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New website page: Data vs. Legal TV Levels

 
Author Steve

INF
Male
#1 | Posted: 2 Sep 2012 11:26 
After being asked many, many times to try to explain Data vs. Legal TV Levels I have added a new info page to the website.

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

Hopefully this will help in understanding the potential problems with signal levels, especially for calibration.

Feel free to add any comments here!

Steve
Steve Shaw
Mob Boss at Light Illusion

Author pepo
ZRO
#2 | Posted: 12 May 2013 16:36 
Hi Steve,

After thouroghly reading the nice data vs tv levels, I still have a question.

Right now I calibrate (contrast & brightness) my monitor by using testpatterns that show 235 RGB and 255 RGB. I try to dial in the contrast untill I can't see the difference between the two patches. I'm I doing the right thing, considering I'm using the monitor for broadcast work? (I do the same with my brightness setting, but ofcourse I'm using 16 vs 0 RGB test images.)

Author Steve

INF
Male
#3 | Posted: 12 May 2013 17:02 
Hi Pepe,

That depends on the image path you are using...
You need to verify if you at using TV levels, or data levels as the workflow image path, and if the image is being re-scaled or not.
I would actually think the image is being re-scaled, so what you are doing is probably wrong...

Steve
Steve Shaw
Mob Boss at Light Illusion

Author pepo
ZRO
#4 | Posted: 12 May 2013 17:10 
Ok, I'm not sure if I understand everything, but I can give you an exact workflow description.

The test pattern is generated in photoshop as a tiff file. I bring it into resolve and set resolves interpretation to 'data' levels. Next I select 'legal range' in resolves monitoring ouput options.

Author Steve

INF
Male
#5 | Posted: 12 May 2013 17:33 
I don't use Resolve, so we really need a Resolve user to answer this...

But, it actually sounds like you are telling the Resolve the images are 'Data' but to output to TV Legal, so I would expect Resolve to re-map the Data to TV legal ranges, so what you are doing to set the display looks to be wrong...

Steve
Steve Shaw
Mob Boss at Light Illusion

Author pepo
ZRO
#6 | Posted: 12 May 2013 17:49 
It's like I feel forever lost with this topic, quite frustrating...

So if I would set Resolves output to full range, should I then set the contrast by looking at those test images and trying to get 235 equal to 255, visually?

Or maybe, how do I dial in a proper contrast and brightness, using some of the images downloaded from your site.

Author Steve

INF
Male
#7 | Posted: 12 May 2013 18:06 
This is a workflow understanding issue, and is not something that can easily be defined remotely.

Fixing things like this, or providing education/training, is where a day's consultancy is often required.

I can't think what else I can suggest (beyond the information on the website) without actually seeing your operation to be honest.



Steve
Steve Shaw
Mob Boss at Light Illusion

Author pepo
ZRO
#8 | Posted: 12 May 2013 19:53 
Thanks Steve, I totally understand and respect that.

And on that note, would you like to do a consultancy next time you're in Holland? maybe at IBC time? Or if not possible, could you recommend me anyone in the Netherlands that does these consultancies?

Thanks,
Pepo

Author Steve

INF
Male
#9 | Posted: 12 May 2013 20:01 
Hi Pepe, I will be at IBC, so that may be possible...

I don't know of anyone local to you that can help - maybe someone on this list can recommend someone?

But, have you checked using the CalImages you can download from the Light Illusion website?
They may help, combined with the info on the Date/TV Level info web page.

A very basic check is to look at 'black' with no signal going to the display, and then with the Brightness Cal image check for both clipping and that the blackest black in the Cal image is as black as when there is no signal going to the display.

Then check with the Contrast Cal image for white level.

And see: http://www.lightillusion.com/display_calibration.html

Steve
Steve Shaw
Mob Boss at Light Illusion

Author pepo
ZRO
#10 | Posted: 12 May 2013 20:13 
I'm still definitely interested in a consultancy, but ofcourse I would love to know what the pricepoint of such a visit is. Maybe you could sent that to my email, in case you don't want to discuss that here.

I will start reading the page again, I think it's even updated from what I read a year ago. Anyway, I'll try.

Thanks again.
Pepo

Author Steve

INF
Male
#11 | Posted: 12 May 2013 20:48 
Happy to discuss consultancy fees - the standard fee is £750 per day, plus expenses.

When we do more than one day we can, and do, discount.
And when associated with other purchases (such as LightSpace) we charge a lesser fee - £475 per day, plus expenses, as an example.

Hope this helps.

Steve
Steve Shaw
Mob Boss at Light Illusion

Author Jean COUDSI
ZRO
#12 | Posted: 14 May 2013 20:59 
Hi Pepo

I useLight Illusion CMS and RESOLVE.
With Tiff file (I suppose RGB 444 data) you normally run Data Level (see Data Levels Settings and Conversions in DaVinci Manual).
But you have to know that each clip in the Media Pool, whatever its original bit-depth or data range, is first scaled into full-range 32-bit data. How each clip is scaled depends on its Levels setting (in the Clip Attributes window if you have no confidence with the AUTO process based on the codec of the source media).

The main thing is to be sure that your monitoring is well setup in the level you define in DaVinci Resolve settings, AND this option you choose in DaVinci Resolve settings NEED to matches the data range of your monitor. Check this point if you use any AJA or Black Magic box (SDI to DVI or SDI to HDMI by example)
Otherwise, the signal will appear to be incorrect on your display even though the internal data is being processed accurately by DaVinci Resolve… The two options are :
> Video Levels when using a broadcast display set to the REC709
> Data Levels: Only if your monitor is capable of displaying “full range” video signals AND if you want to see on your monitor the FULL data range (10-bit 0-1023).

In your case, you need to test your settings to be sure.
But I believe you can do this if your monitoring and your workflows are REC709 (Scaled Video Levels) :
- Start with AUTO in clip attribute with your Tiff file and use an empty timeline called "AUTO"
- setup the monitoring on video levels
- adjust your monitor with the BarsAndBlack.tif and check with test patterns (black to 0 and withe to 25-30 FT-L on LCD or 35FT-L on CTR)
- compare the result by importing the same Tiff file in new bin in media pool. Change level in Media Pool with attributes to data levels and build a new timeline in CONFORM called "DATA" with this second tiff file
- At least redo the last operation in a third bin where you change the level to video level. And build a third timeline "VIDEO"

You normally will see no difference between AUTO and DATA. if not your tiff file is video scaled !
At this point, you can be sure what levels you see and start calibrating your monitor with all test patterns … and CMS … and a good probe.

Regards
Jean COUDSI

Author pepo
ZRO
#13 | Posted: 20 May 2013 15:47 
Hi Jean,

Thanks for your reply! I managed to get everything done, thanks again,

Pepo

Author Nepomuk
ZRO
#14 | Posted: 1 Apr 2014 06:49 
Hi Everyone,

I have a general question.
When does is make sense to work with legal levels? Wouldn't it be easier to work in full range all the time and only just scale the full range master, if a broadcast station requires it? This output would also have automatically no illegal values.

Thanks,
Nepo

Author Steve

INF
Male
#15 | Posted: 1 Apr 2014 08:49 
There is no right/wrong way to work.
It's all down to your preference and that of the material you are working with, and what the final delivery requires.

Steve
Steve Shaw
Mob Boss at Light Illusion

Display Calibration Light Illusion Forums / Display Calibration /
 New website page: Data vs. Legal TV Levels

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