In connection with the stereoscopic Walk pictures and 3D Telly, there was quite a discussion on aspects of vision!

 

Alec Bray

[Ed: in connection with viewing the Walk picture] You might have to “widen” the eyes…

Terry Meadowcroft

I love the 3D trees!

‘Widen your eyes’ can’t be did, except just the tiniest bit, and slowly, when you naturally have a very, very sight squint, and view a point at infinite distance (ish) like a star!

I know that, as an experienced star-watcher with a built-in squint (around half a degree), which I did not know about until a few years ago (I am coming up 75 now!).

On a lovely clear night on the North York moors, I noticed that a single flashing light on an approaching aircraft always appeared to be two flashing lights. Also. when looking at a dim single star, I could see two stars, and if I looked at the star for a long time, and totally relaxed, my eyes did make a slow divergence, and only after the best part of a second, managed to diverge to give the single star image. With the flashing aircraft light, my eyes did not have time to do the slow, uncomfortable and un-natural divergence, so appeared as two lights. 

I got a half-a-degree prism added to my glasses prescription, and that fixed it!

Of course, in nature the eyes have to converge to view a close object, so it happens as a natural thing, but there is no ‘further away’ than infinity, so divergence is never required so the musculature of the eye isn’t there to do divergence.

Thought you might like to know.

 

Alec Bray

Thanks Terry, for your … explanations!  I’m afraid my terminology was a bit loose!.  If you have ever looked at stereograms, the instructions tell you to “relax” your eyes.  It’s basically the same with the 3-D picture with no aids – you sort of focus your eyes differently.

I am not the best person to sort out any problems with the 3-D effect:: when I was at College, I taught myself to see 3-D image pairs without a viewer: Nowadays, if there is, for example, a “spot the difference” puzzle with two images printed nearly side by side and of a suitable size, I can see the two images – one with each eye –  and merge them into one – the differences then “shimmer” as the L and R images seem to switch in and out (I was going to say “vibrate” as that is what it more feels like.)

I, too, have prisms as part of my vision prescription. It’s fun going to the opticians, as the red spots wander all over the place …

 

Terry Meadowcroft

Hey, 3D viewing by crossing the eyes! I thought I was the only one daft enough – but it works; I can still do it!

I’ve been cheating at ‘Spot the Difference’ games for years – it’s great to see all the differences ‘flashing’ at you!

 

Keith Wicks

It’s possible to produce stereo pictures from ordinary video recordings. To do this, the camera must move horizontally between the selected frames. This is especially easy to do with some of the material taken from canal boats, which is currently featured regularly on TV.

The first shot below is a full frame picture, part of which I used for the LHS of the stereo pair. The boat from which the picture is taken is moving from left to right. I also selected a second picture, taken a few frames later, for the RHS of the pair. I cropped the two pictures to square format as the smaller images were easier for the unaided eyes and brain to combine to form a stereo view. But it’s always much easier using a stereo viewer with magnifying lenses. Long-sighted people may find strong reading spectacles helpful.

 

Alasdair Lawrance

That is really remarkable.  I found it really quite easy to create the 3d image.  I’d never heard of, or seen, that before.

 

Alec Bray

I just have to echo Alasdair’s comments.

There was some earlier discussion of “above” and “below” on stereoscopic pictures, so I had a go with a drone shot taken on the North Yorkshire Moors Railway (from the doco series on Channel 5).

This does actually work (although I think that the aspect ratios could be adjusted, and, of course, the number of frames between the two images ought to be calculated rather than my relying on a click on the pause button – and all the delays in my system while the interrupt is processed!!)

However,  I am not sure if the stereoscopic view really adds anything to the scene!  Yes, it shows “depth” and a “stereo” effect – and it would probably be better if both my eyes focussed correctly!

 

Alasdair Lawrance

I can’t make that one work, I suspect the images are too far apart in time.  I can only get about two-thirds of a coherent image.

 

Alec Bray

You are probably right!  When I looked at the images, there seemed to be such an angle between the two images that I was sure it wouldn’t work!

However, try this!  if I have a problem with seeing the “combined” images in these stereoscopic pictures,, I find that it becomes easier if the images are made smaller.  Here is a smaller pair, which I can “combine” without any aids.  Trouble is, it looks as if you are looking at a MODEL railway!

