Samsung Cell Light Control - Explained by a Samsung insider - AVS Forum
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post #1 of 75 Old 04-07-2014, 11:27 AM - Thread Starter
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This information comes straight from a Samsung insider. It is not something I made up. Don't argue with me, I'm just relaying what the insider told me. This information is current as of today, April 7, 2014.

The Cell Light control determines the point where automatic brightness limiting kicks-in. At the highest setting. ABL kicks in at the highest level available... typically somewhere around 60%. At the lowest Cell Light setting, ABL begins much lower, in the range of 30% white.

Since most people already don't like ABL, it is counterproductive to use any Cell Light setting below 20 (or 10 on earlier plasma models with this control).

How to tell if and when automatic brightness limiting is being applied (requires a meter to measure):
Display full-screen gray patterns. Start at 0 and go all the way to 100% white. With Cell Light set to 20, the gamma curve should look normal up to 60% or close to that, while higher %white levels will tend to "level off". Set Cell Light to a lower setting, say 5 or something like that, and run the full-screen patterns again. Now you should see that when you are somewhere close to 30%, the pattens don't get as bright. So... with Cell Light at 20, you might get 17 or 18 fL for 100% white (depends on Contrast setting) while Cell Light being set to 5 or some other low number would limit 100% white even more making midtones (40%-60%) AND highlights dimmer than you'd like them to be.

Samsung plasmas with Cell Light... the Contrast control is still the control to use to set the white level (using a small window pattern, not a full-screen pattern) and it may still cause white to clip if set too high, So you still need to use a test pattern that shows, say, 220-255 so you can find the highest Contrast setting you can use without clipping white. That is not necessarily the BEST Contrast setting, it is just the HIGHEST setting you can use without clipping white. You may find that 95 is where white begins to clip, but you might find that "80" produces 33 fL which is around where you want to be if the room is very dark.

Bottom line... if you want MORE brightness lmiting, use Cell Light settings below 20. If you want LESS brightness limiting, set Cell Light to the highest setting, leave it there, and forget it exists.

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post #2 of 75 Old 04-07-2014, 02:36 PM
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Thanks for that...I've played with the Cell Light and could not determine exactly what it was doing.
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post #3 of 75 Old 04-07-2014, 02:37 PM
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this seems really backwards.

if ABL is about power limitations, then adjusting cell light shouldn't affect ABL.

either way, I have my f8500 set to 10(out of 20) and notice zero ABL behaviour, so I'm sticking with it, cause 20 burns my retinas tongue.gif

and I hope you don't take this as arguing, I'm really inquiring as my knowledge has been more inferred than expressed.

regarding contrast, I also thought you wanted to adjust contrast to the highest setting that avoiding white clipping. and then used cell light(or backlight on an lcd) to achieve the desired brightness of the display.
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post #4 of 75 Old 04-08-2014, 08:52 PM
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Doug,

Thanks for chiming in. Glad to finally know the true function/implementation of Cell Light. It's been confusing since so many noted calibrators have advocated lowering Cell Light to control light output- primarily in regards to the F8500.
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post #5 of 75 Old 04-08-2014, 10:22 PM
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Quote:
Originally Posted by DarkHorse88 View Post

Doug,

Thanks for chiming in. Glad to finally know the true function/implementation of Cell Light. It's been confusing since so many noted calibrators have advocated lowering Cell Light to control light output- primarily in regards to the F8500.
its has been noted because that is how you calibrate the 2013 Samsung plasmas (and some of their LCDs) in conjunction with the 10 point grayscale controls. Per Engineering Korea, if you use a Contrast setting that is not equal to 95, the 10 point controls will NOT line up properly with their respective targeted adjustment points. I'm not sure who this Samsung insider is, but I recommend they speak to Engineering in either Korea or NA to get a full explanation of what I've posted. Everyone else can simply try it.or not.
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post #6 of 75 Old 04-09-2014, 04:39 AM
 
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With my very limited skills and equipment it was impossible to get things to calibrate correctly for 38-40fL at 20 cell on the F8500. I was one of the first to get the TV and proclaimed this many times on this forum (with a lot of backlash may I add wink.gif ).

Simply put, cell 20 and contrast at any level for a lower fL would not calibrate and looked 'off' no matter how I tried to balance the rest of the TV.

