Possible fix for burn-in - AVS Forum
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post #1 of 17 Old 01-03-2002, 06:12 PM - Thread Starter
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I have a Toshiba TN50X81 and have been using it for video games, letter boxed DVD's and HDTV OTA viewing. I don't have a problem with burn-in yet, but it occurred to me that it is similar to a problem older (Viticon) tube type video cameras had when focused on a stationary subject for some length of time. The way we would lessen the burn in image was to focus the camera on a well lit, white wall for several hours. I assume the phosphors of the camera tube would age and blend out the image burned in.

This got me to thinking that perhaps if a projection TV suffering from a letter box burn-in (black bars) were made to display an static image that was basically the reverse of the image that burned it in the first place, I.E., a letter boxed image with the center black and the bars pure white, that in some number of hours the difference in the two sections of the screen would be minimal. I would think that having the contrast turned up would accelerate the reverse burn in process so that it wouldn't take days to accomplish.

Ideally, the white bars of the image would transition to the black center section using a gray gradient so the registration of the image would not need to be so precisely aligned to the burned in image. Generating an image that would do as I described would be easy if you had a computer hooked up to your projection set as I do
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post #2 of 17 Old 01-05-2002, 04:22 PM
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Your theory is indeed correct. However burn in is an aging process of the screen phosphors. while you would lessen the noticeablity of the burn in you would also lessen the life and useable brightness availble on the screen in the process. CRTs offer the best reasonably priced picture at present, hopefully one day soon DLP or some new/exotic technology will make CRTs obsolete. How about scanning LASER diodes, just as a thought.
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post #3 of 17 Old 01-05-2002, 11:05 PM
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Yeah - scanning laser diodes - then we need
to worry about retinal burn in instead of
phosphore burn!
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post #4 of 17 Old 01-06-2002, 12:16 AM
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LOL, good one. Ever been to "Laserium" or "Eye see the light show", same principal except rasterized on a small flat screen instead of a planetarium dome.
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post #5 of 17 Old 01-06-2002, 12:55 PM
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Yeah - I have been to the DeAnza
planetarium (and the one near the
exploratorium) for some of those
laser/music light shows before.

Those systems aren't well suited for video
because:

1> As far as I know, combinations of lasers
(or lasers diodes) don't produce as complete
a color spectrum as current popular display
technologies (like CRT, LCD, DLP, etc.)

2> They use swiveling mirrors to scan the image.
I think those mirrors have to be too big for
them to consider scanning at the resolutions
and refresh rates we like
(e.g.: 800x600@85hz or 1280x768@72hz)
I think they use hard disk type "voice coils"
to move the mirrors around fast, but not
fast enough for good video playback.
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post #6 of 17 Old 01-06-2002, 01:34 PM
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Can you say laser printer? I knew you could. Raster imaging with lasers has the capabiity of extreme high resloution and adequate brightness at any credible image size. raster is accomlished with high speed rotating polygon mirrors and is a proven process. Enter a long lived blue laser diode and the system is reality, red and green laser diodes are off the shelf.

Let's see a 600 dpi laser printer can do about 5100 x 6600 on an 8.5 X 11 sheet of paper, scale that up and I see a display that would kick some butt.
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post #7 of 17 Old 01-06-2002, 02:23 PM - Thread Starter
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DTC mac,

Yes, the screen would age faster, but only in the black bar area and that's the whole point.

The black bar area is not as aged as the center section of the screen because it's not displaying any video information, and that's why the burn-in exists.

Aging the black bar area to the level of the center section by causing the screen to display white bars and a black center section would only result in the whole screen becoming equally aged.
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post #8 of 17 Old 01-06-2002, 02:31 PM
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yes guitarstar I agree, I was just stating that it is not a perfect solution as burn-in even if equalized lessens the service life of the CRT. Phosphors are not immortal so far as light output is concerened. Aged phosphors shift color somewhat and produce less and less light for a given e-beam intensity with age, eventually producing too washed out a picture to be satisfiying.
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post #9 of 17 Old 01-06-2002, 11:05 PM
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>>> Can you say laser printer?
>> Raster imaging with lasers has
>> the capabiity of extreme high resloution

I don't think it is fair to compare a printer
to a display device.

The printer is rated in pages per MINUTE
(lets say 10)

Whereas a live video display device typically
has something like 30 frames per SECOND.

So the live video device needs to be able to
rescan about 180 time more quickly than a laser
printer.

Moving the mirror(s) quickly enough _IS_ a real
problem. TI has somewhat solved this problem
with their DLP technology (micromirrors on a chip)
but it doesn't use laser technology.

U2 got some notoriety by spending huge bucks
to make a laser diode array giant screen for
their PopMart tour, but even with a "cost is no
object" design goal it still produced unrealistic
looking colors.

http://www.smartvision.com/press/press2.html
http://www.canoe.ca/MusicArtistsU2/apr24_u2.html
http://www.barco.com/corporate/en/pr....asp?index=214
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post #10 of 17 Old 01-07-2002, 12:28 PM
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Well if you dont like the idea dont buy one when they come out. BTW the slowness of a laser printer is in the data interface and image drum transfer not the raster engine.
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post #11 of 17 Old 01-08-2002, 02:05 AM
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I have noticed my CRT is shifting yellow in the aged center area. In order to correct the color shift, I would need to create a graphic in a paint program of bright blue in the bars with the rest of the area black. This would speed up the aging of the unaged bars area only on the blue CRT. Now, a whole screen is yellow, rather than true white. Next step would be to rebalance the color to pure white, ie increase the Blue CRT output in reference to the other CRT's.
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post #12 of 17 Old 01-08-2002, 08:40 AM
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Or better yet - buy a new CRT!

(sorry - I couldn't resist)
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post #13 of 17 Old 01-11-2002, 02:23 PM
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Any ideas on how long it would take "burn-in" an image? Let's use a video game or letter-box lines as an example. I'm sure their are many variables, but in general, what does it take?

Thanks.
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post #14 of 17 Old 01-11-2002, 02:27 PM
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PVR,
The U2 giant video screen was not made using scanning laser diodes as is being discussed. It was 'just' an LED array much like a gigantic marquee sign. Color fidelity wasn't good because they didn't use blue LED's in the mix. It still was quite spectacular for a rock concert.
Gary

Sorry for being OT, but the idea of scanning laser video projectors has always intrigued me.
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post #15 of 17 Old 01-11-2002, 03:16 PM
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Yeah - I know that it was a fixed array.

I thought it was still of interest in this post.

I still think they would have alot of trouble
moving a mirror fast enough to turn a laser
beam into a full frame-rate HDTV raster display.
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post #16 of 17 Old 01-11-2002, 07:24 PM - Thread Starter
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I guess this thread moved onto laser scan video......

You could easily cause a small mirror to oscillate fast enough to create a normal raster.

If hinged mirror was attached at a fixed point and the other end secured to an electromechanical actuator like a speaker driver, an oscillating signal could be applied to an actuator and the mirror would vibrate back and forth such that a laser could be directed at a screen. Additionally, there would need to be another actuator attached to tilt the mirror and create the raster. A scanning mirror suitable for use in a laser TV system seems very possible considering an average tweeter can respond to a signal of 20kHz, and TV's scan at 60Hz.
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post #17 of 17 Old 01-12-2002, 01:40 AM
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Beating a dead hoese here but as I said before the only practical stumbling block is the lack of long lived blue laser diodes. Frequency doubled IR diodes can produce blue but not at an appropriate output. Roughly speaking double freq. equals half the intensity. couple with the fact that the human eye is less sensitive to blue than red and green and you see the problem.
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