Contrast ftL setting for LCD dsiplay calibration - AVS Forum
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post #1 of 19 Old 08-10-2014, 09:37 AM - Thread Starter
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Contrast ftL setting for LCD dsiplay calibration

I just calibrated my Sharp LCD using 40 ftL as the setting for contrast when reading 100 ire window. Completed the calibration and set the grayscale, primaries and secondaries so all were within dE of 3.

My problem is that after these adjustments, the picture is just not bright enough. Perhaps in a dark room, calibrating at 40 ftL is accurate and visually pleasing but watching the display during the day is not.

How high can I go with the contrast ftL and set it before I set the primaries and secondaries?

Thanks!
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post #2 of 19 Old 08-10-2014, 10:51 AM
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Greetings

Give this article a read ...

http://www.tlvexp.ca/2012/01/setting...u-might-think/

Follow the three rules for setting contrast ... looks like you did not do that.

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post #3 of 19 Old 08-10-2014, 12:16 PM - Thread Starter
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Quote:
Originally Posted by Michael TLV View Post
Greetings

Give this article a read ...

http://www.tlvexp.ca/2012/01/setting...u-might-think/

Follow the three rules for setting contrast ... looks like you did not do that.

Regards
Hi Michael, thanks for the reply. Using a colorimeter I'd like to try and use actual numbers etc. to dial in grayscale, primaries & secondaries. Most certainly I want to start with Contrast and Brightness first before moving on the grayscale tracking and primary/secondary adjustments.

Based on the article you provided. I seem to think it would be best to use the AVSHD disc patterns to set the contrast so no clipping occurs. I did this and found that with backlight set to the STD or 0 setting I was able to adjust contrast to +20 and see all white levels from 230 - 253 blinking in the pattern. 252 & 253 are barely noticeable but there.

So now with the Contrast to not clip and no obvious discolorations when viewing 5% step gray color ramps, should I now be ready to use my colorimeter to dial in the color temp & gray scale tracking?
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post #4 of 19 Old 08-10-2014, 12:16 PM
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Quote:
Originally Posted by carillon View Post
I just calibrated my Sharp LCD using 40 ftL as the setting for contrast when reading 100 ire window. Completed the calibration and set the grayscale, primaries and secondaries so all were within dE of 3.

My problem is that after these adjustments, the picture is just not bright enough. Perhaps in a dark room, calibrating at 40 ftL is accurate and visually pleasing but watching the display during the day is not.

How high can I go with the contrast ftL and set it before I set the primaries and secondaries?

Thanks!
Generally, on an LED/LCD you want to set contrast to the highest setting that doesn't cause clipping, discoloration, grayscale or other color tracking issues, etc. Basically the highest setting that doesn't cause any calibration problems (some which require a meter/calibration software to notice). Then, you set backlight to get the desired light output. 30-40 fL for a dim to dark room with a bias light is a common recommendation, but if your environment is brighter and/or you simply want a brighter image, feel free to set backlight higher as desired. Of course, once you do that you should recheck brightness/contrast/gamma/grayscale/gamut etc. to check for any issues and/or make any necessary tweaks.

Sometimes setting backlight too high or too low can also cause calibration problems, which I why I recommend checking all aspects of your calibration once settling on a backlight setting.


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post #5 of 19 Old 08-10-2014, 12:43 PM - Thread Starter
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Quote:
Originally Posted by PlasmaPZ80U View Post
Generally, on an LED/LCD you want to set contrast to the highest setting that doesn't cause clipping, discoloration, grayscale or other color tracking issues, etc. Basically the highest setting that doesn't cause any calibration problems (some which require a meter/calibration software to notice). Then, you set backlight to get the desired light output. 30-40 fL for a dim to dark room with a bias light is a common recommendation, but if your environment is brighter and/or you simply want a brighter image, feel free to set backlight higher as desired. Of course, once you do that you should recheck brightness/contrast/gamma/grayscale/gamut etc. to check for any issues and/or make any necessary tweaks.

Sometimes setting backlight too high or too low can also cause calibration problems, which I why I recommend checking all aspects of your calibration once settling on a backlight setting.
Thanks for the reply and advice... I guess I'm struggling a bit when it comes to setting the contrast. When using the AVSHD disc to set Contrast I can get similar lack of clipping results by leaving Contrast set at +20 and Backlight can be at 0 or +16 and the clipping does not change. I can barely see 252 & 253 blinking at either Backlight setting.

So, should I just keep the contrast at +20 where I can barley see 252 & 253 blink and then just adjust Backlight to my taste?
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post #6 of 19 Old 08-10-2014, 12:53 PM
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Greetings

When you get the user controls set to where you are comfortable ... go do the grayscale. Then come back to check the brightness and contrast again when the WB is done. Usually not much changes there, but you never know since wB controls are contrast and brightness controls.

Then move onto color, realizing that the cms controls in the TV may not work as perfectly as you might think or wish.

Regards
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post #7 of 19 Old 08-10-2014, 01:20 PM
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Quote:
Originally Posted by carillon View Post
Thanks for the reply and advice... I guess I'm struggling a bit when it comes to setting the contrast. When using the AVSHD disc to set Contrast I can get similar lack of clipping results by leaving Contrast set at +20 and Backlight can be at 0 or +16 and the clipping does not change. I can barely see 252 & 253 blinking at either Backlight setting.

So, should I just keep the contrast at +20 where I can barley see 252 & 253 blink and then just adjust Backlight to my taste?
does contrast +21 and up start to clip or discolor any of the bars?


