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post #1 of 4 Old 03-07-2017, 02:36 PM - Thread Starter
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Question 3D Display for vision experiments

Hello guys!

I am currently doing a neuroscience course and doing some vision study projects.

Therefore I wonder whether you guys have some good ideas on which 3D projectors to use for vision experiments.

Since it's used for experiments, I was concerned that the ones used for movies might not reach the standards, and is that the case?

One of the projectors that I was looking at was the Optoma HD141x, but I am not sure whether that's good enough.

Essentially the applicable models should be either full 3D or 3D ready, and should be able to support experimental software packages like MATLAB PsychToolBox.

It should work with 3D glasses (to be found) and gives minimum leak between left and right eyes.

It should also have a relatively short response time and should not despair (artificially improve its quality or contrast) any of the images we produced.

An example experiment could be like: <Attention capture by eye of origin singletons even without awareness—A hallmark of a bottom-up saliency map in the primary visual cortex> on journal of vision .

Any idea or suggestion will be appreciated!
Thanks
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post #2 of 4 Old 03-08-2017, 11:53 AM
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The perfect type of 3D display you are looking for does not really exist. The closest would be a head mounted display.
As far as projectors go, all of them must do some type of compromise to produce their 3D image which may interfere with the experiment you are trying to run. (depending on the hypothesis you are trying to test)

Typical 3D projectors use the active shutter glasses technique. They allow the projector to be cheap and allow any screen to be used. The glasses contain electronic LCD shutters that either allow light or block it in each eye in sync with projector. There are multiple synchronization protocol between the projectors and the glasses. You have to check the projector's manual to see which are available and which type of glasses you need.
As far as image quality goes : DLP projectors offer less crosstalk (superior image separation) than LCD projectors, due to their much faster response times, and is the preferred way to do 3D.
There are disadvantages though :
-Active systems display the left and right eye views sequentially, which is not natural : it creates a flicker effect, in addition to slightly offsetting the depth perception of moving objects.
-The active system requires mandatory processing of specialized hdmi formats by the projector (introduces input lag) or requires specialized type of input (frame sequential) which is being phased out.
-DLPs may suffer from rainbow effect since the primary colours are displayed sequentially. Not everyone can see the effect, but you should know that it exists.

If your experiments may be skewed by the disadvantages of active projectors, then you may want to take a look at passive systems.
The gold standard of passive projection is dual-projectors. It is however very rarely used due to the very high cost, since it requires 2 projectors and special support equipment.
There are two ways to do it :
-polarized which gives the best results but requires investment in a specialized screen capable of maintaining the polarisation of light. Even with the best professional screens, you will still get some crosstalk (non perfect image separation). The glasses need to match the polarizers type and angle configuration you have chosen (there are a few shops online selling custom glasses with multiple polarizer configurations)
-narrow band multi-colour filters (Dolby3D, Infitec,Omega Optical) which break the colour balance and often require heavy colour processing (with some consumer projectors, the colours can sometimes not be recovered). These types of filters are of reflective type and must be used in total darkness or the user will constantly see the reflection of his own eyes in the glasses. (and the glasses are proprietary)

The next best option for passive display is a large flat screen LCD TV equipped with FPR technology.
The user wears passive polarized glasses and sees both eye views simultaneously which grants the most comfortable and flicker-free 3D image.
The TV can be fed the standard hdmi 3D format with processing, but can also be fed a native 3D image directly (required you to disable all image treatment in the TV to make sure it does not interfere with your 3D image)
The glasses are polarized and generally used the same standard as the RealD 3D cinema glasses (there are exceptions, most notably the few 3D FPR computer monitors, but then the manufacturers will provide their own glasses).

The disadvantages of FPR TVs are :
- It's for TV only (cannot be used for projection) since the film pattern needs to be applied directly on the surface of the display and must be pixel perfect aligned.
- It has a sweet spot : the user must sit at the correct height and distance relative to the TV, viewing from outside the sweet spot creates massive crosstalk
- Even at the sweet spot, crosstalk still exists (stereo image separation is far from perfect), but at least the passive bleed is predictable and as long as you are not using 100% contrast test scenes (trying to display bright pattern of a perfectly black background) you can work around it
- It halves the vertical resolution and every other line becomes a black line : the lines are visible from the usual living room TV<->couch distance on 1080p sets. But things are much better with 4K TVs, which is why 4K passive TVs are currently considered to be the best 3D displays for the buck at the moment.

