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White clipping

post #1 of 12
Thread Starter 
Hi all,

Sorry for what may sound like a stupid question.

On the white clipping screen, do I want all the bars flashing ( up to 254) or just up to 234 with 235 - 254 being soid white.

I've only ever used the thx calibration on pirates of the Caribbean before.

Thanks in advance
post #2 of 12
There has been much debate about this in the past (check the AVSHD calibration disc manual for a more information). It is OK if they only flash up to 235. However, useful picture information may reside in the WTW data (so 236-254). I'm sure there is a trade of if all of them flash (I believe it is reduced light output) but I found it to be good to compromise. Just make sure they flash up to 235 and if you can, go up to 244 or so.
post #3 of 12
The real answer is... you cannot set the Contrast control with one of these discs... all you can do is find the highest possible setting you can use without clipping. Most video displays are much too bright for dark-room viewing with the highest possible Contrast setting. What you want is 30-35 fL for 100% white in a dark room. No test/setup disc can get you to that setting. You have to have a meter to know whether your 100% white brightness is set correctly or not. The meter will tell you when you have achieved 30-35 fL.

Lacking a meter, all you can do is note whether you experience any eyestrain after watching the TV for 1 to 3 hours in a dark room. If you detect eyestrain, reduce the Contrast control until it stops for at least the length of a movie. No test/setup disc will help you do that.

The discs only help you determine what the highest usable setting for Contrast is... that's useful to know, but it is likely to NOT be the right setting for the Contrast control.
post #4 of 12
I can see what you're saying Doug, but to me reducing the contrast of a display in order to reduce peak fL seems a clumsy way to do it. I know that not all displays have suitable controls for this, but reducing the backlight on an LCD TV or closing a manual iris on some projectors seems a much neater way of doing it and in some cases will increase on/off contrast too.

I've never owned a plasma display, but is there no equivalent control to an LCD backlight? I plan to replace my existing LCD TV at some point and would likely get a plasma next time, but apart from using some bias lighting to help guard against eyestrain, I'm a bit reluctant to reduce the fL by the contrast control unless absolutely necessary. DO the various modes like THX, movie, etc just reduce the contrast as well or do they do something else?
post #5 of 12
Hi Kelvin. My 2008 42-PF11EK plasma actually had too little light output when setting contrast correctly (the control was labled input level). However, the control labled as "contrast" could compress the dynamic range (this alters the gamma curve if you overdo it) and whilst this had not effect on the video levels that could be seen, it did lower or raise the light output. Perhaps newer models have similar controls.
post #6 of 12
Thanks Jeroen. I'm only familiar with calibrating JVC projectors and Sony LCD TVs which have an iris and backlight respectively. I'll probably do a fair bit of research when I do replace my TV anyway, but it's useful to know there might be alternatives to throwing away contrast. My JVC X35 is due soon, so it'll be a while before the TV gets replaced anyway...
post #7 of 12
Backlight is clearly a factor... and you probably want the lowest backlight setting that doesn't create big problems (some backlights drift, color-wise, when you dim them all the way). So you need to find the lowest usable Backlight setting to get the darkest blacks an LCD panel can deliver. At that point, the highest Contrast setting without clipping may STILL not be the right/best setting if it produces more than 30-35 fL in a dark room. So STILL, for an LCD display, the highest possible Contrast setting is not necessarily the RIGHT Contrast setting.

Samsung plasma TVs have a Cell Light control that is in the same place in their menus as the Backlight control in their LCD displays. That lets Samsung use the same menu structure for both LCD and plasma TVs. But the Cell Light control is a bogus control. Before it was introduced, plasma TVs operated as if the Cell Light control was set to it's maximum setting and any Samsung TVs with a Cell Light control should be operated with that control set to the highest available setting. That makes Contrast the only control available for setting 100% white levels in plasma displays.
post #8 of 12
Thanks for the feedback Doug. I've done a few runs to check different responses on my existing TV at different backlight levels. As you say at very low settings odd things happen, so I use the mid point of 5 (out of 10) as this gives reasonable blacks and is more stable (though the low % aren't that stable even at full backlight so I think that's another issue as it's a 5 year old early 1080p model).

If I was buying a new TV today it would probably be a Panasonic 50 or 55" model. I know they have THX modes and the like. Do these limit light output in the same way as turning down the contrast or is it something different? My TV isn't directly near a window so I don't need a daytime mode particularly, so I'm probably a rare case that I'd want a lower fL than many others, hence the method of reducing light output interests me. However I'll probably be distracted with my X35 for a good while now and if I decide to upspec to an X55 the new TV might be a very long way off. wink.gif
post #9 of 12
Thread Starter 
Thanks for the replies all.

I had a play about with it today, my tv (the 47wt50) apparently doesnt have a backlight adjuster, and it is infact adjusted along with the contrast.

I ended up with the following settings.

contrast 22
Brightness 33
Colour 30
Sharpness 5 (not sure how I decided on this as the settings go from 1 to 10 and it looked the same on all 10 settings)
C.A.T.S off
P-NR Min

I will probally increase contrast a bit as Prometheus seems a little dark, although having said that Despicable me seems perfect.

post #10 of 12
Quote:
Originally Posted by Kelvin1965S View Post

Thanks for the feedback Doug. I've done a few runs to check different responses on my existing TV at different backlight levels. As you say at very low settings odd things happen, so I use the mid point of 5 (out of 10) as this gives reasonable blacks and is more stable (though the low % aren't that stable even at full backlight so I think that's another issue as it's a 5 year old early 1080p model).
If I was buying a new TV today it would probably be a Panasonic 50 or 55" model. I know they have THX modes and the like. Do these limit light output in the same way as turning down the contrast or is it something different? My TV isn't directly near a window so I don't need a daytime mode particularly, so I'm probably a rare case that I'd want a lower fL than many others, hence the method of reducing light output interests me. However I'll probably be distracted with my X35 for a good while now and if I decide to upspec to an X55 the new TV might be a very long way off. wink.gif

Panasonic's THX modes have typically been the dimmest mode the TV offers, sometimes not being able to achieve even 30 fL in some earlier cases. When it comes to plasma TV, the TVs Contrast control and "gain" calibration controls determine how bright or dim the TV will be. If there's a Cell Light control, it's really a bogus control that should be set to Max and forgotten. For LCDs, the gain controls, Contrast and backlight determine how bright the TV gets. Some TVs have a room light sensor that changes luminance and possibly color... that should be turned off for critical viewing in a dark room, but it's not too bad for non-critical viewing in changing light conditions when the TV is de-calibrated by the light in the room anyway.
post #11 of 12
That's all useful stuff Doug. 30fL might be enough in my living room at night for my taste anyway. I'll have to see when the time comes, but as I'm now debating upgrading to an X55 instead of an X35 instead then the TV change could be delayed even further. redface.gif I do use the ambient sensor on a TV in my sunroom as otherwise I was constantly fiddling with the backlight...it's not a 'critical' viewing set anyway, though I have calibrated it as best as it's controls allow with a low backlight setting, so in the evening it is nearest to accurate.
post #12 of 12
Quote:
Originally Posted by Adamsh View Post

Thanks for the replies all.
I had a play about with it today, my tv (the 47wt50) apparently doesnt have a backlight adjuster, and it is infact adjusted along with the contrast.

Are you sure? My 55WT50 definitely has a backlight setting right under the Picture Mode (Standard/Custom/etc) setting.
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