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Setting up contrast what's the consensus

7K views 9 replies 7 participants last post by  Balthazar Lin 
#1 ·
I am reading different things about how to set up contrast and i would like to know what to do.

When setting up contrast do i want the clipping bars to stop at 235 which is the reference white, somewhere in the middle or all the way up to 255 as i can with contrast?

With my set i can get it to 250 and after that lowering contrast makes no difference anymore.

I have read to do all these different different approaches and honestly can't tell who's right and who's wrong.
Knowing that 235 is the reference white for tv it confuses me that we would set it higher because sometimes material has info above 235.
Doesn't that mean then that most of the time white is really not white then if i have my set set up at 250?
 
#2 ·
It depends on how much you care about seeing WTW (Whiter Than White).

If you don't care about seeing that, then you can push the contrast all the way up until just 235 is visible.

There is a slight problem with this though, the usual patterns won't be able to show you if you are clipping channels for 16-235.

Try the first image here: http://imgur.com/gallery/kbPbK -- Set the contrast all the way up until you see clipping or a color cast.
 
#3 · (Edited)
If you don't care about seeing that, then you can push the contrast all the way up until just 235 is visible.
Most consumer grade TVs do not have much headroom "reserved" for WTW. Typically even at the default contrast there is already some forms of clipping even if you can see all the way to 250.

There is a slight problem with this though, the usual patterns won't be able to show you if you are clipping channels for 16-235.

Try the first image here: http://imgur.com/gallery/kbPbK -- Set the contrast all the way up until you see clipping or a color cast.
You can also use the HCFR "Near White" greyscale patterns which will clearly show clipping and colour cast.
 
#4 ·
The proper setting for white is the reference white (235) and Black is reference black (16), hence the reason they are classified as "Reference".

This is the standard set for REC-709. Everyone will agree that 0~255 is for computer based devices. The so called "Super White standard" (16~254) is a sudo standard that is more a myth than the truth. There is no content material that utilizes this made up standard for Rec-709 and never will be.

Setting the display to show content above 235 is useless. DVDs and broadcast content all follow the "Broadcast Legal" standards and therefore if any content extending into the headroom area will be truncated. While minor blips into the headroom are allowed, these are not tolerated very much and content can and will be rejected and sent back to be re-edited before airing. Above all know the standards, check them out for yourself and do not rely of the opinions of others as your source of reference. How do you know if they are telling you the truth? Remember, bull**** baffles brains.

If you are ever question what the standards are, read the UTI documentations and they will set you straight. Read it carefully, as I have come across many who read something carelessly and start declaring something as a fact, only to find that they have misread the document and everything they had declared was wrong. Many times people only see what they want too see.
 
#5 ·
Randall i know that the standard sets white at 235.


On one hand i have a standard telling me it's 235 and on the other hand experienced or not people saying its best to clip it in the 240 or as high i can get it, being uneducated in the field i think im going to listen to the pros instead.

It makes me wonder then how many people are paying alot of money for bad calibrations!
 
#6 ·
I appreciate your situation but I can't help but remember the line from Star Wars # 4 (The New Hope). "Who is more foolish? The fool or the one who follows the fool?"

From my own research, I seem to have come to the conclusion that this confusion began when AVSHD-709 test disc came out. The test material seems to be okay but the documentation is sorely lacking. Upon researching the origin of the test material, it seems that two main individuals were instrumental in it's creation. The original intent was to provide a "no cost" test disc for the masses but the problem arises when it came down to the documentation. They were not technical writers and neither did the get the documentation proof read. They too seemed to appear to lack the necessary technical back ground to know what the standards should be or how to achieve it. Before this test disc came out, there was no real reference of debates as to how to set contrast and brightness.

The 240 limit seemed to possibly come from two sources. One, is based on Mark Sydow (the creator of the test material in question), who in my opinion may not be fully clear on the standards as well. In a forum entry he stated that he liked to set his settings at 240. The second is the possible confusion with the chroma limits (which can go as high as 240). An individual from SpectracCal based his rebuttal on this fact for the setting of contrast & brightness which only left me with the conclusion that he needed to do more research.

At the risk of Dominic Chan accusing me of lecturing everyone, I will state the whole secret of brightness & contrast is to understand the basic anatomy of a video signal and how to read a waveform monitor. In this case Luma is the key.


Black = 0.0007Mv. (Absolute 0 Mv. is reserved for the blanking function for the horizontal/vertical sync). White = 700 mv.

0 % or 0 IRE (Confusion exists between IRE and Percentages; essentially they are the same). 100 % or IRE

In a Rec BT-709 settings and under broadcast legal standards any possible video signal regarding Luma above 235 will be truncated and therefore adjusting a display to show anything possible Luma from 236~254 is of no value. The process of diminishing the contrast setting so that bars can be seen only serves to ****** the contrast ratio.

To help you, there are a number of tutorials on how to read a waveform monitor on the web. I have attached two links that address everything on setting up contrast and brightness from those who create the standards. The documents are from UTI. BT-814-2 and BT-815.

There is so much to say on the subject that volumes could be written but the individuals like Dominic Chan would have bases for their rants.

In my younger years I was told this bit of wisdom that gave some situations clarity, "In some cases the only difference between a professional and a amateur is one gets paid".

Strive to educate yourself all the time. Knowledge and experience will allow you to see the truth; where others do not.

Calibration is the act of measuring, comparing and adjusting to a known standard. If one decides to make and adjustment to not comply to the known standards then it is not a true calibration but a personal tweaking.

I wish I had the time, as there is so much more to say.
 
#7 ·
Personally, I like 17-255 to all be perceptible. If white is clipped in a signal, it's still going to be "true white", and if not clipped it won't be crushed.

Just like not everyone knows how to calibrate (wrong or not), not every signal was created properly (especially broadcasts!).
Also, it's easier to fix bad black levels than white levels, so the less clipping your desired settings have the more leeway a bad source has before you may feel the need to make any adjustments.
 
#10 · (Edited)
There are also many games with Superwhite on playstation. Black in limited range whn it goes lower than 16 should not be presented but white is allowed to go higher than 235 or 240. I dunno whether you should rescale the white levels or actually make white more intense (yes, 109%) as the latter in HDR can be done without any problems. Now, i dunno what displays actually support Superwhite (blacker-than-black is not supported for sure) besides this one by setting Limited 16-254 (see 5:02 timecode)
 
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