Local Dimming On or Off During Calibration with BT.1886 - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 17 Old 04-09-2017, 10:22 AM - Thread Starter
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Local Dimming On or Off During Calibration with BT.1886

I wanted to gather everyone's opinions on this matter. I am always going back and forth on this and wanted some opinions and good reasonings. I have always been a FALD Off kind of person but BT.1886 accounts for black level which would not be accurate using FALD Off due to lighter blacks. So is it better to have it FALD on or off during calibration and if on, what would be the best way....APL or Window Size, ect. Thanks everyone!

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post #2 of 17 Old 04-09-2017, 01:50 PM
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Originally Posted by beardontwalk123 View Post
I wanted to gather everyone's opinions on this matter. I am always going back and forth on this and wanted some opinions and good reasonings. I have always been a FALD Off kind of person but BT.1886 accounts for black level which would not be accurate using FALD Off due to lighter blacks. So is it better to have it FALD on or off during calibration and if on, what would be the best way....APL or Window Size, ect. Thanks everyone!

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Yah I'm also curious about this as well. I'm still trying to calibrate to a point where I don't have crushed or grayish blacks

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post #3 of 17 Old 04-09-2017, 08:38 PM
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Originally Posted by beardontwalk123 View Post
I wanted to gather everyone's opinions on this matter. I am always going back and forth on this and wanted some opinions and good reasonings. I have always been a FALD Off kind of person but BT.1886 accounts for black level which would not be accurate using FALD Off due to lighter blacks. So is it better to have it FALD on or off during calibration and if on, what would be the best way....APL or Window Size, ect. Thanks everyone!
Personally, I would calibrate to BT.1886 with FALD Off for two reasons:
1. The TV is not capable of displaying the continuous gradation between its native black level and the "fake" black level with FALD On.
2. With FALD On, the BT.1886 curve becomes essentially gamma 2.4.

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Last edited by Dominic Chan; 04-09-2017 at 09:00 PM.
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post #4 of 17 Old 04-09-2017, 10:18 PM - Thread Starter
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Originally Posted by Dominic Chan View Post
Personally, I would calibrate to BT.1886 with FALD Off for two reasons:
1. The TV is not capable of displaying the continuous gradation between its native black level and the "fake" black level with FALD On.
2. With FALD On, the BT.1886 curve becomes essentially gamma 2.4.
It does produce 2.4 if windowed, I have heard plenty of reviewers say that they use 18% APL for everything because it gives a more realistic black level with content on screen (not as black as windowed and not as light as FALD Off). I do feel personally that off would be better (and easier) but I am so much of a perfectionist and want to make sure I am getting the most accuracy that I can. Could you go into more detail in regards to point #1 with the gradation. Thank you for your feedback!

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post #5 of 17 Old 04-10-2017, 03:36 AM
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Originally Posted by beardontwalk123 View Post
I wanted to gather everyone's opinions on this matter. I am always going back and forth on this and wanted some opinions and good reasonings. I have always been a FALD Off kind of person but BT.1886 accounts for black level which would not be accurate using FALD Off due to lighter blacks. So is it better to have it FALD on or off during calibration and if on, what would be the best way....APL or Window Size, ect. Thanks everyone!
You might well find that the best results are achieved by using a fake black level anyway.

As Dominic pointed out a BT.1886 gamma curve with a 0 nits reading follows a 2.4 power law profile.

Depending on the software you are using a fake (e.g. 0.03 or 0.05 nits) black level might perceptually produce the best results, which may differ from either local dimming on / off option.

As for the window size question, I find that this is very much display dependent. What TV do you have?

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post #6 of 17 Old 04-10-2017, 11:52 AM
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Originally Posted by beardontwalk123 View Post
Could you go into more detail in regards to point #1 with the gradation. Thank you for your feedback!
Here's an example:

If the white level of the TV is set to 100 nit, a 2.4 gamma would require 0.0015 nit at 1% grey, 0.0084 nit at 2% grey, 0.022 nit at 3% grey, etc. to show the gradation coming out of black (0.000 nit).

If the TV has a native contrast ratio of 10,000:1, the darkest black it can display without resorting to local dimming is 0.01 nit (100/10,000), meaning that it will not be able to display anything at 2% and below, resulting in a black crush.

You will avoid this issue if you calibrate with FALD off. Alternatively, you can "override" the black level in the calibration software, so that the target levels at 0, 1, 2, 3% grey will be 0.01, 0.023, 0.043, 0.086 instead, above the TV's black floor.

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post #7 of 17 Old 04-10-2017, 01:40 PM
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Originally Posted by Ips View Post
You might well find that the best results are achieved by using a fake black level anyway.

As Dominic pointed out a BT.1886 gamma curve with a 0 nits reading follows a 2.4 power law profile.

Depending on the software you are using a fake (e.g. 0.03 or 0.05 nits) black level might perceptually produce the best results, which may differ from either local dimming on / off option.

As for the window size question, I find that this is very much display dependent. What TV do you have?
When you say inputting a fake black level, can you tell me if this would done here in Calman?
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post #8 of 17 Old 04-10-2017, 02:38 PM - Thread Starter
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Quote:
Originally Posted by Ips View Post
You might well find that the best results are achieved by using a fake black level anyway.

As Dominic pointed out a BT.1886 gamma curve with a 0 nits reading follows a 2.4 power law profile.

