[visionlist] CRT monitor solutions: 3-chip DLPs

Duje Tadin duje at cvs.rochester.edu
Wed Nov 4 07:20:52 PST 2009


Dear visionlist,

While DPL projectors with a color wheel (i.e., single chip DLPs) are  
clearly not a good solution for psychophysics, 3-chip DLPs are worth  
considering - especially models that are designed for active stereo.  
These models have a 120Hz frame rate and due to their active stereo  
use, have reliable frame timing. The cost, however, runs around  
$40,000. I'm in a process of buying one from Digital Projection for  
our fMRI set-up -- and should have more updates after we do some  
initial testing.

Duje Tadin




On Oct 27, 2009, at 1:44 PM, Daniel Reetz wrote:

> Hi Deborah, Visionlist,
>
> I have been actively researching future displays for the last three
> years, in part to get to the future of high dynamic range imaging (I
> work in a lab that studies Brightness, a high-frequency capable HDR
> display is one of our white whales).
>
> As you know, most LCDs are unsuitable for time-critical work. This is
> unlikely to change, as most technologies that accelerate the temporal
> response are aimed at gamers and perform in unpredictable ways, or use
> algorithms/techniques that are trade secrets and a PITA to reverse
> engineer. Additionally, most LCD panels (including, at this time,
> every Mac laptop panel) are Twisted Nematic (TN) panels, which are
> only capable of 6 bit color, or worse, do some kind of temporal
> dithering/screwing around to give the appearance of 8 bit color.
> In-Plane-Switching panels have usable color, and there are even
> ten-bit options (12 often claimed in medical grayscale LCDs) but the
> temporal performance on IPS panels is worse than TN. Both exhibit
> slight differences in the time to move from one "gray" to another
> "gray" versus moving from white to black. Recently, the CFL backlight
> tubes of LCDs are being replaced with LED arrays. These LED arrays
> illuminate the edge of a laser-engraved piece of acrylic which is
> supposed to make a homogeneous white field for the LCD to filter. LEDs
> do allow for more careful wavelength selection, to better match the
> bandpass characteristics of the front panel, and sometimes can extend
> the gamut beyond sRGB or NTSC, but they do nothing for the temporal
> properties of the front panel. There have been prototypes of LCD
> displays with AMOLED panels behind them for illumination. This has the
> advantage of being extremely high contrast, but the crossed-polarizers
> inherent to LCD technologies make the transmission rate extremely low;
> the luminance from these AMOLEDs would be reduced by almost 90%.
>
> To evaluate the temporal characteristics of monitors generally, I have
> used instruments ranging from homemade junktronics like a photodiode
> connected to a sound card, to a high-speed video camera. The high
> speed video camera provides very good diagnostic information when
> evaluating monitors. With the 1200hz sampling available on some Casio
> cameras, it is possible to see the backlight pulsing on and off, or to
> see the scanlines on a CRT. There are some issues with the "binning"
> that the camera is doing to obtain such high sampling rates, but it is
> good enough to see major problems with most monitors with nothing more
> than visual observation.
>
> As for extant technology:
>
> You can throw DLP projectors out for nearly any speed-critical task,
> as they do all kinds of weird processing. The problem here is that
> they have a monochrome MEMS imaging element, and they have to pass it
> through a color filter wheel to produce color temporally. This wheel
> also has a clear element, which is used to jack the brightness in some
> areas of the display, but it doesn't necessarily refresh the image
> over the entire imaging area every time. In our Dell 5100mp it is
> updated piecemeal. If you must use DLP, you should use a high-speed
> camera or other sensor to check that your stimuli are being presented
> as you think they are.
>
> LCD projectors are better, but not much better.  Hit or miss.
>
> I've recently had some success with the 3-chip LCoS  projector (a
> hybrid between LCD and reflective technologies) that came with our
> eLumens Visionstation. Although it is low-contrast  and the luminance
> sucks (60cd/m^2 max), so far the temporal properties on gratings look
> good at lower frequencies like 30 hz. No artifacts or tearing. LCoS
> might be a good solution in the near term for slower stuff. Our
> projector is a JVC SX21. It may be that the new projectors are much
> better, but I would check to make sure that their claimed "15000/1"
> contrast ratios are not the result of using a variable aperture. Any
> contrast claim over a few hundred to one is probably some nasty trick
> like that. Ensure that you can disable it, in software or by yanking
> the cable internally.
>
> Getting to the point, the future of displays generally will likely be
> OLED, LCD (it's so cheap and established that it is not likely to go
> away), or TMOS.
>
> OLED does not  (yet) offer much hope, in my opinion. OLED panels like
> in the small Sony display are typically driven in patches. By this I
> mean that the whole display is subdivided into smaller grids which are
> driven by individual processors, much like in commercial LED signage.
> The timing between these sections is not guaranteed, or may be
> sequential, left to right, top to bottom. If timing is not important
> to you, the contrast of an OLED display is rather good. This is
> because you can actually turn off the little OLED at whatever
> location, and it's hard to get blacker than that. The brightness
