Setting brightness: by measurement or using pluge? - AVS Forum
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post #1 of 26 Old 10-13-2012, 04:12 AM - Thread Starter
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Both Chromapure and Calman recommend to use a black pluge pattern to set brightness. I have tried to do this, but I found this method erratic and in the end, I kept wondering if I had the right setting.
The point of having a meter is to calibrate by measurement.

So I wondered if I could do it by measurement. I tried the following on a Samsung 55ES8000 using a Display2. My Display2 is 2years old and might not be accurate, but the point I want to show is that I want to detect when there is a change in Luminance, and this the Display2 can do.
Following are the measurements as average of 5 readings, at IRE 0%, 1%, 2%, 3% and 4%. Brightness settings are 43, 44, 45, 46, 47 and 48. Luminance is in cd/m2.



My observations are:
At brightness setting 44 or lower, the luminance at 1% is the same as at 0%. Blacks are crushed so setting is too low.
At brightness setting 47 or higher, the minimum black level MLL at 0% starts to go up. As I want lowest MLL, this brightness setting is too high.

So my conclusion is that I have to set brightness at 45 or 46. In order to select between the two values, I would use a visual obervation of a pluge, or calculate gamma (with MLL offset).
Please note that making this graph took quite some time. But that was only done for this thread. For setting brightness in a calibration, all it needs are a few measurements at near black.

My questions are:
- is this a reasonable method?
- is it more reliable than a pluge method?
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post #2 of 26 Old 10-13-2012, 05:32 AM
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I would say not the best method. Keep in mind, regardless of instrumentation, your eye IS the final test. You can measure to your hearts content, but in the end, the result could be a very messed up picture. Brightness is part of a ratio for contrast and contrast varies depending on a number of factors. For this reason, your brightness level setting will vary depending on the amount of light in the room. A brightness setting set in a pitch black room will not be the same setting it should be set at when the lights are on. While going strictly by the numbers, you won't allow for this. One of the reasons for day and night settings. Vice versa, using PLUGE in a brightly lit room will result in a brightness level above that which would be desired for completely dark room. Really expensive colorimeter = $13,000. Eyeballs in their sockets working properly = priceless. smile.gif
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post #3 of 26 Old 10-13-2012, 06:33 AM
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I think in theory its a good way another way is to display a 100% black pattern, set brightness to its higest and then reduce it to the lightoutput dont drop any more.
however a real problem is that most meters are not 100% reliable with that little light, therefor a pluge pattern it still my prefered methode.
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post #4 of 26 Old 10-13-2012, 08:22 AM
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Also, some displays mute or reduce their output with a 100% black pattern, throwing a monkey wrench in this process unless you use some sort of pattern that has a bit of content away from the measurement area to keep the display "alive".
Pluge patterns aren't hard to interpret.
Suggestions, especially for when you are calibrating a night mode or whenever you want to make sure you are not raising the black floor at all: use a low APL pluge pattern in a very dark room, and walk right up to the display and get really close to it. You'll be able to see the threshold easier then.
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post #5 of 26 Old 10-13-2012, 08:50 AM
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Quote:
Originally Posted by Chad B View Post

Suggestions, especially for when you are calibrating a night mode or whenever you want to make sure you are not raising the black floor at all: use a low APL pluge pattern in a very dark room, and walk right up to the display and get really close to it. You'll be able to see the threshold easier then.

Is this setting also usable for normal, not bright sunshine daylight viewing?
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post #6 of 26 Old 10-13-2012, 09:00 AM
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Quote:
Originally Posted by visca blaugrana View Post

I think in theory its a good way another way is to display a 100% black pattern, set brightness to its higest and then reduce it to the lightoutput dont drop any more.
however a real problem is that most meters are not 100% reliable with that little light, therefor a pluge pattern it still my prefered methode.

Not to mention you may have to take 3 or 4 sets of readings down that low will take several minutes, versus the instant feedback from manually looking at it.

I think it will always be adjust with the pluge pattern, then possibly verify with a meter.

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post #7 of 26 Old 10-13-2012, 11:39 AM
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Ok, so then on a 0 ire pattern what do you want this too look like. At the point where there is no pixels firing or creating light not even the faintest. I have spots on my tv near the bottom that goes across where it looks like green pixles very very faint with the nose up to the screen that no matter where I set the black level of the tv it's a pn51d6500 the green pixles don't disappear. In the upper portion of the screen there is zero pixle activity at the point where the set doesn't get any darker if you continue lowering brightness any lower. What might be causing this? Could this be a uniformati issue? I have set all my panel voltage settings to factory sticker values.
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post #8 of 26 Old 10-14-2012, 02:12 AM
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The pattern that really works best is not a PLUGE patter, but a pattern with steps from 0-25 or so. If there is a square of gray for each 1% step, the results are VERY non-ambiguous.

