how to correct panorama distortion created by UWA + parallax error?

Try using "Smartblend" to blend the images.

http://wiki.panotools.​org/SmartBlend

The image you posted is pretty small - to what specific parallax issues are you referring?

kirk

kirkt wrote in post #16742424
Try using "Smartblend" to blend the images.

http://wiki.panotools.​org/SmartBlend

The image you posted is pretty small - to what specific parallax issues are you referring?

kirk

using smartblend gives similar results.

notice in the image that the room should be linear (completely straight) instead of converging 'V' shaped lines.

the parallax issue is with regards to the lens/nodal point itself.

The only way that you could photograph that room without introducing the curved effect is to set the camera up on a long rail and take the pano by sliding the camera along the rail parallel to the wall behind you. Otherwise you will always be dealing with the problem that the far side ends of the room are always much further away than the center of the room directly in front of you. Getting further away from the "straight" line you are trying to photograph the less apparent distortion you will get, as the differences in distance are much reduced. This is why you tend to not notice this with landscape images, far fewer straight lines, and they are usually much further away. Even so anywhere where you have a wide pano and straight lines this becomes an issue.

For example in this just over 360 degree example I was positioned on a mound that ran parrallel to the right hand dirt track in the center of the image. That track then makes a 90 degree left turn next to the gate, and then runs away again. Even though the track takes a left turn almost right in front of me the fact that the turn is so much closer than the two parts of the track running away from me still ends up giving the effect of the tracks actually bending to the right. The only real way to correct this would be to print it out and mount it on a curved (concave) backing so that all of the components regain the correct appearance. With a 360 pano you would mount it in a circle and stand in the center

IMAGE LINK: http://www.flickr.com …s/alan-evans/11720107494/

Oh - your issue is not parallax, it is the spherical projection of your image. You can use the adaptive wide angle tool in PS CC to straighten the curved lines that should be straight.

kirk

BigAl007 wrote in post #16742989
The only way that you could photograph that room without introducing the curved effect is to set the camera up on a long rail and take the pano by sliding the camera along the rail parallel to the wall behind you. Otherwise you will always be dealing with the problem that the far side ends of the room are always much further away than the center of the room directly in front of you. Getting further away from the "straight" line you are trying to photograph the less apparent distortion you will get, as the differences in distance are much reduced. This is why you tend to not notice this with landscape images, far fewer straight lines, and they are usually much further away. Even so anywhere where you have a wide pano and straight lines this becomes an issue.

For example in this just over 360 degree example I was positioned on a mound that ran parrallel to the right hand dirt track in the center of the image. That track then makes a 90 degree left turn next to the gate, and then runs away again. Even though the track takes a left turn almost right in front of me the fact that the turn is so much closer than the two parts of the track running away from me still ends up giving the effect of the tracks actually bending to the right. The only real way to correct this would be to print it out and mount it on a curved (concave) backing so that all of the components regain the correct appearance. With a 360 pano you would mount it in a circle and stand in the center

IMAGE LINK: http://www.flickr.com …s/alan-evans/11720107494/
Stickledown Panorama by alan-evans, on Flickr

I suppose that you could try a similar effect in PS, but the problem is that you would need to map the image on to the inside of a sphere of the correct radius and then crop a rectangle from it. This would either need a very high resolution image (at least near the final Z axis) or lots of enlargement of the image at large distances from the Z axis. Not to mention finding just the right radius of sphere to do the projection with.

Alan

yup, though that would be logistically tough to get the rail lined up properly throughout the length of the room.

i tried using that tool in PS CC but it seems to have no effect on straightening at all (tried all the available options @ dropdown).

^^ You have to actually lay down lines in the preview window and specify them to be straight - you can force them to be vertical or horizontal, too. The menu options give you control over what type of correction you are performing - if you assembled your pano in PS, then select Panorama (it should automatically be selected).

Google Adaptive Wide Angle filter in PS and watch a tutorial.

kirk

BigAl007 wrote in post #16742989
The only way that you could photograph that room without introducing the curved effect is to set the camera up on a long rail and take the pano by sliding the camera along the rail parallel to the wall behind you. Otherwise you will always be dealing with the problem that the far side ends of the room are always much further away than the center of the room directly in front of you. Getting further away from the "straight" line you are trying to photograph the less apparent distortion you will get, as the differences in distance are much reduced. This is why you tend to not notice this with landscape images, far fewer straight lines, and they are usually much further away. Even so anywhere where you have a wide pano and straight lines this becomes an issue.

