply technical limitations that make it often impossible to get everything right. That's a major difference between paintings and photographs: in a painting it IS possible to get everything right. If we could do that with photography I guess we wouldn't have disccussions like this and we would agree that real verticals are the most natural. Or do we really have a problem with all those 'real' verticals in almost every painting?

--
My gallery: http://www.flickr.com/photos/klaastuin/
 
Sorry I miissed this thread earlier in the week Renato but I haven't had much time in front of a computer over the last few days.

Perspective in architectural drawing is something that you can spend years studying as they can be constructed mathematically from the plan of a building for any given viewpoint....these days for work it's all done with dedicated software drawing packages like Autocad.

The problem you have here is that your image is a photo and not a mathematically constructed drawing so you are dealing with very strong lens distortion which can be impossible to fully correct even with specialist software, especially when, as here, you place an object with the height and curved sides of the Eiffel Tower in the edge of the frame where distortion is greatest.

In my (limited) photographic experience, with any wide angle lens shot like this, lens perspective distortion increases in strength as you approach the edges of the frame so although you will be able to correct the tower in photoshop so that it is no longer leaning (ie it is vertical through the center line) you will find that the curve of the two sides is still asymmetric with the one nearest the frame edge curving at a different rate from the inner one....this is a problem that I've come up against several times myself and I haven't been able to correct it.

As for my opinion on the issue of your photo, I strongly prefer the corrected version. Although it's clear that there are still perspective distortions, the worst bits have now been fixed....as others have said: it no longer looks like the Leaning Tower of Pisa.

I don't own a tilt-shift lens so can't comment on their use but with wide angle photography using my 10-20 lens I usually try to keep the camera horizontal if there are buildings in the shot and then I will crop in post-processing. Keeping the camera horizontal like this goes a long way toward minimising vertical perspective distortion but for shots like yours of very tall objects like the Eiffel Tower it can be difficult to get far enough back from the subject.

One trick that can work in cities or inside buildings to minimise wide angle lens distortion is to try to get to a vantage point which is about half way up in height when compared to the building you are photographing....this way you can keep your lens horizontal as half the subject is below and half is above the center line.

The photo below is about as extreme as it gets in terms of trying to control perspective distrortion in an architectural photo. It is of a victorian shopping arcade in Southport that my company helped restore. This shot would have been impossible from ground floor level but by using a first floor balcony as a vantage point I didn't need to correct anything in photoshop....you can still see obvious wide angle lens distortion but at least the verticals are straight.

In situations where there is no option but to tilt the camera up to get everything in then I'll either try to leave plenty of room for post processing distrotion correction & cropping or else I'll try and exaggerate the distortion so that it becomes part of the photo....the lighthouse photo that I used at the start of the challenge is an example of this.

Ian
http://ianbramham.aminus3.com/
http://photo.net/photos/ian.bramham



 
ianbramham said:
Sorry I miissed this thread earlier in the week Renato but I haven't
had much time in front of a computer over the last few days.
Click to expand...
I had missed your reply, thanks for taking time to do it.
ianbramham said:
Perspective in architectural drawing is something that you can spend
years studying as they can be constructed mathematically from the
plan of a building for any given viewpoint....these days for work
it's all done with dedicated software drawing packages like Autocad.

