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3D Crosstalk (Ghosting) versus Fusion Problems (1 Viewer)

Mike Ballew

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I've been a stereo photography enthusiast for 32 years now. I'm also a huge 3-D movie buff, and have made an effort to see as many classic and recent 3-D films as possible.

I talk a lot about this eccentric hobby of mine. It's gotten to the point where my friends, who have at best only a casual interest in the subject, sometimes think to mention things like interocular, interaxial, parallax, convergence and crosstalk in ordinary conversation.

Once I went with a friend to see an IMAX science documentary. The imagery was pretty spectacular, with plenty of negative parallax and objects projecting into theatre space. A few minutes into the show, my friend leaned over and whispered, "Say, is this that 'crosstalk' you're always talking about?"

I didn't know what to say. I wasn't seeing any crosstalk. Like, none. "What do you mean?" I asked.

"Sometimes the picture looks doubled, even with the glasses. Isn’t that crosstalk?"

Immediately I reasoned that my friend was having trouble fusing the images, and was conflating that with crosstalk.

That little incident nags at me to this day, and makes me wonder: Is it possible that some folks—not all, just a few—who complain about crosstalk or ghosting, especially in older 3-D films, are actually having problems with fusion and stereopsis?

Of course, the best way to determine this is to advise people to check for crosstalk in one eye at a time. If you see a double image through one or the other lens of the 3-D glasses, then that's genuine crosstalk. But the question still stands. Your thoughts?
 

Wayne_j

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IMAX 3D can show ghosting if your head is tilted while viewing. Straightening the head should fix the issue.
 

Mike Ballew

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You are absolutely correct, linear polarizers can show ghosting if one's head is tilted, something I've been aware of for more than 30 years. Perhaps I should have mentioned that the presentation we were watching that day did not employ polarizers, but liquid crystal glasses. But, as I say, there was no ghosting or crosstalk in evidence in the presentation we were watching. None.

We even traded headsets. I had no problems, while my friend still perceived a "doubling" of the image, though he became less vocal about it as the film progressed.

In my view, my friend's difficulty was probably owing to an undiagnosed vision problem of some sort. But it wasn't something he was comfortable discussing in any detail afterwards, so we let the subject drop.

I just wonder how often people blame fusion problems on ghosting or crosstalk in their display, quite innocently, without knowing any better.
 

Mark-P

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I've often wondered that myself: if a lot of the "ghosting" issues people have with 3D is just a failure to converge their eyes.
 

StephenDH

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I used to be able to view 3D photos through a stereoscope with no problems even though I wear glasses. Switching to varifocals made this impossible unless I removed my specs.
I've never had a problem with 3D movies though.
 

Stephen_J_H

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I ran into some problems with fusion earlier this year, as well as some weird changes to my short range vision. Turned out that I had type 2 diabetes, which is now under control with medication and diet, and my vision is back to what it once was. Sounds like your friend may need to see his optometrist at the very least.
 

Mike Ballew

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StephenDH, I had another friend who declined to even look through a stereoscope, so sure was she that her poor vision would impede her enjoyment.

Stephen_J_H, I'm happy to hear that your health and vision have taken a turn for the better.

I've read several times that Julian Gunzburg, of 1950s Natural Vision fame, believed that 3-D movies could help expose undiagnosed vision problems. He also believed in their potential as a therapeutic exercise to improve most anyone's vision.

I can tell you that when I was a kid, I had lazy eye in my left eye. Our family ophthalmologist was at a loss for a time how to handle the problem; I think surgery was even considered. Serendipitously, independent of his influence, I discovered 3-D movies, printed anaglyphs, and stereo photography. Within a year, my vision in my left eye was much improved and my eyes were working much better as a pair. Purely anecdotal, I know, but I’d like to think that 3-D movies, properly made and presented, could be of great benefit to people beyond their simple entertainment value.
 

David_B_K

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David M. Ballew said:
I've read several times that Julian Gunzburg, of 1950s Natural Vision fame, believed that 3-D movies could help expose undiagnosed vision problems. He also believed in their potential as a therapeutic exercise to improve most anyone's vision.

I can tell you that when I was a kid, I had lazy eye in my left eye. Our family ophthalmologist was at a loss for a time how to handle the problem; I think surgery was even considered. Serendipitously, independent of his influence, I discovered 3-D movies, printed anaglyphs, and stereo photography. Within a year, my vision in my left eye was much improved and my eyes were working much better as a pair. Purely anecdotal, I know, but I’d like to think that 3-D movies, properly made and presented, could be of great benefit to people beyond their simple entertainment value.
David, your story makes sense to me. One reason I am not really into 3D anymore is that I have vision problems as well. Graves Eye disease has caused most of my problems. I have had 6 eye surgeries and cannot quite get my eyes to see a single image unless I wear glasses fitted with prisms to pull my eyes into alignment. Actually, the glasses do a pretty good job on distance viewing (which would encompass TV and movie viewing). For reading, I usually black out one lens.