I've done this method before, and it's not very "clean" either. Each individual image will have some perspective, and when you stitch them all together they don't line up. All those converging rows of chairs are going to make a huge mess.

Unless you slide along the whole length of the room, and take 30,000 1-pixel-wide images along the length of the slider...

nathancarter wrote in post #16748333
I've done this method before, and it's not very "clean" either. Each individual image will have some perspective, and when you stitch them all together they don't line up. All those converging rows of chairs are going to make a huge mess.

Unless you slide along the whole length of the room, and take 30,000 1-pixel-wide images along the length of the slider...

Yes - I have done this approach for architectural shots of building fronts on a town street. You have to take a pretty sizable number of images and it will work, as long as there is not a lot of depth portrayed away from the plane with most of the detail. Then you have to be judicious in your masking in of the detail that does recede or protrude.

It sounds like the OP was maybe unaware that the curved lines effect is "normal" for such spherical panoramic images.

kirk

Interesting thread, I've tried to do a "straight" panorama of a street of houses before and failed abysmally due not being able to fix the perspective changes between each shot.

I pretty much figured I needed to used a longer lens and get as far away as possible. I wasn't quite thinking 30,000 1 pixel wide images though! BTW wouldn't that technique essentially be the slit scan effect used in 2001:A Space Oddessy and at the finishing post of a horse race?

Yep, the slit-scan effect is what I was thinking, but with a moving camera instead of moving subjects. For all practical purposes, it's impossible. Maybe if you poured thousands of dollars into specialized equipment, and dozens (hundreds?) of hours into developing a technique or process.

... and I think the end result would still be unsettling and not believable. NO perspective at all, is gonna be a little weird... like those old "folk art" paintings with the hilariously wrong perspective on people and houses and barns.

[edit] Actually - there's a thread around here somewhere, a guy developed software to read individual images from a movie file, and create a slit-scan effect. So you might be able to accomplish it by putting the camera on a really long slider, and taking a movie as you slide it along the rail. It'd take a little bit of math and experimentation to figure out the right combination of movie framerate and slider speed, but maybe it's do-able.

Watch this video by Serge Ramelli. He describes the Photoshop CC process very well. http://www.youtube.com …wQ&feature=em-uploademail

Nathan the hardware required is not really that difficult to build, could probably do it for around a couple of hundred bucks/quid. you have two options, shoot video and move the camera relatively quickly, or shoot JPEG and move the camera much more slowly. I think RAW would be out as the frame rate possible but the buffer will fill. There are plenty of cameras now though that will shoot continuous JPEGs at a decent rate without filling the buffer. For absolute accuracy you would want to do a step/shoot/step process. The big question then would be your "step" rate and also if you could get away with using more than a single column of pixels, if so how many?. This would actually be like having a giant camera with a very large focal plane shutter.

Alan

nathancarter wrote in post #16752964
Yep, the slit-scan effect is what I was thinking, but with a moving camera instead of moving subjects. For all practical purposes, it's impossible. Maybe if you poured thousands of dollars into specialized equipment, and dozens (hundreds?) of hours into developing a technique or process.

I have seen some inexpensive digital slit cameras.

They basically function the same as a normal scanner. Nothing too strange with the lens - it's just that the camera sensor isn't a square but a line and you move the camera at a constant speed while recording a "video" from that one-pixel wide sensor.

BigAl007 wrote in post #16753728
Nathan the hardware required is not really that difficult to build, could probably do it for around a couple of hundred bucks/quid. you have two options, shoot video and move the camera relatively quickly, or shoot JPEG and move the camera much more slowly. I think RAW would be out as the frame rate possible but the buffer will fill. There are plenty of cameras now though that will shoot continuous JPEGs at a decent rate without filling the buffer. For absolute accuracy you would want to do a step/shoot/step process. The big question then would be your "step" rate and also if you could get away with using more than a single column of pixels, if so how many?. This would actually be like having a giant camera with a very large focal plane shutter.

Alan

A camera with video function and support for emitting raw video can be used without producing huge data volumes - the receiving end of the raw video can throw away most of the video data since all that is needed is a narrow band. If using a single pixel column, then the movement of the camera needs to match the expected horisontal resolution. In the end, it will be very hard to move the camera at so exact speed that the image gets square pixels - better to move too slowly and then rescale horisontally.