Bt.1886 and local dimming - AVS Forum
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post #1 of 19 Old 02-21-2013, 05:08 AM - Thread Starter
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Is it advisable to turn off local dimming if calibrating to bt.1886? Even if local dimming will be used when viewing material to improve black level on a LED panel.
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post #2 of 19 Old 02-21-2013, 08:09 AM
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Greetings

It messes up the test patterns so turn them off. Test patterns don't exactly represent real life material hence a test pattern.

Local dimming is like auto iris in a way ... not right or wrong ... but there to compensate for an inherent technology weakness. It had positives and negatives.

Turn it back on when you are done ... or not.

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post #3 of 19 Old 02-21-2013, 08:47 AM - Thread Starter
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Thanks
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post #4 of 19 Old 02-22-2013, 11:04 AM
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You want all the other "Auto" or "Dynamic" things turned off also as they can also alter the images in unwanted ways, even during calibration with simple patterns being displayed... but you don't want to turn any of those things back on after calibration. Some mid-to-high-end TV models have a room light sensor that changes the images in response to how much light is in the room... that should be off also.

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post #5 of 19 Old 02-22-2013, 11:49 AM - Thread Starter
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Problem is night time watching of an edge lit led set is unbearable without local dimming on. Even with bias lighting.

The reason I asked the question is that local dimming on or off has a dramatic effect on black level which obviously has a major impact on gamma targets when calibrating to Bt.1886.

I have calibrated the panel with local dimming off then measured with local dimming on. It does have fairly big impact on gamma at 10,20 & 30 IRE and does cause a little gamma hump at 90. White balance does shift a little but we are only talking a minuscule difference.

Just for reference I am using I1 display 3 profiled to I1pro.
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post #6 of 19 Old 02-22-2013, 12:32 PM
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Quote:
Originally Posted by Skood View Post

The reason I asked the question is that local dimming on or off has a dramatic effect on black level which obviously has a major impact on gamma targets when calibrating to Bt.1886.

Edge lit doesn't really have local dimming, just dynamic dimming, you need to have back lit LED to do local dimming.

Bt.1886 primarily is factoring in the contrast ratio between black and white into it's formula, (although the absolute numbers to matter a bit). So calibrate with the dimming off, then you can turn it back on.

While it's on, you'll never be able to get meaningful information about what your gamma is doing.

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post #7 of 19 Old 02-22-2013, 01:54 PM
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Greetings

Actually .... smile.gif MArketing marketing ... they have added a local dimming feature to the edge lit too. It kicks on for w/s films ... making the black bars darker than before. No it is not as good a local dimming with backlit LED zones ... but it is better than nothing and they are calling it local dimming.

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post #8 of 19 Old 06-04-2013, 10:08 PM
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Quote:
Originally Posted by sotti View Post

Edge lit doesn't really have local dimming, just dynamic dimming, you need to have back lit LED to do local dimming.

Bt.1886 primarily is factoring in the contrast ratio between black and white into it's formula, (although the absolute numbers to matter a bit). So calibrate with the dimming off, then you can turn it back on.

While it's on, you'll never be able to get meaningful information about what your gamma is doing.

I take it, the best thing to do is calibrate with 709, and 1886 and see which results you prefer.
Currently do 709/2.22 with Local Dimming ON. Should Local Dimming be On for 709, and OFF for 1886?
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post #9 of 19 Old 06-06-2013, 12:51 AM
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Originally Posted by sotti View Post

Edge lit doesn't really have local dimming, just dynamic dimming, you need to have back lit LED to do local dimming.

Actually some have LD and not only global or dynamic dimming
But they have only 16 to 32 zones (depending on manufacturer and model) which are quite large (from the edge to the middle of the screen).
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post #10 of 19 Old 06-06-2013, 04:14 AM
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Originally Posted by p5browne View Post

I take it, the best thing to do is calibrate with 709, and 1886 and see which results you prefer.
Currently do 709/2.22 with Local Dimming ON. Should Local Dimming be On for 709, and OFF for 1886?
I second this question. I read this thread before and was under the impression that LD should be turned off while calibrating either a target display gamma or bt.1886 gamma. While under this impression I recently calibrated my LH90 with LD off, to a display gamma of ~2.35.
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post #11 of 19 Old 06-06-2013, 05:24 AM
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Originally Posted by rahzel View Post

I second this question. I read this thread before and was under the impression that LD should be turned off while calibrating either a target display gamma or bt.1886 gamma. While under this impression I recently calibrated my LH90 with LD off, to a display gamma of ~2.35.

I think it depends upon the set and you have to experiment to see if having LD on or off effects the results. I have a Sharp elite 70x5 along with a Lumagen Radiance. Have calibrated the set ~ 12 times since September, 2011. Started with LD off and after a few tries with that compared gamma/grayscale results to measures with LD on. No difference in any of the results. Finally, since I watch the set with Intelligent Variable Contrast (IVC) on the low setting, I measured the results with IVC Low on. Again, no difference in gamma or grayscale results although IVC Low increases 100% FL to 48-49 vs. ~ 32 for LD on. Most resent calibrations have been with IVC Low on during the entire process. Note that I don't calibrate to a 1886 target. Rather, I start with ~ 2.17 at 5% rising to 2.3 at 20% with that remaining constant to 80% and raise that to ~ 2.45 at 95%. The raise at the end provides more detail in bright clouds etc.
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post #12 of 19 Old 06-06-2013, 02:41 PM
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You can't calibrate the TV with any dimming or auto feature turned on while you are actually calibrating. After you are done calibrating... local or global dimming is often useful/helpful and there is no harm in turning it back on... but it will mess up your calibration if you do not turn it off before you calibrate.