Thanks for the engineer Korea info D-Nice, I had landed on 95 contrast without that info through trial and error smile.gif
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post #7 of 75 Old 04-09-2014, 05:06 AM
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Quote:
Originally Posted by D-Nice View Post

its has been noted because that is how you calibrate the 2013 Samsung plasmas (and some of their LCDs) in conjunction with the 10 point grayscale controls. Per Engineering Korea, if you use a Contrast setting that is not equal to 95, the 10 point controls will NOT line up properly with their respective targeted adjustment points. I'm not sure who this Samsung insider is, but I recommend they speak to Engineering in either Korea or NA to get a full explanation of what I've posted. Everyone else can simply try it.or not.
So apparently you can't adjust the brightness output and minimize ABL while at the same time getting the 10 point white balance controls to line up. Or, are you also claiming that cell light doesn't affect ABL, and is a true brightness control like LCD backlight?
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post #8 of 75 Old 04-09-2014, 05:16 AM
 
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^ As I understand it (please correct me if I am wrong):

I believe it is a trade-off as 20 cell goes far beyond older plasma TVs luminance levels, no lower contrast setting can compensate to achieve a good reference 35-40fL output.
ABL would be more aggressive at lower cell but in the grand scheme of things it is the lesser of all evils.
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post #9 of 75 Old 04-09-2014, 06:43 AM
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I noted the connection between ABL and Cell setting almost 2 years ago. But, the F8500 presents a problem because 20/95 is often too bright so you have to lower cell if you also want good alignment of the 10 pt controls.
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post #10 of 75 Old 04-09-2014, 09:38 AM - Thread Starter
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So what is the problem with lowering Contrast to where it needs to be to get the white level you want (circa 35 fL for a dark room, for example) while leaving Cell Light at 20 and make few passes of grayscale to find the points that the 10 point controls are adjusting and doing the calibration correctly with the minimum amount of ABL to deal with?

It appears there are 2 options... doing the above, or reducing Cell Light, leaving Contrast at 95 and causing brightness limiting to begin at a lower point in the grayscale. (for this one TV model where the 10 point controls are thrown off by Contrast, for other models where that doesn't happen, obviously the highest Cell Light setting is the only RIGHT Cell Light setting unless you enjoy brightness limiting.

Seems to me that the first option is the best option, especially for those who enjoy hockey or skiing.

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post #11 of 75 Old 04-09-2014, 09:43 AM
 
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I could not reach 35fL with cell at 20 no matter what I set contrast or 10 point to.
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post #12 of 75 Old 04-09-2014, 09:54 AM
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Exactly how far out of alignment do the 10 point adjustments get? And, what exactly does out of alignment mean? Are they not evenly spaced?
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post #13 of 75 Old 04-09-2014, 10:01 AM
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Calibrated Brightness and Contrast for the Best results with Cell at 15. Dynamic Range Calman Workflo had me set the B&C at 45 and 85 for the Optimum Results. Autocaled the 21 and 125 Point. B&C now off. Recalibrate, and the Optimum was now 46 and 80, which throws off the 21 and 125. Recalibrate again, and now the Optimum is now 45 and 72.
At this point, reset brightness to 45, and Contrast to 85, and did the AutoCals and said the heck with the B&C. Maybe with the Cell at 20, this problem will disappear?
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post #14 of 75 Old 04-09-2014, 10:19 AM - Thread Starter
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Quote:
Originally Posted by fierce_gt View Post

this seems really backwards..

No it doesn't. There is no backwards or forwards. The control does what the engineers made it do. If they wanted the control to make pinwheel images, it would make pinwheel images. You cannot infer ANYTHING about what the control does from the name of the control. The Contrast control does not control Contrast (it can change contrast ratio, but the average person doesn't think in those terms). The Brightness control does not affect brightness. The Sharpness control rarely affects real image sharpness (most Sharpness controls do nothing at their "off" setting and add edge artifacts above their "off" setting). And on and on and on.
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if ABL is about power limitations, then adjusting cell light shouldn't affect ABL..

There are both power and heat issues with plasma... the brighter they run, the more they act like space heaters. Heat damages phosphors so you don't want to "burn" your screen by friving it too hot. The power supply required to produce full-screen 100% white at, say 55 fL for daytime viewing would be much larger and use much more power than power supplies in typical plasma TVs. For a while there, plasma TVs were using so much energy that some areas were considering "banning" plasma TVs because of their inefficiency. So power consumption (and heat) are serious issues for plasma displays. If you want efficiency and low heat output, set Cell Light lower and live with the more severe ABL. If you want the best possible images, leave Cell Light at the highest setting, reduce Contrast to control white level (which is what the Contrast control does). Or do a combination... when your viewing is non-critical, use a low Cell Light setting... when you want the best images, crank Cell Light up and bring Contrast down so you aren't frying your eyeballs.
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either way, I have my f8500 set to 10(out of 20) and notice zero ABL behaviour, so I'm sticking with it, cause 20 burns my retinas tongue.gif .