The problem you have here is that your image is a photo and not a
mathematically constructed drawing so you are dealing with very
strong lens distortion which can be impossible to fully correct even
with specialist software, especially when, as here, you place an
object with the height and curved sides of the Eiffel Tower in the
edge of the frame where distortion is greatest.
Click to expand...
The lens distortion I pretty much got right (3rd in original post here), suing the lens distortion tool in CNX, so that it may be leaning, but not bended, at least.
ianbramham said:
In my (limited) photographic experience, with any wide angle lens
shot like this, lens perspective distortion increases in strength as
you approach the edges of the frame so although you will be able to
correct the tower in photoshop so that it is no longer leaning (ie it
is vertical through the center line) you will find that the curve of
the two sides is still asymmetric with the one nearest the frame edge
curving at a different rate from the inner one....this is a problem
that I've come up against several times myself and I haven't been
able to correct it.
Click to expand...
Indeed, very tough and probably almost impossible to corect without an absolutely free pixel motion tool, which I doubt exists.
ianbramham said:
As for my opinion on the issue of your photo, I strongly prefer the
corrected version. Although it's clear that there are still
perspective distortions, the worst bits have now been fixed....as
others have said: it no longer looks like the Leaning Tower of Pisa.
Click to expand...
Interesting, opinions seem to split on this one, but I take your opinion a bit higher than most others', given your activity and interest in formal aspects of composition. You agree with both Alex and Dez, so, good compacny there. But John, who's a free-thinker regarding our metier, seems to think rules are for the masses ;)
ianbramham said:
I don't own a tilt-shift lens so can't comment on their use but with
wide angle photography using my 10-20 lens I usually try to keep the
camera horizontal if there are buildings in the shot and then I will
crop in post-processing. Keeping the camera horizontal like this goes
a long way toward minimising vertical perspective distortion but for
shots like yours of very tall objects like the Eiffel Tower it can be
difficult to get far enough back from the subject.
Click to expand...
Good advice, since I'm likely getting a WA zoom in NY in a couple of weeks, should be more careful with that, your suggestion makes good sense geometrically.
ianbramham said:
One trick that can work in cities or inside buildings to minimise
wide angle lens distortion is to try to get to a vantage point which
is about half way up in height when compared to the building you are
photographing....this way you can keep your lens horizontal as half
the subject is below and half is above the center line.

The photo below is about as extreme as it gets in terms of trying to
control perspective distrortion in an architectural photo. It is of a
victorian shopping arcade in Southport that my company helped
restore. This shot would have been impossible from ground floor level
but by using a first floor balcony as a vantage point I didn't need
to correct anything in photoshop....you can still see obvious wide
angle lens distortion but at least the verticals are straight.
Click to expand...
Very nice shot, one cans see a lot of distortion in the people walking below, but building actually looks real.

Thanks for your reply again, very helpful.
ianbramham said:
In situations where there is no option but to tilt the camera up to
get everything in then I'll either try to leave plenty of room for
post processing distrotion correction & cropping or else I'll try and
exaggerate the distortion so that it becomes part of the photo....the
lighthouse photo that I used at the start of the challenge is an
example of this.

Ian
http://ianbramham.aminus3.com/
http://photo.net/photos/ian.bramham



Click to expand...
--
Regards, Renato.
http://www.flickr.com/photos/11435304@N04
OnExposure member
http://www.onexposure.net/

You cannot depend on your eyes when your imagination is out of focus
(Mark Twain)
 
Klay said:
Klay said:
If the tower is the main focus of the photo, then the
perspective should be corrected. However, if the scene as a whole is
the focus of the photo, then the perspective should not be corrected.
In this latter case, it allows any viewer to see the scene closer to
what it appeared in reality, given they view the center of the photo
as their center of view.
Click to expand...
I had this notion(or one very similar) in my head as well. Some of
the distorted elements in a photo might add to the impact of the
image. The Leaning Tower of Eiffel didn't bother me at all in this
pic. It may have been the most significant element in the photo but
I think it also played a supporting role. IMO it needed to look tall
and imposing... that bit of lean helped it do that. ONce you
staighten it out, it loses something.
Click to expand...
My view as well, but if you read on people are pretty much split on this one.

--
Regards, Renato.
http://www.flickr.com/photos/11435304@N04
OnExposure member
http://www.onexposure.net/

You cannot depend on your eyes when your imagination is out of focus
(Mark Twain)
 
MotorCityJim said:
--
Jim K...just outside Detroit, MI
DeeEighty; DeeFifty; CeeTwentyOneHundred; EffZeeFiveK

http://www.pbase.com/jkorsog ...Pbase supporter
http://motorcityjim.fotopic.net/
http://www.flickr.com/photos/motor_city_jim/
Click to expand...
you're both in good company here, Alex, Dez and Ian.

Thanks for participating.
--
Regards, Renato.
http://www.flickr.com/photos/11435304@N04
OnExposure member
http://www.onexposure.net/

You cannot depend on your eyes when your imagination is out of focus
(Mark Twain)
 
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