 

Nick Ware

One thing to bear in mind when selecting frames from a digital video source is Long GOP data compression. (Long Group Of Pictures compression).

Most high definition video is shot and/or broadcast this way, meaning that a frame (keyframe) is followed by a series of ‘difference’ frames, until the next keyframe is sent. So, in selecting your two stills, you would need to know when and which frames carried the full picture info (keyframes).

To put it simply, which is all I can do, it means that only the rapidly changing picture detail changes from one frame to the next. If the overall picture hasn’t changed (e.g. the background), there’s no point in sending it again for every frame.

In the analogue days, data compression wasn’t possible, so like film, every frame had to be complete. You couldn’t open the shutter and expose only the bits that had moved – a big advantage of analogue, you could argue! A huge waste of broadcast bandwidth though, in an age when the bean counters want as many channels as they can cram into the system, regardless of picture quality!

 

Keith Wicks

I can’t make the original drone pictures of the railway work with the unaided eyes either, although I expect everything would be OK using a stereo viewer. But I found it fairly easy once I had cropped the shots to a smaller, square format:

I think that getting only a partial coherent image from the original shots was to be expected as only part of the RH picture was covered in the LH picture. 

I don’t think there is much point in doing calculations in such cases. Just experiment with the original movie frames in the recording. The lateral separation between the viewpoints chosen will determine how much the depth effect is exaggerated. I remember, in a discussion on this mailing list, that the separation between TV cameras (at Wimbledon, I think) for certain stereoscopic shots was sometimes many yards. That would be OK in this case as all the objects in the picture are distant.

 

Mike Giles

Sitting at a sound desk doing sport at Television Centre which often involved quite long spells on the same source, I quite often found that my eyes had “relaxed” so that each eye had locked on to adjacent channels, rather than both being locked into the same channel as normal, which produced a remarkable 3D effect.

The first time it happened to me I wondered what on earth I was seeing until I put a finger our to tweak something, at which point I saw a double finger and realised what happened. Thereafter I could do it more or less at will, much the same as the published books of pages of seemingly mere patterns, which reveal hidden animals, vehicles, whales, etc., when you get your eyes “unlocked”. Some people seem quite unable to do it. [Ed: Stereograms]

 

Geoff Hawkes

When the so called “Magic Eye” 3D pictures [Ed: Stereograms] first appeared back in the nineteen-eighties (query), there was a large poster in a shop window with a notice saying “Can you see the dinosaur?” I looked and could see nothing other than the mishmash of small coloured shapes and dismissed it as a hoax. Some time later when the craze still hadn’t gone away I bought a book of such images and read the notes on how to view them in 3D. It took me a while but when I got the knack of how to do it, I was amazed at seeing the hidden 3D pictures. For some of them you need to let your eyes focus forward, i.e. to converge and others you need to focus back as though you were looking through the picture at a distant object, i.e. to let your eyes diverge. I’m still puzzled as to how the images are produced to make them work.

Now when I see anything with a repeating pattern on a table cloth or something like that, I amuse myself … by staring at it dreamily and can sometimes see parts of it apparently floating above the other.

…

It’s all fascinating stuff and another example of how our brains interpret what we see. Back in the nineteen-fifties I remember hearing about an experiment where the participants wore goggles which vertically inverted what they saw and how after a while their brains corrected it so they saw things the right way up again. Amazing or what?

 

Graeme Wall

Simple optics as we normally see things upside down and the brain learns to correct at a young age.

 

Dave Mundy

I also experienced a similar effect [to Mike Giles] looking at the sound desk in my scanner but the images seem to be enlarged, when I brought the eyes back together it all went further away! Looking at my monitor now I can ‘split’ my eyes and see two images about 2″ apart e.g.  ‘before lunch as well before lunch as well’. PS. It happened before lunch as well!

 

Nick Ware

Me too. I’ve always found that phenomenon rather intriguing.

 

Mike Giles

Yes, Dave, I agree that besides the stereoscopic effect, everything did seem to be enlarged. I often use subtitles on the TV after my wife has gone to bed, as there is so much mumbled speech nowadays that it needs to be reasonably loud to catch all the asides, and very often the text appears to be in a different plane from the picture ~ almost as if they are on a separate screen very slightly in front of the TV.

