parallax adjustment after the fact

[4play]

thru digital manipulation. possible ? will it affect quality of print if so? i prefer the movements of a 4x5, but that is a ways off for me.

[PacAce]

4play wrote:
thru digital manipulation. possible ? will it affect quality of print if so? i prefer the movements of a 4x5, but that is a ways off for me.

I have no idea what you're talking about.

[4play]

parallax = convergence. i have always used the 2 synonymously (sp. ?). have i developed a bad habit ? is parallax not the proper term so people know what i mean ?

but... shoot a tall building from ground level & lines of sight "converge" to one central point.

the movements of the focal planes (front & rear standards) on a 4x5 will correct this. shoot a building from ground level & you can eliminate the parallax, or convergence, of its lines so what you get is a building w/ straight, parallel lines. NOT a lean-away-from-you-pyramid-imposter.

i know i can rotate an image thru software but am not aware if i can correct for parallax, virtually "tilting" the focal plane to obtain parallel lines when desired.

[mebow]

If you will read PS7 regarding perspective cropping you will find that any minor flaw caused by location of the camera vs the top of a building may be corrected with some minor limitations.

Mike

[john_houghton]

Parallax has nothing whatever to do with convergence or perspective distortion. It refers to the apparent change in position of a nearby object in relation to a more distant background when viewed from slightly different positions. We two eyed monsters are able to make use of this effect to perceive depth by comparing the slightly different views seen by our eyes. Cyclops, having only one eye, would have had to wave his head from side to side to get the same effect.

John

[stopbath]

I have used GIMP to correct convergance, and tilted imaged. I use the 'corrective' radio button and then line up grid to the convergance of the building (or tilt on the building if it's just a horizon that's tilted.) The program then calculates the correction needed.

It would be nice to have a Perspective Control Sensor. This is doable, since we no longer are using roll film. Naturally, camera body cost would be huge. But it would be nice.... Or perhaps a 1 X 1.25 (an ultra small 4 x 5) :)

[stoneylonesome]

Paint shop Pro 8 does a little of what your are asking, I've never used it so I cannot say how well it works

http://www.jasc.com/products/paintshoppro/photo.asp?

Manipulate images from digital cameras and scanners
Fix distorted perspective in photos easily with the Perspective Correction tool. Straighten a tilted or crooked photo without any guesswork using the Straighten tool. Browse, sort, rotate, and rename image thumbnails in a single window. Crop, Resize, and Rotate images. View EXIF information transferred from your camera.

http://www.jasc.com/

[PhotoAZ]

The answer with Photoshop is in the Transform menu BUT there are a few things you will need to do first.

Open Image (well dud!)
Ctrl R to bring up the Rulers on the side of the image
Take the mouse and move it into the rulers and left click hold down. Drag out and you will have a guild line come out. Place this guild line on the outer corner of the building. Do the same for the other side. Now you have two straight lines on either side of the image as a reference.
Select the whole image or press Ctrl A
Now Ctrl T to make it a Transform.
Go to Edit/Transform/Skew

You may need to make the area around the image a little bigger so that you can grab the corners a little easier. Just start moving the grab corners to adjust the image. Each point can be moved by themselves just like in a view camera except now you can grab just one corner and really pull it out. The guild lines will help you in your perspective and to make sure you don't go too far.

[4play]

thanks all for your replys.

evidently my syntax has been incorrect in equating parallax w/ convergence...

oh well, i was bound to make one mistake in my life sooner or later... ;)

[Yance]

Yeah, it's more "perspective correction". It depends on how much correction is needed. As you stretch the image there will be interpolation of the stretched areas. It isn't too apparent unless the correction is major. Don't expect too much but it can corect minor distortion.

[john_houghton]

Panorama Tools can be used to correct perspective distortion. It maps images onto a spherical surface such that the view from the centre of the sphere replicates the view from the camera position exactly. By outputting a rectilinear projection using this model, a geometrically accurate correction is achieved. There is no tugging of handles involved to make it "look right".

I did a quick correction and only partially cropped the result:

http://homepage.ntlworld.com/j.houghton/icech.jpg

John