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Nick Temple-Fry
19th September 2009, 12:18 AM
The walls are usually OK and I'm pretty good on windows. But there is no doubt about it, my floors tend to sag.

Now I know what the problem is - I tend to stand in the corner like johnny no-friends - and everything I see has an odd angle to it. But I like it there, the view is more interesting.

OK I know that lens design assumes a vanishing point at the centre of the scene, and if I shoot the scene from the rhs that the actual vanishing point for lines going into the scene moves to the rhs as a direct function of my position.

Now the GIMP will draw me a square grid and let me wobble things quite happily. So that takes care of perspective from a 'flat' point of view. But I want to define a grid based along those lines that go into the image, geometric convention says those lines should meet at a vanishing point. So then I just have to wobble the image to bring those 'depth' lines to converge on a single point.

Is there a tool that lets me do this - maybe I'm missing something on The GIMP.

Perhaps I just don't understand.

But it has been bugging me for quite a while..............HELP!!!

snaarman
19th September 2009, 07:59 AM
Oooh dear. I wish I understood the question properly.. However PTlens and (perhaps) PS Elements offer Lens distortion adjustment. This can include both vertical and horizontal perspective.. So you can correct or tweak converging verticals, but you can also tweak converging horizontals..

However, I don't know if any of those tools would assist, given you are taking the picture from a corner...

If you have saggy floors caused by barrel/pincusion distortion in some way that doesn't also affect the verticals - then I don't quite know what to suggest.

Is it something you could correct under the enlarger?? :)

Pete

snaarman
19th September 2009, 08:35 AM
OK, so here is one of yours I tweaked in said manner.

However I don't think this is what you were after :-)

http://e-group.uk.net/gallery/data/622/nick_adjusted.jpg (http://e-group.uk.net/gallery/showphoto.php/photo/17926)

Pete

Nick Temple-Fry
19th September 2009, 11:32 AM
OK - and it maybe I'm starting from a misunderstanding.

But drawing perspective lines onto mine and Petes picture gives

http://e-group.uk.net/gallery/data/500/Nick_maladjusted_jpg.jpg (http://e-group.uk.net/gallery/showphoto.php/photo/17927)

Pete has brought those lines closer to a point (or at least a smaller locus) - but at the expense of picture size and introducing a 'bend' to the foreground alter rail - which suggests that part of the effect of the correction has been to force my POV closer to the centre.

Indeed that is what all perspective tools seem designed to do - they attempt to change the POV of the photographer back to what would be central to the photograph. The classic example would be this poor shot

http://e-group.uk.net/gallery/data/500/Nick_persp_example.jpg (http://e-group.uk.net/gallery/showphoto.php/photo/17928)

where wobbling the sides has lifted the photographers POV 5 feet into the air.

But I don't want to change my POV - I just what my perspective lines to meet neatly and the rest of the picture to follow.

(I can envisage the maths - it would be a function of the lengths of the converging perspective lines and the distance between them, preceded by a trial and error determination within the locus formed by the crossing lines to determine the vanishing point. Almost certainly simpler than the maths used to move the POV of the camera to match the centre of the lens).

Maybe it's out there somewhere - maybe there's a good book.

(Oh and I do use PTLens - but I do find its perspective function less easy than The GIMP).

Nick

Ellie
25th September 2009, 09:39 PM
Nick, have you tried using ShiftN?

It's freeware that has a few tricks up its' sleeve if you've got time to fiddle around with it. The automatic correction is quite good on its' own. http://www.shiftn.de/

Nick Temple-Fry
25th September 2009, 11:14 PM
Nick, have you tried using ShiftN?

It's freeware that has a few tricks up its' sleeve if you've got time to fiddle around with it. The automatic correction is quite good on its' own. http://www.shiftn.de/

Ah - that's a new one - I'll look it up.

Thanks Ellie

Nick

Zuiko
25th September 2009, 11:50 PM
Sadly, Nick, unless you can find dedicated software which will actually do what you require, I think the only solution would be a large format technical camera with which you could correct the distortions in camera using the independant film back and lens board movements. It would still be a b*gg*r to get exactly right (sorry, didn't mean to scare the horses ;)), but it could be done.

I suspect you would not wish to go down that route so unfortunately you'll have to rely upon finding better software, or waiting until it becomes available. Take consolation in the knowledge that most of us find your images pretty damn amazing and don't notice the minor flaws (excuse the pun) that you, as a perfectionist, clearly agonise over.

Nick Temple-Fry
26th September 2009, 12:03 AM
Sadly, Nick, unless you can find dedicated software which will actually do what you require, I think the only solution would be a large format technical camera with which you could correct the distortions in camera using the independant film back and lens board movements. It would still be a b*gg*r to get exactly right (sorry, didn't mean to scare the horses ;)), but it could be done.

I suspect you would not wish to go down that route so unfortunately you'll have to rely upon finding better software, or waiting until it becomes available. Take consolation in the knowledge that most of us find your images pretty damn amazing and don't notice the minor flaws (excuse the pun) that you, as a perfectionist, clearly agonise over.

At the end of the day 3 dimensions into 2 don't go. But I'm still learning so hope for advice as to a better compromise.

But I see the flaws, that's the problem.

Nick

Zuiko
26th September 2009, 12:07 AM
At the end of the day 3 dimensions into 2 don't go. But I'm still learning so hope for advice as to a better compromise.

But I see the flaws, that's the problem.

Nick

Good luck, I appreciate what you are trying to do. Are there any forums dedicated to this type of thing where you could get more specialist advice than we can offer?

johnwb
27th September 2009, 08:10 AM
If I understand your situation correctly, may I suggest that a program called Serif Photplus 9 had a 'warp' tool within it, and a 'pinch and punch' tool. The former tool had the ability to pull pixels in a given direction, and the latter the ability to apply a concave or convex spherical distortion to the image and apply these effects to a selection or a layer. This may starighten out the rail.

Regards JohnWB

Nick Temple-Fry
27th September 2009, 10:57 AM
If I understand your situation correctly, may I suggest that a program called Serif Photplus 9 had a 'warp' tool within it, and a 'pinch and punch' tool. The former tool had the ability to pull pixels in a given direction, and the latter the ability to apply a concave or convex spherical distortion to the image and apply these effects to a selection or a layer. This may starighten out the rail.

Regards JohnWB

Ahh - but my rail was straight before Pete got his hands on it.

PTLens corrects lens distortion and the GIMP has both warp and perspective tools - it is as much about how programs display perspective. In art (when you are about 12 and would rather blow things up in chemistry) you are taught to visualise/represent perspective by drawing lines along features that have depth - these should meet at the vanishing point. All perspective tools I can find just allow you to place a grid across the front (fine for 'flat' presentations only), at the moment I only have very manual/non-dynamic work-arounds.

Thanks

Nick

snaarman
3rd October 2009, 07:45 AM
Ahh - but my rail was straight before Pete got his hands on it.

PTLens corrects lens distortion and the GIMP has both warp and perspective tools - it is as much about how programs display perspective. In art (when you are about 12 and would rather blow things up in chemistry) you are taught to visualise/represent perspective by drawing lines along features that have depth - these should meet at the vanishing point. All perspective tools I can find just allow you to place a grid across the front (fine for 'flat' presentations only), at the moment I only have very manual/non-dynamic work-arounds.

Thanks

Nick

Yes, sorry about the bent rail! PTlens can do lens distortion and perspective/rotate etc all at the same time. I use it to straighten horizons and remove residual barrel and pincusion, and the results are generally nice if used with restraint. It may be I let it apply distortion correction when it wasn't needed :-)

Pete