However, the problem I have that is similar to yours is that I have glaucoma in my left eye. I can see out of the eye, but not terribly well. It does not bother me when I am using both eyes to look at something or one image. My brain seems to ignore the eye. If I looked at my screen with the bad eye, it would no longer look high def. But when both eyes are open, I only see high def. My brain somehow fools me into not noticing the poor vision from the left eye. If I open and close the bad eye, nothing really changes the way I see things, aside from a loss of peripheral vision on that side.

A lazy eye is very similar. Everyone has a dominant eye, and apparently, one's brain will simply ignore the "lazy eye". Sometimes people essentially become blind in the lazy eye because the brain has "turned it off". I have no doubt that your interest in stereo vision essentially forced that eye to get into shape and improved your sight in that eye.
 

StephenDH

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I remember reading many years ago about a woman (I think in Germany) who suffered from double vision for many years and was instantly able to see properly when she tried on a pair of Polaroid 3D specs.
 

StephenDH

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David_B_K said:
David, your story makes sense to me. One reason I am not really into 3D anymore is that I have vision problems as well. Graves Eye disease has caused most of my problems. I have had 6 eye surgeries and cannot quite get my eyes to see a single image unless I wear glasses fitted with prisms to pull my eyes into alignment. Actually, the glasses do a pretty good job on distance viewing (which would encompass TV and movie viewing). For reading, I usually black out one lens.

However, the problem I have that is similar to yours is that I have glaucoma in my left eye. I can see out of the eye, but not terribly well. It does not bother me when I am using both eyes to look at something or one image. My brain seems to ignore the eye. If I looked at my screen with the bad eye, it would no longer look high def. But when both eyes are open, I only see high def. My brain somehow fools me into not noticing the poor vision from the left eye. If I open and close the bad eye, nothing really changes the way I see things, aside from a loss of peripheral vision on that side.

A lazy eye is very similar. Everyone has a dominant eye, and apparently, one's brain will simply ignore the "lazy eye". Sometimes people essentially become blind in the lazy eye because the brain has "turned it off". I have no doubt that your interest in stereo vision essentially forced that eye to get into shape and improved your sight in that eye.
A doctor where I used to work told me that It's possible to see 3D using just one eye but I wouldn't recommend it for extended viewing. If you look at a 2D image (preferably moving) with just one eye and restrict your view (e.g. make a tunnel with your hand) so that no screen edges (or anything other than the image) are visible, then the image will become 3D as your brain responds to the depth cues as though it were looking at the real world.
It's a bit undignified but it works.
Proof that it's all in the mind.
It's always struck me that when the drinks tray appears to be halfway between the viewer and the screen in "The Bubble", it's halfway for everyone in the cinema, no matter where they are sitting.
 

Mike Ballew

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StephenDH said:
It's always struck me that when the drinks tray appears to be halfway between the viewer and the screen in "The Bubble", it's halfway for everyone in the cinema, no matter where they are sitting.
Stephen, that same fact has always fascinated me. When the amount of negative parallax on the screen equals the distance between a pair of human eyes, then the object popping off the screen appears to be halfway between the screen and the viewer. And this is true for all persons viewing the image, regardless where they are sitting, so long as they are not seated at some oblique angle with an imperfect view of the screen. (I say all this for the benefit of others who may not be as familiar with this phenomenon as we are.)

I seem to recall that one important proponent of 3-D cinema was a believer that negative parallax ought never have a value higher than the average human interocular. I wonder what this person would think today, when the sum total of onscreen parallax typically amounts to only one or two centimeters!
 

StephenDH

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David M. Ballew said:
Stephen, that same fact has always fascinated me. When the amount of negative parallax on the screen equals the distance between a pair of human eyes, then the object popping off the screen appears to be halfway between the screen and the viewer. And this is true for all persons viewing the image, regardless where they are sitting, so long as they are not seated at some oblique angle with an imperfect view of the screen. (I say all this for the benefit of others who may not be as familiar with this phenomenon as we are.)

I seem to recall that one important proponent of 3-D cinema was a believer that negative parallax ought never have a value higher than the average human interocular. I wonder what this person would think today, when the sum total of onscreen parallax typically amounts to only one or two centimeters!
More proof that it's all in the mind. :3dglasses:
I should add that almost everyone in the cinema (including me) attempted to grab the tray of drinks.
I hope that this scene works as well on 3DTV as it does in the cinema.
 

RolandL

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StephenDH said:
More proof that it's all in the mind. :3dglasses:
I should add that almost everyone in the cinema (including me) attempted to grab the tray of drinks.
I hope that this scene works as well on 3DTV as it does in the cinema.
Depends on how far you are away from your TV screen. For the maximum 3D effect you should be about 1.3 times the screen width.

In my family room I sit about about 2 times the width from the 55 inch TV. When an object like the cod fish comes out of the screen in the blu-ray IMAX Under The Sea, its a few feet between me and the TV.

In my home theatre I sit about 1.3 times from the 138 inch image. For the same scene, its inches from my face.
 

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