Meters used for calibration are light meters... they measure light. And they suck at measuring dark. I have a $14,000 meter that is good down to maybe 3% white on panel displays. It will make readings below 3%... they just won't be meaningful/accurate. Averaging 3 inaccurate readings gives you an inaccurate average. There's no way an inexpensive meter is accurate at 4% let alone at steps below 4%.

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post #9 of 26 Old 10-14-2012, 08:52 AM
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Quote:
Originally Posted by Doug Blackburn View Post

The pattern that really works best is not a PLUGE patter, but a pattern with steps from 0-25 or so. If there is a square of gray for each 1% step, the results are VERY non-ambiguous.

Good examples are the Black Clipping pattern on the AVS (and now GCD) disk and the Advanced Brightness pattern on the Disney WOW BD, which uses 1% steps.

Just out of curiosity, what digital value does 1% stim correspond to?
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post #10 of 26 Old 10-15-2012, 11:27 AM
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^^ 235 divided by 100 = 2.35 digital increments per 1% step. Which is one reason you want to use a ditigal step pattern for the best resolution of whether you have the best Brightness setting

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post #11 of 26 Old 10-16-2012, 06:50 AM
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Quote:
Originally Posted by Doug Blackburn View Post

^^ 235 divided by 100 = 2.35 digital increments per 1% step. Which is one reason you want to use a ditigal step pattern for the best resolution of whether you have the best Brightness setting

Should the calculation be (235-16+1) steps / 100 = 2.2 digital increments per 1% step?
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post #12 of 26 Old 10-16-2012, 12:48 PM
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^^^ DuhOh - yes. I should have thought for 5 seconds more before clicking "send" tongue.gif

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post #13 of 26 Old 10-16-2012, 01:04 PM
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Quote:
Originally Posted by Doug Blackburn View Post

^^^ DuhOh - yes. I should have thought for 5 seconds more before clicking "send" tongue.gif

And to be very technically precise it is 2.19 bits per percent, you don't add the 1 back in. 220 levels but only 219 steps.

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post #14 of 26 Old 10-16-2012, 04:41 PM
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Quote:
Originally Posted by sotti View Post

And to be very technically precise it is 2.19 bits per percent, you don't add the 1 back in. 220 levels but only 219 steps.

so 1% gray is the equivalent of digital (2.19+16) 18.19?
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post #15 of 26 Old 10-16-2012, 05:05 PM
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Quote:
Originally Posted by PlasmaPZ80U View Post

so 1% gray is the equivalent of digital (2.19+16) 18.19?
Rounded down to 18.

You can see all the rounded bit levels in CalMAN.

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post #16 of 26 Old 11-15-2012, 08:09 PM - Thread Starter
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Quote:
Originally Posted by sotti View Post

Rounded down to 18.
You can see all the rounded bit levels in CalMAN.
Errors resulting from discrete bit levels.
If I take this a step further, and calculate e.g. 50% stimulus. Then this would be 16 + 0.5*219 = 16 + 109.5.
In bit level, then 16 + 109 or 16 + 110 has to be chosen, which is stimulus 49.7717% or 50.2283%.

How is this treated by calibration programs and calibration disc?

- Does a calibration program select one of the two levels and calculates gamma for that level? E.g it choses 16+110 and calculates gamma asuming the stimulus is 50.2283. Gamma is then calculated correctly.
Or does a program selects a bit level of 16+109 or 16+110 for the pattern, but calculates with a stimulus level of 50%. This would create an error in gamma.

- What happens if calibration patterns and programs form different sources are mixed?
E.g. a calibration disc from one source which uses a bit level of 16+109, and a calibration program which assumes the pattern is 16+110. That would introduce a gamma error of 0.05 which a calibrator sees as a perceived deviation even if it is not there.

Just some basic questions. Am I seeing things wrong? Can someone explain.
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post #17 of 26 Old 11-15-2012, 08:40 PM
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CalMAN uses the built-in round function for .net which is an http://grouper.ieee.org/groups/754/ standard for rounding.

So 50% rounds up to 126.

CalMAN calculates all it's values off of the discrete 8bit values.

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post #18 of 26 Old 11-20-2012, 05:36 AM
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On modern displays, assuming you don't have a display which is doing any kind of adjustment with a full black field (which is quite an assumption to make now) you should be able to set it in about five seconds with the brightness control.

When you turn down the brightness, there will be a point at which black stops getting any darker, and any upwards adjustment raises the black level. Congratulations, you now have brightness set correctly.

Even if the panel clips the lower 1-2% you're still better off with the display set to give you the darkest black level it can do, because today's display contrast is so low.
Even the Kuros lose all black level advantage if you set them using a brightness pattern rather than setting brightness at the point where the panel turns its darkest.
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post #19 of 26 Old 11-20-2012, 08:09 AM
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I think I read this somewhere, on a blu-ray or something, sometimes they "fade to black" in between scenes. Pauze at the darkest piont, then turn down brightness untill it doesnt get any darker, done.

