[visionlist] CRT monitor solutions

Tue Oct 27 10:44:02 PDT 2009

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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