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Author Topic: TFT Display  (Read 1234 times)

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Sam66

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TFT Display
« on: August 16, 2002, 12:23:26 pm »
Ok, I'm new to all this so please don't flame me if this is a silly question but:

Other than cost, authenticity and maybe viewing angles, is there any reason a TFT display shouldn't be used for a mame cabinet (I'm thinking slimline cocktail cabinet).

Any response, positive or negative will be appreciated.

Sam66

MameFan

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Re:TFT Display
« Reply #1 on: August 16, 2002, 02:13:41 pm »
2 Words: Horrendous Scaling!


LCD monitors are great for a FIXED resolution and refresh rate.  As soon as you start playing around with displaying different display sizes, it forces the monitor to scale your picture to fit the FIXED dot layout it has.

Cheap old LCD's wouldn't even do that... they left you with a huge black border.

New ones will scale, but will cause 2 artifacts:
1) Blocky, uneveness
2) Fuzziness.

It all depends on the mfg, how much electronics is in the monitor, etc..


The problem is, for example, most "classic" games are in the range of 320 x 240 pixels.  If that were the case, then it would scale to 640x480 nicely (4 pixels for every 1), or even 960x720 (9 pixels for every 1). [Worse though not all use that.. it might be 328 x 244 pixels, making multipliers not work as well]

Problem is, it gets hard (or impossible) to tell the monitor when you want it to scale (fill in with average dots) and when you want it to leave a border.

Therefore the resulting picture will have some pixels doubled, some tripled, causing things to be out of proportion to each other. Or it will fill in these areas with dithering (pixels of an average color between 2 adjacent pixels).

Think of taking a game screen and running it thru a JPEG compression at say 90% compression.. Thats what it will look like on some LCD's.  Or it will fill a tiny portion of the screen.

CRT (tube) technology has the ability to vary the spacing between each pixel that an LCD doesn't. An LCD has it's dots at precisce positions and cannot move at all. You must use or not use every dot on the display, and not be able to have them fill in like a CRT does so nicely since it uses Analog technology.


In addition, for the most part, trying to run with fake scan lines turned on looks horrible on LCD.

Until LCD's can pack 4 times as many dot points into the same space they do now, LCD is not a viable option for a "quality" display in a cabinet.   Yeah, it's fine for playing Mame on your notebook on the sofa with the keyboard, but not to have the real experience.

Sam66

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Re:TFT Display
« Reply #2 on: August 19, 2002, 05:00:27 am »
Thanks for taking the time to reply.  Looks like I'm just going to have to search around for a nice short neck monitor.

MameFan

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Re:TFT Display
« Reply #3 on: August 19, 2002, 10:19:34 am »
One thing I forgot: Refresh times of the pixel. (Not of the screen--that's fixed at 60 or 70 hz on most LCD's)

Each LCD pixel takes a certain amount of time to "turn on" and "turn off".  Since LCD is made up of liquid crystals, when electricity is supplied, it takes time for the crystal to rotate 90 degrees to let thru or not let thru light. This is called "Rise/Fall" time.

The wost LCD's out right now are about 50ns.  It takes about 25 ns to turn on, and 25 to turn off.   THe best ones are around 25ns.. 15 ns to turn on, and 10 to turn off.

This may not affect Mame emulated games too much, but something to consider. I know a lot of gamers playing the latest hot PC games dont like LCD due to this.  I causes smearing and other artifacts since the display dots dont keep up with the speed the video card is supplying the picture.

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Re:TFT Display
« Reply #4 on: August 19, 2002, 10:56:34 am »
I knew about the slow response on older TFT displays.  I've seen a few reports that the newer 25ms response times are fine for most games.  That, along with the increased brightness and better viewing angles of new screens is what made me consider TFT.  I didn't think about the rescaling problem though : (