The issue with ABL is that without any Cell Light control (every other plasma TV manufactured except Samsung models), ABL kicks in around 60% white and the TV, if you send full-screen patterns, just doesn't get a whole lot lighter when you send full screen patterns above 60%. Anyone who enjoys hockey or skiing or Lawrence of Arabia will see ABL. In fact, if you use a full screen white pattern, you will measure around 17 fL for 100% white while changing to a window pattern where the 100% white area occupies about 10% of the screen area with the rest of the screen is black will measure around 32-35 fL depending on brand/model. So the full-screen white is close to half as bright as just a small area of white. This robs dynamic range from images and knocks your contrast ratio WAY WAY down when you are viewing content with a lot of highlight area in the image. If you aren't calibrating the TV, there is no rule that says you have to leave contrast at 95. So with a low Cell Light setting, you might get 0-12 fL for full-screen window patterns (0-100%) while the highest Cell Light setting might produce 0-17 fL for full-screen 100% white. Will you see an effect on a 10%-of-screen-area window pattern with different Cell Light settings? Not sure, never bothered to check... could be. Early versions of Cell Light caused an S shaped gamma curve, Samsung has tuned-out most of that over the years, but SOMETHING will show up with the right
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and I hope you don't take this as arguing, I'm really inquiring as my knowledge has been more inferred than expressed. .

Nope. I just see someone who doesn't have enough information yet to be making good settings choices.
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regarding contrast, I also thought you wanted to adjust contrast to the highest setting that avoiding white clipping. and then used cell light(or backlight on an lcd) to achieve the desired brightness of the display.

This is completely wrong, but I fully understand how you got to that point-and it's not your fault AT ALL. Every test/setup disc and thousands and thousands of people repeat this baloney until everyone assumes it must be true. It is NOT true, especially now. It used to be true most of the time when the only video displays available were CRTs and raising the Contrast control just a little too much would either clip white or cause blooming (destroys detail) or both so for CRTs the best Contrast setting was almost always the highest setting you could use that did not clip white or cause blooming (or that didn't cause geometry to distort which was also a CRT-related problem). Today's digital video displays can get much brighter than CRTs. The highest possible Contrast setting is NOT the one that's the highest without causing white clipping. The right Contrast setting is the one that produces a white level that does not cause eyestrain. For viewing images in a completely dark room, most people find 35 fL is about right if they are sitting close enough to the TV that it fills most of their field of view. If you sit farther away, you may find that you have to reduce Contrast even more. The eyestrain comes from your eye/brain constantly fighting over whether your iris should be open to see detail in the dark shadows of your room or whether your irises should be closed in order to view the TV screen images comfortably. The constant fight between open iris and closed iris is where the eyestrain (and squinting) comes from.

It sounds like you don't own a meter. If that's the case, you don't know what 35 fL looks like, but chances are, if you turn Cell Light back up to 20 and bring Contrast down into the low 80s or so, you may end up pretty close to 35 fL but with better overall images because your brightness limiting won't kick in at 30% or 40%, it will kick in at 60%-ish instead. This will make much of your midtone area look better over a wider range of average picture levels. You can use eyestrain as an indicator of whether the screen is too bright... watch TV for 2 hours or so. If you notice eyestrain, reduce Contrast some more and take note after your next 2 hours or so of viewing whether eyestrain is better. If not,. reduce Contrast again. Since you aren't calibrating with 10-point controls, there is zero reason for you to keep Contrast set to 95.

