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0-255 or 16-235. What's the point?

post #1 of 11
Thread Starter 
I have been reading a ton about the difference between Full and Limited range. I still have a question or two about this and I hope someone can straighten me out.

According to this article (http://www.audioholics.com/tweaks/calibrate-your-system/hdmi-black-levels-xvycc-rgb),
Quote:
ALL video stored on modern discs, be it DVD or Blu-ray, are stored as YCbCr with a range of 16-235.
and
Quote:
First, set your source components to output YCbCr if there is an option. Second, get a test disc that has a Blacker-than-Black pattern (AVIA Pro, Digital Video Essentials, any THX DVD with THX Optimizer, etc) and ensure that you can see blacker-than-black on your display. Third, switch your display's HDMI setting from 'Normal' to 'Enhanced' if you do not see the Blacker-than-Black pattern. As long as you can see a below black signal, you are more than likely set up to get the best possible dynamic range from your display. Your final step in resolving this issue should be to set the correct black and white levels.

Again - make sure you can see below black levels in your system, and then calibrate your display to set your black and white levels. This should allow you to enjoy the full benefits of your display and get the most dynamic range out of your DVDs.

Here is my question: If I can see the black bars and white bars above and below 16 & 235, but then calibrate so that these aren't seen (as I've seen in all the instructions I can find), then what is the difference? It seems to me that now all of these extra blacks and whites are calibrated out of the picture. What am I missing?

kazooless
post #2 of 11
Quote:
Originally Posted by kazooless View Post

I have been reading a ton about the difference between Full and Limited range. I still have a question or two about this and I hope someone can straighten me out.
According to this article (http://www.audioholics.com/tweaks/calibrate-your-system/hdmi-black-levels-xvycc-rgb),
and
Here is my question: If I can see the black bars and white bars above and below 16 & 235, but then calibrate so that these aren't seen (as I've seen in all the instructions I can find), then what is the difference? It seems to me that now all of these extra blacks and whites are calibrated out of the picture. What am I missing?
kazooless

Well you're not suppose to clip above 235, you're suppose to let it run all the way to 255.

The reason for 16 being the black level has to do with the way they used to process analog video. It's a relic of that era that we didn't manage to shake in the transition to digital.
post #3 of 11
Thread Starter 
So, you're saying clip the black but not the white? And if so, then that would give you a much better picture than a device that only does the limited range can give you?
post #4 of 11
Thread Starter 
oops, it duplicated a second posting. Sorry. Don't see a delete here.
post #5 of 11
Quote:
Originally Posted by kazooless View Post

So, you're saying clip the black but not the white? And if so, then that would give you a much better picture than a device that only does the limited range can give you?

It doesn't give a "much" better picture, but there are many YCbCr triplets that when converted to RGB exceed 235. The Cb and Cr channel goes from 16-240 actually, but even at only 16-235 the YCbCr data can convert to >235.

That said the amount of visual information isn't great, but since it can be there, you should be calibrated to display it correctly.
post #6 of 11
@sotti,

Do you have any tips for HTPC users? Most video cards can't display WTW/BTB. I have to check for clipping using my PS3.
post #7 of 11
Quote:
Originally Posted by rahzel View Post

@sotti,
Do you have any tips for HTPC users? Most video cards can't display WTW/BTB. I have to check for clipping using my PS3.

ATI cards in YCrCb will pass WTW and BTB for Blu-rays played on a commercial player ( powerDVD, arcsoft, ect...)
Haven't played with nvidia cards much, or built-in intel stuff. Also if you are using something like MPC-HC or something like that to play the mpeg4 streams right off the disc/iso then the ATI card will clip BTB and WTW.

With HTPCs you basically have to play the hand you're dealt. If you don't give a rip about your desktop, games, web browser, HTPC GUI front end, and if your EDID handshake doesn't override it, using RGB full range 0-255 then having content playback in 16-235 would give you optimal BTB and WTW on everything. I don't do that with my HTPC too much sacrifice for too little gain. RGB limited or YCbCr is a bit of wash, but one or the other might work better with your equipment.

Basically when it comes to aligning content you know >235 is clipped and <16 is clipped and you live with it. You can't test it because you can't generate a pattern to see it. For brightness just make sure you can see 2% and for contrast that their isn't any discoloration and steps below 235 are visible.
Edited by sotti - 10/19/12 at 11:11pm
post #8 of 11
Thanks.
post #9 of 11
You may find this page interesting.

http://www.lightillusion.com/data_tv_levels.html

Data and TV Legal are the terms use din the professional industry, but equate to 'Full' and 'Limited'.

There are other calibration associated pages within the website that are worth looking over too.

And we are always happy to answer specific questions - so feel free to ask!

Cheers,

Steve
post #10 of 11
Thread Starter 
The reason I was asking is because I've been playing around with my HTPC. I have an Epson 8350 projector (and LOVE IT!!!). I discovered my Intel HD Graphics G45 isn't the greatest. I've read all about the Intel driver problems and have been trying to decide if it is worth upgrading to an ATI card. But I would have to get a new motherboard, cpu, ram & ATI card to do it. I don't think it is worth it since everything runs perfectly fine already.

But, here is what I've discovered. (I borrowed a PC from work with a newer Intel Graphics 2000 card, as well as an ATI 6450).

The Intel Graphics can't display the BTB or WTW with either version. The newer Intel can calibrate better though with the Epson.

The ATI Graphics can display the BTB and WTW. It looks best when it is set to output limited and the Epson is set to Expanded.

Currently, with my Intel G45, I have the Epson on Normal and I've calibrated to that with the Disney Wow and AVSHD disc. I don't have a calibration unit, so I've had to use the blue filter. So, I can't display BTB or WTW, but now that I've calibrated, I LOVE my picture. It is way better than before and I loved it before. Watching Prometheus on Blu-Ray was breathtaking. Wow.

But I can't help but wonder just how much better it would be with the ATI card. biggrin.gif

kazooless
post #11 of 11
Quote:
Here is my question: If I can see the black bars and white bars above and below 16 & 235, but then calibrate so that these aren't seen (as I've seen in all the instructions I can find), then what is the difference? It seems to me that now all of these extra blacks and whites are calibrated out of the picture. What am I missing?
kazooless

You calibrate them out to set the optimal brightness setting (lower mapping point from video signal to some physical quantity that's driving the display). Setting too low, you miss shadow detail (shadow detail invisible). Setting too high, you lose dynamic range (washed out, shadow too bright, etc). You want to set this lower mapping point so that any changes in shadow detail level in the video signal is reflected on the display.

I feel having access to the BTB signal allows you to zero in on the optimal brightness setting better than if you only have access to the positive signal. I've seen both, and find it easier to calibrate my TV if the device output the BTB signals. If the device don't output BTB, then I can't really be certain that the shade of gray I see on 17 (or 4% or whatever the disc is using) is correct, or a bit too high or too low. Having access to those BTB, or negative signals, provides much more data to work with during calibration.

This is also why ambient lighting is important. That setting you have at night, where you see 17 but not 16, might be incorrect during the day if you can't see 17, 18, etc.. You want a setting that allows you to see the shadow signals in the viewing condition you are in. Since this depends on your viewing environments, it's impossible for the manufacturer to set optimally at factory.
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