4K TVs with FPR 3D technology are easy to find at the moment but manufacturers have announced they'll stop production this year in order to implement 2D HDR.
So if you want one, you need to buy one this year or it will be too late.
Jason Zhang likes this.

Passive 3D, forever !
My Full-HD dual-projector passive polarised 3D setup. (really out of date ! I need to update it some day...)


Last edited by BlackShark; 03-08-2017 at 12:10 PM.
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post #3 of 4 Old 03-08-2017, 01:51 PM - Thread Starter
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Hi BlackShark,

Thank you so much for your reply!!

The disadvantages of the active systems seem slightly worrying but it might not be that significant unless our experiment is highly quantitative.

One example setup used previously was:

The stimulus was presented on a Clinton Monoray monitor, at a frame rate of 150 Hz, viewed at a distance of 40 cm in a dim room, with the FE-1 shutter goggles from Cambridge Research Systems. The shutter goggles, with 25% open shutter transmission, 100 μs shutter open–close switching time, and a 500:1 ratio for open:close transmission, let left and right eyes view the temporally alternate frames on the screen, so that each eye views 75 out of the 150 frames each second without any sensation of flicker. Each test stimulus display had 660 bars spanning 34° × 46° in visual angle. Each bar was a rectangle of 0.12° × 1.1° in visual angle, sitting on a regular grid of 22 rows by 30 columns. In Experiments 1 and 4, and for subject EC in Experiments 2 and 3, the location of each bar was randomly jittered horizontally and vertically by up to 0.12° in visual angle. The jitter was to prevent the possibility of an accidental wall paper illusion (which indeed was never reported by any subject), and the results do not seem to depend sensitively on this jitter. A bright dot of size 0.12° × 0.12° sat at the center of mass of each group of four neighboring bars. A disk of 0.5° in diameter sat at each of the four outer corners of the rectangular array of texture bars. A fixation stimulus contained a central fixation point of 0.3° in diameter, together with the same four outer disks in the test stimulus. All the disks and dots, the fixation point, and the instruction text such as “press a button for the next trial” were identical in both eyes, serving to anchor vergence on the display screen. These stimuli were 48 cd/m 2 in brightness, and the background was black. Each stimulus bar was presented to one eye only or, in one stimulus condition of Experiments 2 and 3, identically to both eyes. To present a bar of any particular luminance to one eye only, its luminance alternated from zero luminance in one video frame to double luminance in the next. Without the stereo goggles, a bar appeared equally bright on the screen whether it is presented in the monocular or binocular mode. None of the observers who passed our stereo depth test (see Participants section) reported experiencing binocular rivalry or stereo depth with any experimental stimuli.

and do you think that might be feasible using an active system?

Thank you very much indeed!

Quote:
Originally Posted by BlackShark View Post
The perfect type of 3D display you are looking for does not really exist. The closest would be a head mounted display.
As far as projectors go, all of them must do some type of compromise to produce their 3D image which may interfere with the experiment you are trying to run. (depending on the hypothesis you are trying to test)

Typical 3D projectors use the active shutter glasses technique. They allow the projector to be cheap and allow any screen to be used. The glasses contain electronic LCD shutters that either allow light or block it in each eye in sync with projector. There are multiple synchronization protocol between the projectors and the glasses. You have to check the projector's manual to see which are available and which type of glasses you need.
As far as image quality goes : DLP projectors offer less crosstalk (superior image separation) than LCD projectors, due to their much faster response times, and is the preferred way to do 3D.
There are disadvantages though :
-Active systems display the left and right eye views sequentially, which is not natural : it creates a flicker effect, in addition to slightly offsetting the depth perception of moving objects.
-The active system requires mandatory processing of specialized hdmi formats by the projector (introduces input lag) or requires specialized type of input (frame sequential) which is being phased out.
-DLPs may suffer from rainbow effect since the primary colours are displayed sequentially. Not everyone can see the effect, but you should know that it exists.

If your experiments may be skewed by the disadvantages of active projectors, then you may want to take a look at passive systems.
The gold standard of passive projection is dual-projectors. It is however very rarely used due to the very high cost, since it requires 2 projectors and special support equipment.
There are two ways to do it :
-polarized which gives the best results but requires investment in a specialized screen capable of maintaining the polarisation of light. Even with the best professional screens, you will still get some crosstalk (non perfect image separation). The glasses need to match the polarizers type and angle configuration you have chosen (there are a few shops online selling custom glasses with multiple polarizer configurations)
-narrow band multi-colour filters (Dolby3D, Infitec,Omega Optical) which break the colour balance and often require heavy colour processing (with some consumer projectors, the colours can sometimes not be recovered). These types of filters are of reflective type and must be used in total darkness or the user will constantly see the reflection of his own eyes in the glasses. (and the glasses are proprietary)