Or, on this "fade to black "pattern"", turn down brightness completely, then turn up 1 click at a time untill the screen gets brighter, then one click down again, done.
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post #20 of 26 Old 11-20-2012, 05:33 PM - Thread Starter
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Quote:
Originally Posted by Chronoptimist View Post

On modern displays, assuming you don't have a display which is doing any kind of adjustment with a full black field (which is quite an assumption to make now) you should be able to set it in about five seconds with the brightness control.
When you turn down the brightness, there will be a point at which black stops getting any darker, and any upwards adjustment raises the black level. Congratulations, you now have brightness set correctly.
Even if the panel clips the lower 1-2% you're still better off with the display set to give you the darkest black level it can do, because today's display contrast is so low.
Even the Kuros lose all black level advantage if you set them using a brightness pattern rather than setting brightness at the point where the panel turns its darkest.
Exactly, that is the point I wanted to make with my original post.
In my case on the Samsung 55ES8000, avoid dimming by using movie mode or large APL pattern, display black, measure and set brightness from a higher to a lower setting. At brightness setting 46, black level stops geting darker. Mission accomplished. Easier than using pluge.
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post #21 of 26 Old 11-21-2012, 02:58 PM
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Quote:
Originally Posted by Wouter73 View Post

I think I read this somewhere, on a blu-ray or something, sometimes they "fade to black" in between scenes. Pauze at the darkest piont, then turn down brightness untill it doesnt get any darker, done.
Or, on this "fade to black "pattern"", turn down brightness completely, then turn up 1 click at a time untill the screen gets brighter, then one click down again, done.
There is nothing to guarantee that a "fade to black" is actually properly fading to black. You should use test patterns for this.
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Originally Posted by turboman123 View Post

Exactly, that is the point I wanted to make with my original post.
In my case on the Samsung 55ES8000, avoid dimming by using movie mode or large APL pattern, display black, measure and set brightness from a higher to a lower setting. At brightness setting 46, black level stops geting darker. Mission accomplished. Easier than using pluge.
http://www.avsforum.com/content/type/61/id/76970/width/500/height/1000
Yes, as long as you are sure that you are able to avoid dimming etc. this is the easiest way to set brightness correctly.
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post #22 of 26 Old 11-22-2012, 12:11 AM
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I believe there are 0% white patterns on the cgd smile.gif
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post #23 of 26 Old 11-22-2012, 10:00 AM
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One caution for DLP RPs in general. If there is any menu OSD the measured light level will usually continue to decrease all the way down to a brightness setting of 0. You'll need to exit the menu after each settings change.

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post #24 of 26 Old 11-22-2012, 10:13 AM
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OK, perhaps im doing something wrong here.
I have a 55VT30 - setting the correct brightness using the AVSHD disk means my gamma is stuck at about 2.13 - increasing it to 2.2 crushes blacks confused.gif

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post #25 of 26 Old 11-23-2012, 12:32 PM
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Gamma won't "crush blacks" all by itself... something else has to be changing or the "new" gamma setting isn't proper/linear/uniform. Measurements would probably show a change in response in darker steps that explains what is going wrong with the darker gamma setting. Just because the TV has a gamma control doesn't mean the control does what it is supposed to do... nor does the presence of a control mean you get the real gamma value that the control is labeled for (in other words, setting the control to 2.2 doesn't mean that's the ACTUAL display gamma, nor does it mean you get 2.2 at every grayscale step... you might measure 2.5 at dark steps, 2.3 in some gray steps, 2.2 at 60%, and 1.9 from 80%-100%... you just never know what you are getting with different gamma settings when you don't have a meter to see what's really happening at each setting.

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post #26 of 26 Old 11-23-2012, 01:42 PM
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Quote:
Originally Posted by Doug Blackburn View Post

Gamma won't "crush blacks" all by itself... something else has to be changing or the "new" gamma setting isn't proper/linear/uniform. Measurements would probably show a change in response in darker steps that explains what is going wrong with the darker gamma setting. Just because the TV has a gamma control doesn't mean the control does what it is supposed to do... nor does the presence of a control mean you get the real gamma value that the control is labeled for (in other words, setting the control to 2.2 doesn't mean that's the ACTUAL display gamma, nor does it mean you get 2.2 at every grayscale step... you might measure 2.5 at dark steps, 2.3 in some gray steps, 2.2 at 60%, and 1.9 from 80%-100%... you just never know what you are getting with different gamma settings when you don't have a meter to see what's really happening at each setting.

I am using a metre. Perhaps its the pattern type I'm using - perhaps it's because im still learning this set which is much more of a challenge than my previous sammy???

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