 

Dave Mundy

Funny that, I once saw some red text on my monitor and it was definitely on a different plane to the picture!

 

Roger Bunce

When we put up some new wallpaper in our living room, it seemed to do nasty things to our eyes. The problem was that it was a small dot pattern, and the spacing between the dots was roughly the spacing between your eyes. So, your eyes could find themselves looking at different dots, while your brain assumed they were looking at the same dot. This was fine, until you looked away, when you got an unpleasant sensation of your eyes being sucked out of your head! Now that the wall paper is no longer new, and we no longer bother to look at it, the problem has gone away.

The enlargement effect – I think I can see a logic there – triangulation. If your eyes are looking nearly parallel, then your brain might naturally assume that you are looking at something far away. If your eyes are more convergent, then it might assume that you are looking at something close. So, if the image believed to be far away, appears to be the same size as the image assumed to be close, then your brain might explain this to itself by assuming that the far away object is larger. (Does that make any sense? I know what I mean even if I haven’t explained it very well!)

 

Alan Taylor

I’ve never been comfortable with stereoscopic photography being referred to as 3D… “Stereoscopic” is the correct term when two images are used to create a depth illusion, but it’s not 3D. 

[Ed: Alan’s full contribution is on the “3D Telly” page: apologies for the title, Alan]

 

Pat Heigham

The fact that we perceive stereoscopic vision only in the horizontal plane must be because our eyes are side by side (horizontally). To perceive vertically, would we need two further eyeballs, one above the other? Or would tilting one’s head sideways do the trick?

(I visualise a “Dr. Who” creature with four eyes!).

I brought in my stereo viewer to show the crew some examples. Peter Wineman (Sound Supervisor) remarked that it wouldn’t work for him, as he only had one eye! We never knew!

 

Dave Mundy

I thought it was common knowledge the Peter Wineman had only one working eye which is why he couldn’t operate a boom very well and ended up in the office! He said he played cello in the Guards orchestra so I suppose one eye is good enough for that! (Chris Eames would know more).

 

Alan Taylor

With “3D” television images, you can peep round things by moving your head a little to one side or the other and the image reflects that slight change of viewpoint in a natural way, but if you were to move your head up or down by a similar amount, you observe no corresponding change in the vertical axis.

When I view stereoscopic images, they look to me rather like a series of flat planes, much like the way that in an opera house, the impression of depth is created by having flats hung at different distances from the proscenium arch. When I view the real world, it’s a true 3D Image with subtle graduations. Stereoscopic images create an excellent impression of depth, but they rarely look exactly like the real world to me.  I don’t understand why that is because in each case I’m viewing with exactly the same number of eyes.

We’ve only got two ears, but can perceive sound as coming from above or below, so I think there’s more going on with our perception of vision and sound than meets the eye (or the ear ).

 

Dave Plaice

I’ve always thought the “series of flat planes” effect of stereoscopic images (starting with View-Master) is because we are looking at flat images a fixed distance away, whereas in real life we’re looking at objects at various distances. Our eyes would be focusing and refocusing on these which would give the brain more depth information.

 

Chris Woolf

The problem is that stereo or “surround” audio, and 3D pictures are only a simulation of depth from one viewpoint. They are depth effects – not the real thing. You cannot move your viewpoint and see something new.

Wavefield synthesis gives an eye-opener into true 3D audio – not perfect yet, but you can actually walk around a space, turn round, and have every sound stay where it should be – and even have sound from beyond the boundary of the speakers.

Generating 3D images from laser-scanned spaces does allow something similar – you can move anywhere within the virtual space and see behind objects as well as from the front. These techniques are ~true~ surround ones, giving you the freedom to move about without restriction, but the data complexity of this sort of stuff is frightening.

Nor are these techniques much use in a lot of entertainment – for this we usually prefer the proscenium arch approach where we see and hear something specifically from the “director’s” chosen viewpoint. The attempts to change this – books that can be read in any chapter order, dramas that allow the audience to choose the outcome of a story etc, have never proved terribly successful, for good reason.

 

Pat Heigham

I like the proscenium arch, dislike theatre in the round.  I get unnerved when actors leave the stage and advance into the auditorium.  They are invading my space, I’ve come to watch them, not to be part of the show.