As for LCD... Backlight has a huge effect on black level. You want the lowest USABLE Backlight setting that allows you to achieve the white level (set with Contrast) that you need (again, around 35 fL for a dark room... usually, there can be reasons for different levels). The problem with Backlight controls is that the very lowest settings may cause color problems you can't fix or that you can't fix easily. And SOME Backlights will go so low that you can't get 35 fL even with Contrast at maximum. In those cases, you will have to use a Backlight setting somewhat higher than the lowest setting, then tune your white level with Contrast. Same thing applies here though... the highest Contrast setting that does not clip white is almost never the RIGHT Contrast setting for LCD TVs. Without a meter, you cannot really tell whether low Backlight settings cause color problems or not (unless the problems are very severe and obvious). So lacking a meter, an LCD owner is best off using a Backlight setting about 2/3 of the way down the adjustment range (if the range is 0-30, a setting of 10 would be a reasonable setting most of the time). Then going back to the eyestrain test, pick a Contrast setting and note whether you are feeling eyestrain after a couple of hours or not. If there is no eyestrain after a couple of hours, raise Contrast a bit and try again. If you then get eyestrain, lower Contrast a bit and call it good. If you can NEVER set Contrast high enough to get eyestrain, you may have to raise Backlight a bit and try again... keeping in mind that you will be raising the black level at the same time, something you usually want to avoid with LCD displays. For daylight viewing, raise the Backlight as high as needed to make the images look OK. Contrast may have to be raised also but not always. Then return to the lower setting(s) for dark room viewing.
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post #15 of 75 Old 04-09-2014, 11:31 AM
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^^what i meant was that if abl kicks in only for bright scenes, and reduces that brightness so that it looks just like it would if i set the cell light to say 10 instead of 20, then it'd be a lot nicer to see a system that maintains that brightness instead of reducing 'just because'.

a cell light of 20 is way to fricken bright, the end. i'm not going to turn my contrast down to 50 to compensate for that. turning down cell light works well, but if it increases abl, that seems dumb to me. i don't want more abl, i just want a less bright image. <--- just to clarify, not debating the way it IS, but the way I WISH it wash

the 'backwards' thing is because in my mind, it seems to make more sense that increases brightness would increase abl, since the panel would not be able to maintain that higher brightness with brighter scenes.

i guess where i'm confused, is that if i pull up a test disc that is showing 'white' from say 220-255, adjusting the contrast DRAMATICALLY changes where white clips, while changing cell light does not change it at all. that's where my 'inference' came from. not the name, but how it functions(or apparently functions as the case may be).

when I get some time, I'll have to try reducing contrast and pushing the cell light back up, see if I notice a difference. I honestly haven't seen ABL, ever? so I'm not sure if that's something I just can't notice or what the deal is. I am Canadian, so I've seen plenty of winter sports on the tv already tongue.gif
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post #16 of 75 Old 04-09-2014, 11:54 AM
 
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Doug, have you had the chance to calibrate any F8500s to 35fL yet? If so could you divulge your methods for low contrast and max cell?
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post #17 of 75 Old 04-09-2014, 12:00 PM
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Quote:
Originally Posted by Doug Blackburn View Post


Seems to me that the first option is the best option, especially for those who enjoy hockey or skiing.

yes, it's preferable to leave it at 20 and deal with the hassle of multiple 10pt runs to figure out where things are lining up.
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post #18 of 75 Old 04-09-2014, 01:13 PM
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I don't know who this "Korea Engineering" is but I'm not buying this (North Korea maybe)...

Does Cell light effect ABL ? Yes, but it also changes the drive level to the panel at any picture level before ABL kicks in so it is NOT just an ABL level adjustment !!
For those of us who own a F8500 and have spent many, many hours calibrating we know that the 10 point calibration points do not line up well with contrast set to less than 95%.
I have done several experiments to see the difference between say cell @ 14 & contrast @ 95 Vs Cell @ 20 & Contrast @ say 65-70 (both having the same white level of about 36fl).
With the high cell & low contrast, the 50% adjustment ends up effecting (as memory serves) approximately 65% stimulus, 80% adj effects near 100% stimulus and 90 & 100% have no effect..
This causes a lot of banding (unevenness) in the greyscale that is easily seen in grey ramps or gradient patterns.
FYI: For all my measurements I use 21% APL patterns with a 10% window size & 5% steps.

I actually found that 100 is the best number for contrast Vs 10 point alignment but that is not for everyone since I did my 2 point cal in the service menu and adjusted RGB drive levels down a bit so contrast setting @ 100 does not ever clip white.

Since doing this I have been happy with the panel and have not been tempted to due any tweaks since early 2014....