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post #13 of 19 Old 06-06-2013, 03:55 PM
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Quote:
Originally Posted by Doug Blackburn View Post

You can't calibrate the TV with any dimming or auto feature turned on while you are actually calibrating. After you are done calibrating... local or global dimming is often useful/helpful and there is no harm in turning it back on... but it will mess up your calibration if you do not turn it off before you calibrate.

what if you use full fields?
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post #14 of 19 Old 06-06-2013, 04:22 PM
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Originally Posted by PlasmaPZ80U View Post

what if you use full fields?
Was just about to ask the same thing. This seemed to be the preferred method back a year or so ago when I first calibrated my LH90... to use full-field patterns with LD on.
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post #15 of 19 Old 06-07-2013, 05:20 AM
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Originally Posted by Doug Blackburn View Post

You can't calibrate the TV with any dimming or auto feature turned on while you are actually calibrating. After you are done calibrating... local or global dimming is often useful/helpful and there is no harm in turning it back on... but it will mess up your calibration if you do not turn it off before you calibrate.

Doug: I am only reporting the results I obtained. I started by turning LD off as well as every other "enhancement". Someone on another site showed an ugly graphic supposedly showing how turning LD on after calibration screwed up gamma. In an effort to replicate that, I measured gamma/greyscale after LD was turned on. Results were identical to LD off results and gamut DEs were identical . Guess is person on other site forgot to reset 100% point in doing his comparison or just wanted to throw mud at Elite. From there I progressed to calibrating with LD on and going back afterward to compare results with LD off. Again no difference. Since I watch with IVC Low on, I tried a calibration with it on and compared to LD on and LD off. No appreciable differences. I currently use the IVC low results for viewing. Where I may differ in my approach from others is that all these calibrations were done manually with an older version of Chromapure and a Chroma 5 Pro meter. I used the Radiance standard windows to start because I had always used those with my previous plasma calibrations. I continue to use the windows patterns. As a guess, perhaps the Elite's LD processing doesn't activate with test patterns other than to increase luminance when IVC is activated.
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post #16 of 19 Old 06-07-2013, 07:14 PM
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From what I'm seeing, after setting the Gamma to the BT1886 for calibrating, this has brought out the best I've ever seen my 2 LG 55LHXs - they are just Beautiful and very Natural looking. I always though it was a TV just waiting for the Meters and Software to catch up to them. I doubt very seriously, I can make them look any better! I'm finally more than happy with the results!
(Notice, I did not say `They POP!')
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post #17 of 19 Old 06-08-2013, 04:50 PM
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If you use full fields with local dimming turned on, you will get whacky gamma results because the TV will dim for the darker grayscale steps and brighten for the brighter grayscale steps in spite of using full fields. Using full fields does not stop the TV from "gain riding" the luminance changes in full-field patterns. Local dimming will dim small areas, but it is not limited to darkening or brightening small areas. It will darken or lighten the entire image area if you use full frames... depending on how close to white or black the full field pattern is. In fact, one of the issues with calibrating plasma displays is that they have brightness limiting that kicks-in when images get increasingly bright. You can't stop it from happening. In LCD displays, if you leave dimming on, you essentially turn them into a plasma TV with essentially the same issue to deal with. If you turn dimming off, you then have 1 specific black level and 1 specific white level and you can then build your gamma curve between those 2 points so gamma is accurate.

Now this is the part that trips-up a lot of people. Let's say you turn dimming off to calibrate an LCD TV. And let's also say you are able to get a nice 2.25 gamma all the way through the grayscale. OK... now lets say you are viewing Picture-In-Picture and you have a hockey game in the large main screen (bright white images most of the time) and let's say you have a darker movie running in the PIP window. So with dimming turned on, the image will want to be at maximum brightness for the hockey game because of all the "white" ice. But because you calibrated with dimming off, the hockey game images will be calibrated to the 2.25 gamma standard (we'll it's my standard, not official, but it should be the standard for gamma setting) . The whole image might be brighter than an average image (if your TV's dimming works that way), but it will still measure pretty close to 2.25... it won't be exactly 2.25 Gamma, but it's likely to be pretty close. Now the dark movie in the small window... that also will be close to 2.25 gamma because when you dim, you reduce luminance, but you maintain the same luminance relationship between grayscale steps and you'll still have pretty close to 2.25 gamma within the darker PIP images. So if you calibrate with dimming off, you get reasonably similar gamma with fully bright images or fully darkened images.

But if you leave local dimming on during calibration, you get a wrong (errors) gamma all the time no matter whether the TV images are dark or light or medium, average luminance. The bright hockey game's gamma will be wrong, and the dark PIP image will also have a bad gamma.

So my advice is to ALWAYS turn off auto dimming, local or full screen, for calibration to get the best looking images. Once calibration is done, most people will probably find gamma looks fine with dimming turned on and that the dimming really helps to improve black level noticeably.
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post #18 of 19 Old 06-08-2013, 05:39 PM
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Yes, I read to do Gamma BT1886 calibrations with LD Off.
Turn back on when finished, elsewise the Milky Blacks are quite the distraction (Also PIPs - so I don't do any of those either.)

Big Mistake - now leave LD On!
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post #19 of 19 Old 06-08-2013, 06:35 PM
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Thanks Doug. Very helpful post as usual.
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