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I've seen some projector specs specify TV lines. Quite a few projectors (NEC LT156, for example) have about 550 TV lines. The NEC LT156 says it supports 720p. How can it do that with 550 TV lines? The Panasonic 711XU has 760 TV lines. It seems like supporting 720p is easy for the 711XU.


The bottom line is: What does the TV lines spec mean? Are more really better?


Thanks for the help in understanding this spec.

Honcho


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Honcho
 

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Hi,


Guy Kuo would explain better. However, the below is along the lines of what Guy Kuo, who helped make the AVIA DVD, has said in the past.


The TVL measurement is the maximum number of vertical lines you can squeeze in the biggest possible perfect circle centered in the middle of your display.


The DVD 720x480 standard in 4:3 allows you to squeeze 540 horizontal pixels inside a circle centered in the middle of the 4:3. That translates to a max of 540 TVL. Now, in 16:9, the TVL rating is actually lower because the circle is smaller -- only 405 TVL! What gives -- anamorphic DVD has lower TVL than nonanamorphic DVD? Many people argue that TVL is really an obsolete analog resolution measurement standard that shouldn't be used with things like digital projectors.


The TVL measurement was invented in the analog days.


The TVL measurement is a horizontal resolution measurement NOT vertical resolution (a frequent confusion)


The TVL measurement has nothing to do with scanlines (a frequent confusion)


The TVL measurement really should be obsolete in today's digital world.


Moral -- Pay more attention to the digital projector's panel resolution instead. (And the quality of its internal scaler, if applicable).
 

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Here's the bottom line:


Vertical resolution is ALWAYS 480 interlaced for NTSC.


Total lines refers to horizontal resolution but it is still referenced to the vertical resolution and thus doesn't include the 4:3 scaling factor. Thus horizontal pixels is total lines X 4 / 3. So 540 lines equals 720 total pixels which is the resolution of DVD.


The term TVL should be tossed away as quickly as possible.


-Mr. Wigggles
 
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