Todd
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post #19 of 75 Old 04-09-2014, 01:38 PM
 
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^ Well I'm glad Todd has chimed in with some tech details.
I was seeing roughly the same things/problems but in a more basic sense I suppose.
All sorts of weird and wonderful things were happening to PQ and meter readings with really low contrast but max cell. I think because the F8500 goes so high in cell power, it breaks a few 'laws of plasma TV' along the way. I could not dial out high cell with low contrast and balance things.
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post #20 of 75 Old 04-09-2014, 02:18 PM
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Here's a question. Let's say you leave Cell at 20 and Contrast at 95 - can you try to hit 35-40 Fl for dark room viewing by adjusting 2pt. and 10pt. WB controls alone, by heavily subtracting the RGB values? Is it possible to decrease light output and dial in accurate grayscale? I fully admit - I'm an amateur and may be asking a dumb question.
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post #21 of 75 Old 04-09-2014, 02:24 PM
 
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^ Green is the equivalant to contrast at the high end and brightness at the low end but 20 cell luminance outplays compensation adjustments done here.
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post #22 of 75 Old 04-09-2014, 02:29 PM
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Seem like most calibration settings for the 2013 settings leave the G levels in 2 pt. at default as well. Any detriment to PQ in seriously lowering those, especially if you have a noticeable green push?
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post #23 of 75 Old 04-09-2014, 02:30 PM
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Quote:
Originally Posted by DarkHorse88 View Post

Here's a question. Let's say you leave Cell at 20 and Contrast at 95 - can you try to hit 35-40 Fl for dark room viewing by adjusting 2pt. and 10pt. WB controls alone, by heavily subtracting the RGB values? Is it possible to decrease light output and dial in accurate grayscale? I fully admit - I'm an amateur and may be asking a dumb question.

You can do this with the sub-contrast control in the service menu if it's available. That way the 10 pt. controls line up and your peak white is set to use the full range of 10-bit internal DSP codes.
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post #24 of 75 Old 04-09-2014, 02:52 PM
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Quote:
Originally Posted by zoyd View Post

You can do this with the sub-contrast control in the service menu if it's available. That way the 10 pt. controls line up and your peak white is set to use the full range of 10-bit internal DSP codes.

I did not try that but it may behave the same as regular contrast ?
When people are talking about 35-40fL, they must be talking about a full screen pattern.
I can easily get 40fL with a cell setting of 15.
I would not want to watch anything over 40fL as well cool.gif
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post #25 of 75 Old 04-09-2014, 03:15 PM
 
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You can do this with the sub-contrast control in the service menu if it's available. That way the 10 pt. controls line up and your peak white is set to use the full range of 10-bit internal DSP codes.

You never cease to amaze me with your knowledge of all this stuff wink.gif
Hats off to you!
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Quote:
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Quote:
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You can do this with the sub-contrast control in the service menu if it's available. That way the 10 pt. controls line up and your peak white is set to use the full range of 10-bit internal DSP codes.

I did not try that but it may behave the same as regular contrast ?
When people are talking about 35-40fL, they must be talking about a full screen pattern.
I can easily get 40fL with a cell setting of 15.
I would not want to watch anything over 40fL as well cool.gif

I concur with 40+fL cell 15. I like +/-45fL during the day.
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post #27 of 75 Old 04-09-2014, 03:57 PM
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Quote:
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I did not try that but it may behave the same as regular contrast ?

It reduces light output yes, but because it's before the DSP and contrast is still at 95 (or 100 in your case) the 10 pt controls remain aligned.
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post #28 of 75 Old 04-09-2014, 07:40 PM
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Quote:
Originally Posted by zoyd View Post

It reduces light output yes, but because it's before the DSP and contrast is still at 95 (or 100 in your case) the 10 pt controls remain aligned.

Makes sense now that I think about it...
It's really the same thing I did with the RGB drive controls.

Agree with Pie about King Zoyd...
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post #29 of 75 Old 04-09-2014, 09:04 PM
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you guys have definitely turned what I always thought was a tedious, but straight forward process into something I feel like I need a university degree to understand fully.

this thread has been specifically about Samsung, but does this same idea apply to most/all plasmas as well?

what order would you guys recommend adjusting settings in? I mean, I'm sure there's gonna be some back and forth, but is there a better place to start? would it make sense to do contrast first to get the desired brightness, or ?

is there any good reason to turn cell light down? or is basically just going to save you electricity?

clearly I've got some more reading to do. I've never seen a plasma specific guide to calibration, and it seems like I need to find one
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post #30 of 75 Old 04-10-2014, 05:39 AM
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What about running Cell Light 20/Contrast 95 and using the "Energy Saving" options to lower the light output?
Or would that only be the same as reducing Cell Light?
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