> problem with these displays is a thermal issue. To get the LEDs as
> bright as they can go, you must dissipate tons of heat from a very,
> very small area. If you do not dissipate the heat, there is a thermal
> runaway condition where the OLEDs will destroy themselves. As a
> result, I do not see small-pixel OLED displays getting to be much
> brighter than a few hundred cd/m^2 until there are a few more
> breakthroughs in OLED efficiency, or active cooling. This held with
> the small Sony panel that I saw in person. It was clearly not very
> bright compared to the TN LCD panels around it, though admittedly the
> colors and contrast looked very usable. Additionally, the Sony XEL-1
> was basically a little Linux computer (running BusyBox, I think) which
> is just another layer of crap to hack to get your stimuli onscreen
> (though admittedly, Linux is vastly more hackable than Windows or
> Mac).
>
> Now the other technology that I mentioned is called TMOS. It was just
> recently announced, it is a brand new type of display that relies on
> MEMS technology, like DLP. Personally, I am very excited about this
> technology. The first thing that it has going for it is that it needs
> no new fabrication facilities. It can be made in ordinary LCD
> fabrication plants. That means the time-to-market should be short
> relative to OLED, which is still not cheaply or widely available. TMOS
> means "Time Multiplexed Optical Shutter". Basically, it is a display
> scale DLP device. Each pixel is a little mirror, capable of 2
> microsecond on/off times. They are situated above a backlight/FTIR
> light pipe which is being lit with LEDs that are modulated extremely
> quickly. Color is generated by flashing the mirrored element on and
> off over this blinking backlight as it transitions from R to G to B.
> Early claims from engineering/marketing people are 300hz refresh
> rates. If they meet 20% of that, we won't be doing too badly. And for
> those of us who study vision without color, that backlight can be
> comprised of only white LEDs, allowing for very, very good temporal
> resolution. In addition, the time-critical nature of this display
> (meaning, that the backlight must be refreshed exactly with the
> mirrored pixels, unlike LCD or LCoS, but like DLP) should presumably
> mean that timing is taken seriously with respect to input as well,
> though, since I have seen/analyzed no prototypes, this is just wishful
> thinking/speculation.
>
> I think LCoS may be a good interim solution (especially because JVC is
> trying to work with the high-end market, see , and TMOS may be the
> best future solution. Perhaps the vision community could get in touch
> with UniPixel or Samsung (the TMOS people) and play with
> prototypes/help guide development. It seems that all of us could use a
> standard display with good luminance, 200:1contrast, and fast temporal
> response (reliable 60hz, 8bit per primary), but furthermore, we could
> all use purpose-built displays. Because the TMOS technology is simply
> on-off at its core, there is no reason not to support, for example,
> more than three primaries, infrared plus RGB, or two whole different
> color sets defined by two different sets of primaries. (A photopic and
> scotopic display in one!). People interested in color could select
> their primaries of interest, and people interested in time could
> select fewer primaries to optimize temporal properties. Furthermore,
> since TMOS is completely digital, maybe we can get rid of all those
> nasty analog processors and drive the things ourselves, directly over
> DVI, or some other digital interface. Removing the analog-digital
> conversion step (with all the associated hardware voodoo/signal
> processing) would be a boon to vision researchers everywhere.
>
> In my mind, this is a technology that has the potential to be a magic
> bullet for vision research.They're talking about releases in Q1 2010.
> If you are at all interested, I hope you'll consider making the
> desires of the vision community known to them so we don't lose another
> interesting display down the "cheaper faster crappier" consumer-tech
> plug hole.
>
> Regards,
> Daniel Reetz
>
> PS. Their approach to color-breakup problems is interesting:
> http://www.wipo.int/pctdb/en/wo.jsp?wo=2007016511
>
>
> On Mon, Oct 26, 2009 at 7:51 PM, Deborah Apthorp
> <deboraha at psych.usyd.edu.au> wrote:
>> Hi all,
>>
>> I'm currently looking into purchasing some high-end CRT monitors  
>> for our
>> psychophysics lab. So far I am having a great deal of trouble  
>> finding anyone
>> who is still manufacturing CRT monitors, and the refurbished Sony and
>> Mitsubishi models we have are slowly dying. CRS only sells theirs  
>> as part of
>> the Visage package. My only lead so far is for a refurbished Fimi  
>> MGD 403
>> grayscale monitor for $3200 (ex-medical, I think). Has anyone found a
>> reliable supplier, or is there going to be a viable alternative to  
>> CRTs (for
>> instance, OLEDs?) in the near future? Otherwise, what are old-school
>> psychophysicists going to do? I would be very interested to hear  
>> opinions on
>> this.
>>
>> Thanks,
>>
>> Deborah Apthorp
>> _______________________________________________
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>>
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------------------------------------------------------------
University of Rochester
Dept. of Brain & Cognitive Sciences / Center for Visual Science
http://www.bcs.rochester.edu/people/duje/home.html
Office: 585.275.8682 Fax: 585.271.3043 Lab: 585.275.7259
Email: duje at cvs.rochester.edu
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