[tig] HDnet You gotta read this!!!

Martin Euredjian ecinema
Fri Apr 2 03:21:31 BST 2004

James DeLuca wrote:

> PC graphics card/monitor display can run at 1600 x 1200 at 72Hz.
How expensive are they?

Right.  A few points:

- More than likely you have an analog RGBHV interface.

- Those chip sets are special purpose and cannot do video

- At 1600 x 1200 you can have the semblance of resolving that level of
detail.  At 1920 x 1080, not a chance with a CRT.

- The interface being analog, you have to ask yourself just what you are
looking at when you evaluate cost.

- I've learned that the reported frame rate (by a PC/Mac control panel
application) isn't necesarily the frame rate at which the monitor is
actually running.

These chip sets can't really be used to build monitoring systems.  I wish
one could.  They are designed primarily as PC graphic engines, without much
concern for the needs of the video world.  For example, you can't pump a PsF
signal into them and expect anything in return.  So, althought the mass
market PC graphics cards are quite capable (and relatively inexpensive in
large volumes) they have no practical use in this field of application.

One cheat is to use home theater chips.  There, too, there are compromises,
as none do anything much outside of 60Hz.

The DVI interface is currently limited to 165 million pixels per second.
This budget includes pixels allocated to blanking (H and V).  If you assume
1920 x 1080 with 15% H and 10% V blankings we get 189 million pixels per
second for 72fps.  Clearly outside the range of the current interface
specification.  At 1920 x 1200 (a common panel size) the number is 210M @
72fps.  There is a non-standard interface specification that will do
200Mp/s, but it won't do current HD-native panels at that rate.

The other aspect of "the interface won't support it" is that the LCD itself
has to be able to do the frame rate.  Ignore what you read in LCD monitor
sales sheets, they don't do 48 to 85Hz, at least not at the pixel level.
Pretty much all LCD monitors come with built-in scalers for both spatial and
temporal conformity with whatever is driving them.  So, while you may be
able to stuff an 85Hz signal into it, the pixel is actually driven at 60Hz.
Until LCD manufacturers make LCD's (DMD's, whatever) that can do the higher
frame rates, 72Hz will not be viable.  I don't think they have much in the
way of an incentive to go there.  That's the problem.

Martin Euredjian
eCinema Systems, Inc.
voice: 661-305-9320
fax: 661-775-4876
martin at ecinemasys.com
ecinema at ieee.org

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