Don’t think it would go down too well if I climbed onto their stage?

 

Bill Jenkin

I know what you mean about being/not being on stage with them. 

I had the misfortune once of seeing a production of “Julius Caesar” at Stratford on Avon which was very much in the round and we were in seats that were actually on the stage,  literally.  I was apprehensive about being included in the action somehow but the worst thing was that for obvious reasons I found myself directly in the actor’s eyelines,  which was something we had tried to avoid for years working on dramas in the studio. So I found myself desperately trying not to look at them for fear of “I’m sorry, there’s someone in my eyeline”. 

That did happen to me once at work while eighting up a camera cable outside a set when Dan Massey gazed out through the window as part of the action and saw me!

 

Chris Woolf

Yes, that is very awkward.

I was in a small audience for a very well known poet who was reciting a 30 minute piece from memory.

After the event she took me aside and said she was sorry I’d found it boring.  “Boring? Why on earth would you think that?”, I asked.  “Because you were looking down and I assumed you were texting for the whole thing…”

Ha! No! Not a bit of it. It’s just that a life-time of training makes me always avoid an eyeline.

 

Nick Ware

Even a proscenium arch doesn’t necessarily mean you’re safe. I once had comps for the Christmas Panto at Wimbledon Theatre. If I’d paid for the tickets I definitely wouldn’t have had centre front row stalls seats. But there we were, and Ken Dodd, who I had been working with a number of times, recognised me, and calling me by name, taunted and teased me mercilessly. I won’t make that mistake again!

 

Hugh Sheppard

With cable-clearing done, in days long ago, I stayed on the studio E floor at Lime Grove for “Panorama”.  Richard Dimbleby was interviewing a very nervous Sir Alec Douglas-Home, the P.M.  Standing n front of the MR boom, I was all too in line behind Dimbleby, so that the P.M.’s gaze alighted on me as he spoke on government policy or whatever. I was transfixed; to look away seemed so disrespectful that I couldn’t do it, so stayed like a rabbit n the headlights. Worse, I tried to look interested … then nodded in agreement once or twice… it was awful!  After it was over, I moved away and found something to do – but as Sir Alec left he again caught my eye and waved goodbye…

 

Peter Fox

Hugh’s PM Douglas-Home story reminded me that Marti Webb, when we were recording the ”Songwriters” musical series, in 1978, in her early TV days before ”Tell Me On A Sunday”,  said that she couldn’t really cope with the idea of thousands if not millions of people beyond the glassy eye of the camera. She said that to make it work for her she was just singing to the cameraman. We made sure she gots some cheery smiles.  Now that made it rather special. Nice to think we were helping her to get started in Telly.

She remained on friendly terms for years afterwards. Gerry Tivers arranged for Ron and I and himself of course, to meet up with her after we went to see her in TMOAS in Windsor, probably in 2004, and she still knew exactly who we were .  And so, Alec DH was probably also grateful for a human being to relate to rather than the vague concept of a vast invisible audience. That’s why you got the cheery wave, Hugh,  you probably saved the day.

 

Pat Heigham

Having been fortunate to have had a private tour of the IMAX cinema at Waterloo, we discovered that there were a series of vertical loudspeakers to direct the audio ‘up and down’ as well.

Multiple sound tracks off computer, locked to the projectors.

What was interesting was that should the film suffer a break, it had to be repaired with black frames inserted, to keep the length the same – it wasn’t possible to edit the computer audio track! Don’t see why not.

When I was playing with projected stereoscopic slides, it was possible to adjust the picture so that it appeared to be beyond the screen – one felt like going up and peering over the edge. Or, to bring the image out in front of the screen, this is used by IMAX, and is incredibly effective.

In mono IMAX, what works best are wide shots from aerial cameras: a demonstration reel had some clips from a drama – facial CUs, the height of three London double-deckers just didn’t look right!

The IMAX visit was facilitated thanks to AMPS member Anthony Faust who had mixed many of the IMAX films.

Alan’s ‘flat plane’ perception could be similar to the reaction of a remote tribe, somewhere, who were shown film of the footage shot. They didn’t understand why they were being shown a succession of still pictures. Which leads to the explanation and another old joke:

‘…Marilyn Monroe’s wiggle doesn’t exist – it’s called ‘persistence of vision!…’