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Discussion Starter · #1 ·
The below are short excerpts from 'extremetech.com'. interesting site:


It seems to explain why some have observed excess blurring

during moving images. Also mentions contrast.

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Speed

LCD displays have an inherent lag between the time that a cell is switched, and the time that the

change is visible. This is a result of the fact that the liquid crystals must actually move within the cell,

and this movement takes time. This puts LCDs at a distinct disadvantage compared with CRTs (and DLPs) when

displaying fast-moving images, such as scrolling data or movies.

___________________________________________________


DLP:

One advantage of these panels is that they have extremely fast response times. It is possible to

have individual pixels turn on or off many times during the projection of just one image frame. This

makes it possible to create a full-color image with one panel, using a field-sequential procedure.

First, green light shines on the panel, and the mechanical mirrors are adjusted to display the

green pixel data of the image. Then the mirrors are adjusted again for the red and blue pixel data

of the image. (Some projectors get extra brightness by using a fourth, white field to add more

light to the white and lighter shades of colors in the image.) All this happens faster than the

human eye can see, and the separate fields are combined in the brain where they are perceived

as a single, full-color image.


DLP panels have high resolution and have proven to be extremely reliable. They also have roughly

twice the contrast of polysilicon LCD projectors, making them more effective in bright room settings.


Disadvantages

There are few problems with DLP, but they are more expensive than polysilicon panels.

Field-sequential images can appear to break up into different colors if you look from one spot on

the screen to another, especially if the image has small white objects on a black background. In

projector applications, the motor used to spin the color wheel can be a noisy distraction, but

there are new, solid-state color filter systems coming on the market that are silent, which would

eliminate this problem.

____________________________________________


LCOS:

Panels are of moderate cost with relatively fast response times. It is

possible that the prices for these panels could be reduced greatly, especially if demands permits

production in large volumes.


Disadvantages

One of the weaknesses of LCOS displays is that they do not have the high contrast seen in DLP

images. Some are designed for field-sequential illumination--as used with single-panel DLP

applications--but others either rely on combining the image of three separate panels, or use color

filters and triple the number of pixels for a given resolution.


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Jim Story

Live long and Prosper
 

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Hmmm...I just saw some LCOS at InfoComm with over 1000:1 contrast and they looked phenomenal (D-ILA).
 

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Bravo Morbius. This article clearly internal consistency problems.


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STOP HDCP on DVI

Don O
 

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Discussion Starter · #4 ·
I know..., it's difficult to know who/what to believe!


Best to depend on your own eyes/ears.


The article was by "Alfred Poor", I don't know his background, he writes lots of stuff on displays on that

web site.


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Jim Story

Live long and Prosper
 

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I think I've seen Alfred Poor's name on a regular technical column in PC Magazine. He seems to know his way around pcs, but I don't know if he has expertise in projector technology.


Al
 

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What disturbs me about this article is the lack of quantititative information whcih makes it misleading to the newbie.


I have never noticed, for example, any perceptible time lag with my LCD. JVC LCOS with 1000:1 contrast under certain conditions has been discussed ad nauseum in this forum .


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Ken Elliott


[This message has been edited by kelliot (edited 06-30-2001).]
 

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I would take this article with a BIG grain of salt.


The first part states that it takes time for the crystals

to move in LCDs which makes them slow. The reorientation

of molecules can be quite fast.


Then the article states that DLP mirrors are very fast.

Well the mirrors in a DLP are many orders of magnitude

larger and heavier than liquid crystals in an LCD.


Finally, the article states that LCOS is "relatively fast".

Well the LCOS is an LCD with a mirror on one side so that

the light isn't transmitted through the device, but enters,

reflects, and leaves via the same face it entered.


How is an LCD slow, while an LCOS is fast?

This article appears to be internally inconsistent in

its definitions of fast and slow.


As far as contrast is concerned, I believe Tom Stites of

JVC has explained that the problem of contrast, i.e. of

obtaining low enough black level is more a property of the

optical design of the projector. It's difficult to totally

disipate the unwanted light from the lamp inside the PJ.

Nothing is perfectly black - and the light eventually finds

its way out the lens.


Greg
 
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