Depending on the software you are using a fake (e.g. 0.03 or 0.05 nits) black level might perceptually produce the best results, which may differ from either local dimming on / off option.

As for the window size question, I find that this is very much display dependent. What TV do you have?
I have a Vizio P Series television. So if I have Local Dimming Off my black reading may be roughly .018. If I turn Local Dimming On and calibrate I could get a .004 or so black reading with APL patterns. What I am trying to figure out is which one would be more ideal with the BT.1886 curve.

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post #9 of 17 Old 04-10-2017, 02:53 PM - Thread Starter
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Originally Posted by Dominic Chan View Post
Here's an example:

If the white level of the TV is set to 100 nit, a 2.4 gamma would require 0.0015 nit at 1% grey, 0.0084 nit at 2% grey, 0.022 nit at 3% grey, etc. to show the gradation coming out of black (0.000 nit).

If the TV has a native contrast ratio of 10,000:1, the darkest black it can display without resorting to local dimming is 0.01 nit (100/10,000), meaning that it will not be able to display anything at 2% and below, resulting in a black crush.

You will avoid this issue if you calibrate with FALD off. Alternatively, you can "override" the black level in the calibration software, so that the target levels at 0, 1, 2, 3% grey will be 0.01, 0.023, 0.043, 0.086 instead, above the TV's black floor.
Ahhh, gotcha. That makes sense now. Would you want to calibrate a Local Dimming set like you would an OLED (or Plasma)? With the latter two the white would get a lot dimmer when more area was present on the screen but with Local Dimming the white gets a lot dimmer with less area on the screen. You would think you would want an APL of some sort to counter the effect or a smaller window size. Let's say with FALD Off the black is .018 and with it on and an APL pattern it reads .007, would the .007 better represent what we actually see and alter the curve that way?

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post #10 of 17 Old 04-10-2017, 08:45 PM
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When you say inputting a fake black level, can you tell me if this would done here in Calman?
Yes - enter a figure in the 'Black Level Target' option below the 'Use Measured Black Level' selection if you want to use an alternative figure with BT.1886 gamma in CalMAN.

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post #11 of 17 Old 04-10-2017, 08:46 PM
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Yes - enter a figure in the 'Black Level Target' option below the 'Use Measured Black Level' selection if you want to use an alternative figure with BT.1886 gamma in CalMAN.


Thank you very much.


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post #12 of 17 Old 04-12-2017, 12:18 AM
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I'm thinking about trying a Constant 10%APL after reading this white paper. http://www.spectracal.com/Documents/...20Patterns.pdf

My issue with Calibrating with No dimming is that Dolby Vision and HDR10 are meant to be calibrated with Local Dimming enabled as far as I know. That makes me think that Constant 10% APL should be used.

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post #13 of 17 Old 04-12-2017, 04:55 AM - Thread Starter
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I'm thinking about trying a Constant 10%APL after reading this white paper. http://www.spectracal.com/Documents/...20Patterns.pdf

My issue with Calibrating with No dimming is that Dolby Vision and HDR10 are meant to be calibrated with Local Dimming enabled as far as I know. That makes me think that Constant 10% APL should be used.
I have read that also, I am wondering why HDR Calibration doesn't use APL if that's the best appraoch. Also, on page 8 it talks about shutting Local Dimming Off to calibrate and measure gamma.....hmmmm.

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post #14 of 17 Old 04-12-2017, 05:13 AM
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Originally Posted by beardontwalk123 View Post
I have read that also, I am wondering why HDR Calibration doesn't use APL if that's the best appraoch. Also, on page 8 it talks about shutting Local Dimming Off to calibrate and measure gamma.....hmmmm.

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I just measured with constant apl on SDR and the differences are small. Some adjustments would be needed on the low end. For DV it really didn't do anything. What it boils down to IMO is that Vizio needs to stop doing global dimming. Utilize local dimming only.

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post #15 of 17 Old 04-12-2017, 05:36 AM - Thread Starter
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Originally Posted by shoman94 View Post
I just measured with constant apl on SDR and the differences are small. Some adjustments would be needed on the low end. For DV it really didn't do anything. What it boils down to IMO is that Vizio needs to stop doing global dimming. Utilize local dimming only.

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I think they do a global dimming to prevent blooming, otherwise there would be a ton of it. It's kind of a pick your poison, brighter picture with bloom or dimmer picture without (or much reduced). Black reading seems to have a way bigger impact on contrast ratio numbers than white readings do. That's good that 10% APL didn't change DV too much. I guess DV doesn't even take a black reading for the grayscale which is why you don't need ABL but with BT.1886 10% ABL would probably be appropriate for that black reading.

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post #16 of 17 Old 04-12-2017, 11:16 AM
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Originally Posted by beardontwalk123 View Post
I think they do a global dimming to prevent blooming, otherwise there would be a ton of it. It's kind of a pick your poison, brighter picture with bloom or dimmer picture without (or much reduced). Black reading seems to have a way bigger impact on contrast ratio numbers than white readings do. That's good that 10% APL didn't change DV too much. I guess DV doesn't even take a black reading for the grayscale which is why you don't need ABL but with BT.1886 10% ABL would probably be appropriate for that black reading.

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I think the blooming would be controlled just fine for real world​ content. IMO it unnecessary to also do global blooming. It hurts it's HDR performance.

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So calibrate with local dimming off then turn it back on in real watching? Or always leave off after calibration
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