What is this 3D issue i see a lot...that NOBODY even mentions ?! - Page 3 - AVS Forum
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post #61 of 73 Old 04-15-2014, 06:02 PM
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Even with parallel camera films the "cameras don't follow" as you put it.  Yes, we focus on what's dead center in our eyes, but that also doesn't matter: Our eyes are free to reconverge regardless of whether or not the source is parallel or convergent.

I agree with this, so let me clarify. The problem is distortion. With converged cameras, there is vertical disparity introduced in the edges, which is problematic. It should be easy to see this in the images above. With the parallel camera 3D image, you can look and focus anywhere in the image and have no problem, no vertical disparity.

 

Sort of.  In real life it's much the same, and we're more than adept to it. Further, each eye will see information that the other eye cannot see at all.  These "disparities" are all easily handled by the brain.


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post #62 of 73 Old 04-15-2014, 07:38 PM
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These "disparities" are all easily handled by the brain.

Disparities that are due to the left/right offset of our eyes, of course. That's the basis for stereoscopic vision. Vertical disparity, no. Our eyes can fuse a small amount of vertical disparity, but it's not comfortable and it's not natural. The greater the camera toe-in, the greater the distortion in the edges and the more vertical disparity present when viewing those areas, and so the greater chance that some viewers will feel discomfort. The closer to parallel the cameras are, the less.

We might not be able to prove exactly what issue the OP is seeing, but I think varying amounts of toe-in is a plausible explanation (one of many) for why some movies are comfortable and others (IMAX documentaries) are not.
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post #63 of 73 Old 04-15-2014, 07:46 PM
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These "disparities" are all easily handled by the brain.

Disparities that are due to the left/right offset of our eyes, of course. That's the basis for stereoscopic vision. Vertical disparity, no. Our eyes can fuse a small amount of vertical disparity, but it's not comfortable and it's not natural.

 

I understood what you were saying: it's why I said "further".  Not "natural"?  You understand that this also happens when you look at something IRL, right?

 

By the way, even with parallel cameras, what's preventing this effect?  The right camera will still receive a taller image from items that are closer to it (the right side of the box), and vice versa, parallel or not.


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post #64 of 73 Old 04-15-2014, 08:21 PM
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I think we're talking about different things. I should say vertical parallax. It's a known disadvantage of shooting with converged cameras and a direct result of keystone distortion.

What we don't know how much toe-in there was shooting a particular scene in a particular film, and how much keystone distortion was or wasn't corrected in post production. Does anyone?
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post #65 of 73 Old 04-15-2014, 09:17 PM
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Originally Posted by Airion View Post

I think we're talking about different things. I should say vertical parallax. It's a known disadvantage of shooting with converged cameras and a direct result of keystone distortion.

 

No we're talking about the same thing, I was just incorrect about this. Image Distortions in Stereoscopic Video Systems


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post #66 of 73 Old 04-17-2014, 11:06 AM
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I believe I have a good understanding of parallel vs converged cameras, but I admit that this information (how exactly movies were shot) is not readily available. Please share it if you have it!
It was just a matter of observing what I was seeing. I was also missing some understanding myself (see below). See, Beowulf not only rendered with parallel cameras, but it left them parallel for the presentation. It's easy enough to spot if you take the glasses off for a second, especially in an outdoor scene. The mountains off in the distance have no separation. With converged cameras, the objects in the far distance will be highly separated to give them the appearance of being very far away. The advantage of this rendering method is that you've got more room to play with separation in the negative space, and can result in a presentation that displays more depth (so to speak, technically it's all pop-out) between background and foreground objects. That's one reason I think people consider Beowulf to be a very good 3D presentation, and I agree.

The part of the equation I was missing was the idea of altering the footage in post, and changing the point of convergence using footage captured by two parallel cameras, resulting in the look of something shot with converged cameras. So in that respect, my statement about converged cameras being the standard may be incorrect... the presentation is converged, in that there's a specific "center point" of the scene that's at screen depth, and there's both additional depth behind, and pop-out in front. It turns out that doesn't necessarily have squat to do with how it was filmed on-set.

My hands-on experience with 3D is via CGI rendering. My app, LightWave, has stereoscopy built into it, and I can use something that's in between parallel and converged cameras... cameras that are technically converged, but the program removes the keystoning and renders "flat" as if they were parallel, but with the fixed convergence point already determined in the software prior to rendering. The result is a cleaner render, and a more acceptable and natural-feeling 3D effect. I honestly didn't know how such a thing could be done using actual cameras, but now that I read here a bit more, the solution seems obvious.. just fiddle with it in post.

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post #67 of 73 Old 04-17-2014, 11:37 AM
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interesting....my guess is that 90% of people that watch 3D encounter the big issues we are speaking about since the Opening of this topic....but people assume that these problems ARE part of the 3D, hence many people not liking watching movies and describing it as "head hurting"; unfortunately.....

tell me, if converged and parallel cameras are not ideal....and both have issues.....is there any new type of camera (hello james cameron!) that will be released that will offer perfect 3D ? or should manufacturers INVENT another type of screen to resolve the matter ?

Right now there is no perfect recording method to offer everyone the same level of comfort when viewing 3D. I was just pointing out, and this is just from what I've read, because it appeared like some were saying that the cause of uncomfortable 3D is because it was shot in either parallel or converged, which I do not believe is the case. When you read about both methods, both have advantages and both have disadvantages, but if there's discomfort because of a problem with parallax or keystoning it was likely not perfected in post, which both methods require.