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post #8 of 19 Old 08-10-2014, 01:40 PM - Thread Starter
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Originally Posted by PlasmaPZ80U View Post
does contrast +21 and up start to clip or discolor any of the bars?
Greater than +20 and I lose the ability to see 252 & 253 blink. +20 is right on the edge.
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post #9 of 19 Old 08-10-2014, 04:43 PM
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Couple of things to consider to possibly tweak contrast a bit higher as it pertains to clipping and quality of the final picture.


One, people debate whether or not clipping at 235 or greater really makes any difference to the final picture, so you might increase your contrast setting and see if the resultant increased contrast, which causes noticeable positive changes to perceived and measured image quality, adversely affects measured color accuracy.


Two, many sets have the factory Color (saturation) control set too high. This, as well, affects clipping. If the Color control can/should be lowered, it may allow an even higher contrast setting on your set. This is the case on my Sharp. There is a recent thread here on setting Color and Tint or just check out Chromapure's site.
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post #10 of 19 Old 08-10-2014, 04:50 PM - Thread Starter
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Originally Posted by T3b_vat View Post
Couple of things to consider to possibly tweak contrast a bit higher as it pertains to clipping and quality of the final picture.


One, people debate whether or not clipping at 235 or greater really makes any difference to the final picture, so you might increase your contrast setting and see if the resultant increased contrast, which causes noticeable positive changes to perceived and measured image quality, adversely affects measured color accuracy.


Two, many sets have the factory Color (saturation) control set too high. This, as well, affects clipping. If the Color control can/should be lowered, it may allow an even higher contrast setting on your set. This is the case on my Sharp. There is a recent thread here on setting Color and Tint or just check out Chromapure's site.
Thanks for the reply... when using the AVSHD disc to set the contrast I then measure white 100 ire with my colorimeter and it reads 64 ftL. This is well beyond the 40 ftL measure that is generally accepted as spec.

At any rate, I can work with this and set Brightness, then move to color temperature/gray scale adjustments.
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post #11 of 19 Old 08-12-2014, 08:54 AM
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Quote:
Originally Posted by carillon View Post
Thanks for the reply... when using the AVSHD disc to set the contrast I then measure white 100 ire with my colorimeter and it reads 64 ftL. This is well beyond the 40 ftL measure that is generally accepted as spec.

At any rate, I can work with this and set Brightness, then move to color temperature/gray scale adjustments.
however, you can turn down backlight if 64 fL is too much, which has the side effect of better black levels


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post #12 of 19 Old 08-12-2014, 10:02 AM - Thread Starter
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however, you can turn down backlight if 64 fL is too much, which has the side effect of better black levels
Thanks for the reply, I really don't know the best way to proceed I guess. I'm a numbers guy and I would love to set Contrast and Brightness based on colorimeter readings but I'm not sure what targets to shoot for.

So, I could use the AVSHD to set Contrast and Brightness with the patterns to do so and then work on the grayscale tracking etc?

Anyone who could point me in the direction of ftL and Y numbers for Contrast & Brightness in a daylight room setting I would be greatly appreciative.
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post #13 of 19 Old 08-12-2014, 10:08 AM
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how bright does your room get during the day?


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post #14 of 19 Old 08-12-2014, 11:26 AM - Thread Starter
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Originally Posted by PlasmaPZ80U View Post
how bright does your room get during the day?
Unfortunately the windows face due south with no curtains or blinds. So it's pretty bright in that room most all day. Check the attached rough diagram. Fortunately the TV is tucked in a corner and never gets direct sunlight from the windows.
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post #15 of 19 Old 08-12-2014, 12:38 PM
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Michael,

What are your thoughts on the idea that setting contrast too high can create banding, due to the 8 bit color depth.

Suppose that you have a display that can run at 300 nits without sacrificing black level and without introducing color shift. Also suppose that there is no eye fatigue and that the luminance function fits BT.1886 (or whatever desired funciton) perfectly.

With only 8 bits to work with, surely such a high dynamic range will stretch the video levels such that there is unsightly banding between successive video levels.

In your experience, does this become an issue with higher peak luminances?
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post #16 of 19 Old 08-13-2014, 09:26 AM
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Unfortunately the windows face due south with no curtains or blinds. So it's pretty bright in that room most all day. Check the attached rough diagram. Fortunately the TV is tucked in a corner and never gets direct sunlight from the windows.
sounds like 60 fL or more might be fine in that case... I'd recommend setting backlight by eye in your case (to a level that is bright enough but doesn't cause eye strain easily)


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post #17 of 19 Old 08-13-2014, 09:46 AM - Thread Starter
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Originally Posted by PlasmaPZ80U View Post
sounds like 60 fL or more might be fine in that case... I'd recommend setting backlight by eye in your case (to a level that is bright enough but doesn't cause eye strain easily)
Yesterday I visually set the Contrast and Brightness based on the patterns to do so from the AVS HD disc. Once I was done, I measured 100% white and it registered just over 58 ftL so I have decided to go with that.

I then did a grayscale run in HCFR. I was able to get dE below 3 on all but 2 of the 10 measurement points which I felt good about since the TV only offers 2-point correction. I'll have a look at primaries and secondaries later today.

Thanks!
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post #18 of 19 Old 08-14-2014, 11:21 PM
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My Sharp has the OPC setting that changes backlight based on how much sun is coming through. So when it's bright outside, it goes to 60fL and when the sun is gone, it goes to 40fL. Too bad it doesn't work for house lighting.

That being said, Sharps suck for calibration. The CMS tend to be broken and my grayscale is nowhere near linear. And my TV crushes blacks even with brightness set correctly. It's just weird man.
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post #19 of 19 Old 08-15-2014, 05:02 AM - Thread Starter
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My Sharp has the OPC setting that changes backlight based on how much sun is coming through.
I have OPC turned off so it doesn't do that. I'm pretty happy with my calibration. As stated previously, it's not dead-on perfect but pretty good.
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