The next best option for passive display is a large flat screen LCD TV equipped with FPR technology.
The user wears passive polarized glasses and sees both eye views simultaneously which grants the most comfortable and flicker-free 3D image.
The TV can be fed the standard hdmi 3D format with processing, but can also be fed a native 3D image directly (required you to disable all image treatment in the TV to make sure it does not interfere with your 3D image)
The glasses are polarized and generally used the same standard as the RealD 3D cinema glasses (there are exceptions, most notably the few 3D FPR computer monitors, but then the manufacturers will provide their own glasses).

The disadvantages of FPR TVs are :
- It's for TV only (cannot be used for projection) since the film pattern needs to be applied directly on the surface of the display and must be pixel perfect aligned.
- It has a sweet spot : the user must sit at the correct height and distance relative to the TV, viewing from outside the sweet spot creates massive crosstalk
- Even at the sweet spot, crosstalk still exists (stereo image separation is far from perfect), but at least the passive bleed is predictable and as long as you are not using 100% contrast test scenes (trying to display bright pattern of a perfectly black background) you can work around it
- It halves the vertical resolution and every other line becomes a black line : the lines are visible from the usual living room TV<->couch distance on 1080p sets. But things are much better with 4K TVs, which is why 4K passive TVs are currently considered to be the best 3D displays for the buck at the moment.

4K TVs with FPR 3D technology are easy to find at the moment but manufacturers have announced they'll stop production this year in order to implement 2D HDR.
So if you want one, you need to buy one this year or it will be too late.
Jason Zhang is offline  
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post #4 of 4 Old 03-08-2017, 05:15 PM
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The description of the system you quoted is an active display with shutter glasses.
You should be able to perform similar experiments.

There is a difference in the control of the hardware. The display you are quoting is a professional display which the experimenter can tune to anything he wants.
You will be working with consumer hardware which characteristics are designed to match consumer stereo content and which you cannot change.

The projector you are considering (Optoma HD141x) operates at 120Hz when displaying 3D content.
Which means it displays 60 images per second and per eye.

The 3D signal inputs are restricted to the usual consumer hdmi1.4a formats, which means the projector does not provide you with any way to display the exact pure image you are sending. You will always get some amount of processing. You'll have to choose one according to the needs of your experiment.

-Hdmi frame packing 720p60 : the picture resolution does not match the display's resolution. The projector will upscale your picture using it's own logic.
-Hdmi frame packing 1080p24 : the refresh rate does not match the display's refresh. Your content can only be updated at 24Hz, the projector will upsample internally to 120Hz using it's own logic.
Some consumer devices lower the refresh rate to 96Hz in this mode in order to keep the frame order constant between the eyes but don't tell you about it.
-Side by side 1080i60 : the picture needs to be transmitted interlaced, The projector will perform deinterlacing using it's own logic (combined spatial and temporal interpolation). In addition to the picture resolution not matching the display's resolution (1/2 resolution horizontally). The projector will upscale your picture using it's own logic.
-Side by side 1080p60 : Unknown. Many hdmi1.4a displays also support this without claiming it on the manual. The projector will upscale your picture using it's own logic which you do not control.
-Side by side or Top/bottom 720p60 : the picture resolution does not match the display's resolution (1/2 resolution horizontally or vertically) + the second upscale from 720p to 1080p. The projector will upscale your picture using it's own logic which you do not control.

In order to use Hdmi Frame packing mode, your image playback software will need to make use of the special 3D video output of your graphics card.
I am not familiar with MATLAB PsychToolBox. I do not know if it supports this type of output.
Side by side and Top/bottom have the disadvantage of dividing the image resolution by 2 (stretch along one of the axis of the picture). But have a massive compatibility advantage of working with ANY video or image software since it's using traditional 2D transmission.

The exact characteristics of the shutter glasses are not known.
The projector is equipped with DLP Link and a VESA 3D sync port, so you'll be able to choose any transmission and glasses you like.
The difference between these transmission technologies is : DLP link uses visible light for transmission (uses a "white flash") which the shutter glasses are supposed to hide to the user, whereas other types of transmitters/glasses use non-visible transmission (IR light or RF radio).

Passive 3D, forever !
My Full-HD dual-projector passive polarised 3D setup. (really out of date ! I need to update it some day...)


Last edited by BlackShark; 03-08-2017 at 05:22 PM.
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