I read something about another format war in this thread, which I think is getting out of hand a bit: parallel vs. converged. First these aren't really competing formats, are they? They're just different techniques, and perhaps even the same rig is capable of both methods. I don't know that, just saying.

To get 3D perfect for everyone? That's decades away. I can imagine it would involve a convex sensor, similar to our eyes for recording. The 3D would need to be adjusted to the exact distance of our eyes and then rendered on the fly to get perfect depth and convergence. Yeah, so basically you just have to deal with it for now. It's better than anaglyph, right?

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post #68 of 73 Old 04-17-2014, 12:01 PM
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Originally Posted by nenito2k View Post

interesting....my guess is that 90% of people that watch 3D encounter the big issues we are speaking about since the Opening of this topic....but people assume that these problems ARE part of the 3D, hence many people not liking watching movies and describing it as "head hurting"; unfortunately.....


I am afraid that's just not so.

The only 3D title I have seen that caused eye strain was A Turtle's Tale: Sammy's Adventures. The negative parallax on that title was so over the top that it was difficult and at times impossible for me to focus on the objects in front of the screen.
Almost all other 3D titles are fine. Sure, the odd shot is a bit off but nothing like as bad as the issue you seem to be getting.

I think the big clue is that non blood relatives watching a movie on the same equipment in your home have the same issue!
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post #69 of 73 Old 04-17-2014, 12:06 PM
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I think we're talking about different things. I should say vertical parallax. It's a known disadvantage of shooting with converged cameras and a direct result of keystone distortion.

 

No we're talking about the same thing, I was just incorrect about this. Image Distortions in Stereoscopic Video Systems

 

I still would like a comment from you on this aspect of it though: Keystone distortion (to whatever extent) is what we see with our eyes IRL right?


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post #70 of 73 Old 04-17-2014, 12:37 PM - Thread Starter
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I am afraid that's just not so.

The only 3D title I have seen that caused eye strain was A Turtle's Tale: Sammy's Adventures. The negative parallax on that title was so over the top that it was difficult and at times impossible for me to focus on the objects in front of the screen.
Almost all other 3D titles are fine. Sure, the odd shot is a bit off but nothing like as bad as the issue you seem to be getting.

I think the big clue is that non blood relatives watching a movie on the same equipment in your home have the same issue!

haha and yet....sammy is considered a reference 3D experience. I agree that is has issues...my eyes did bother me on many scenes mainly when people "move"....one there is no motion my eyes adjust and all is fine !

just saw FROZEN 3d bluray...and the experience was extremely positive...almost no ISSUES....just 1 or 2 quick scenes were foreground objects were not perfect for my eyes...nothing to even mention really
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post #71 of 73 Old 04-17-2014, 12:40 PM
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haha and yet....sammy is considered a reference 3D experience. I agree that is has issues...my eyes did bother me on many scenes mainly when people "move"....one there is no motion my eyes adjust and all is fine !

I don't think its reference, its way too extreme in my opinion. Some like extreme full on pop out and consider anything less to be not 3D but I disagree. Avatar was a reference quality release and negative parallax was rarely used.
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post #72 of 73 Old 04-17-2014, 12:43 PM - Thread Starter
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people calm DOWN !
CAMERON will reinvent 3D in december 2015....sit back and relax in the meantime ! that guy is a genius...no worries : http://www.brightsideofnews.com/2011/04/26/cameron-purchases-50-epic-cameras-will-avatar-2-announce-the-new-era-of-filmmaking/
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post #73 of 73 Old 04-17-2014, 07:09 PM
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Originally Posted by tgm1024 View Post

Keystone distortion (to whatever extent) is what we see with our eyes IRL right?

Yes, this makes sense to me too (though I'm not 100% sure, as there may be something to the fact that our eyes don't see rectangular images). But as with converged cameras, the distortion is only in the edges. IRL it would be permanently in our peripheral vision, where we can't really notice it. We certainly can't look right at it as we can in the artificial case of viewing a 3D display. If we move our eyes to focus and converge on an object that was in our peripheral vision, then the distortion on the object is gone because we changed the convergence of our "cameras."

That's the advantage of converged cameras, you get a very natural stereoscopic image as long as the viewer is focusing on what the cameras were focusing on. If the viewer's eyes wander around the image, then it's no longer ideal. Parallel is better in that case, because the viewer can look anywhere without any distortion that would be bothersome or uncomfortable. I would think that also means that everything (other than infinity where the cameras are pointed) looks subtly different than if you were to converge on things with your real eyes, but at least it's not a comfort issue.
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I read something about another format war in this thread, which I think is getting out of hand a bit: parallel vs. converged. First these aren't really competing formats, are they? They're just different techniques, and perhaps even the same rig is capable of both methods.

Exactly, there's no clear winner between the two because they each have their pros and cons. It all depends on what the director wants or what the application is (movies vs games for example). Two directors could argue about the two for days but neither would ever be 100% right. My comment about a new "war" was meant as a joke, as it's something we could debate endlessly if we're up to it, sort of like it was (is?) with active vs passive. The difference is that converged vs parallel isn't usually a decision we make ourselves.
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