Author Topic: Data (0-255) VS TV Legal (16-235) RGB levels  (Read 745 times)

Offline sevenz

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Data (0-255) VS TV Legal (16-235) RGB levels
« on: April 03, 2019, 22:49 »
Found this a very enriching read when i was researching about RGB range VS calibration.

It made me realise that i didn't check this impt step before I started calibration....

https://www.lightillusion.com/data_tv_levels.html
« Last Edit: April 12, 2019, 15:26 by sevenz »

Offline desray

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Re: Good read - Data VS TV Legal levels
« Reply #1 on: April 03, 2019, 23:07 »
So now do you still think clipping white above 235 is still a problem for Zidoo?

Offline sevenz

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Re: Good read - Data VS TV Legal levels
« Reply #2 on: April 04, 2019, 00:09 »
So now do you still think clipping white above 235 is still a problem for Zidoo?

I don't think so... But do advise me if i'm wrong.  =) And is it because, technically, Zidoo is a media player and meant for movie playing, it won't "need" the above 235 range? Unless for gaming, where it has video signals that display up to 255?

Pls bear with my amateur questions cos I am still trying to 100% grasp what it is trying to say to apply for different scenarios for movie watching and gaming. brain on overdrive now... ha...

Offline desray

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Re: Good read - Data VS TV Legal levels
« Reply #3 on: April 04, 2019, 06:53 »
I don't think so... But do advise me if i'm wrong.  =) And is it because, technically, Zidoo is a media player and meant for movie playing, it won't "need" the above 235 range? Unless for gaming, where it has video signals that display up to 255?

Pls bear with my amateur questions cos I am still trying to 100% grasp what it is trying to say to apply for different scenarios for movie watching and gaming. brain on overdrive now... ha...

In short, you are right. Zidoo is a media player but it does not necessary mean that it cannot display enhanced input level (0-255) else why will there even be an option for you to choose in settings. Make sense? As I’ve mentioned to you via our chats, it is best leave everything to “Auto” in your source (media player or Blu-ray player) to allow an optimum input level based on the source content you are playing.  For Zidoo, majority of the content player will be media like mkv and bd iso files etc. It does not come as a surprise to me that it limits the signal to (16-235) for all video signal which explains why you see clipping at white beyond 235. In theory and practice, to see beyond WTW range (236-255), you need to change the video level to 0-255 in Zidoo and set the display (TV or Projector to either Auto or at enhanced mode to correspond to the source level at 0-255) to see the full spectrum. But Zidoo in this case does not allow that to take place (you can call it a bug but not one that will be a “killjoy”). Remember what I say that 99% of the time, we are looking at media which usually authored at video level.

For PC gaming, Full RGB enhanced mode (0-255) will provide more specular highlights at the upper and lower end because of their ability to harness the graphics engine for more complex colours which makes gaming titles more colourful and immersive in details. You think Realtek chipset is meant for that? Hmmm.

When do you play with YCC 4:2:2, 4:2:0 or even 4:4:4? That’s a different topic for another day. But for now, I hope you understand what is happening here.



Sent from my iPhone using Tapatalk

Offline sevenz

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Re: Good read - Data VS TV Legal levels
« Reply #4 on: April 04, 2019, 17:52 »
Thanks desray. I'm beginning to understand this much better now :)

Now.... this spurred some thoughts... to understand it for calibration.

So for display calibration where it uses a laptop software, and assuming the main color output device had a HDMI in (to connect the laptop for calibration),

1) in this case, should we calibrate by having all devices in the video path set to be FULL RGB range, from the color system output device to the the display? Then after calibration, all devices set to AUTO detect for them to 'recognise' what to use and output automatically?

2) or do we still need to have separate calibration saved under different modes on our display device, for different device depending on the purpose? E.g. if it's for movies usage, all  devices in the chain to be set to LIMITED during calibration, then e.g. save under CINEMA mode on the TV. Then for gaming, all devices in the chain to be set to FULL during calibration, and then e.g. save under GAMING mode on the TV.


« Last Edit: April 04, 2019, 17:54 by sevenz »

Offline sevenz

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Re: Good read - Data VS TV Legal levels
« Reply #5 on: April 12, 2019, 15:14 »
just discovered something interesting/ could not understand fully during my calibration learning journey, pertaining to the RGB levels. Intent of sharing this is for discussion/ learning on what's happening in the video chain/ path. And in case anyone is noob in display calibration like me can avoid similar pitfalls

the video path that i had all along used for my display calibration is:
laptop GPU HDMI OUT [auto] - Oppo HDMI IN - Oppo HDMI OUT (video) [auto] - TV HDMI IN [16-235]

I used the inbuilt pattern generator in Chromapure (the video calibration software) for the patterns. The calibration outcomes were sound/normal, almost the same settings as what online calibrators have posted. And the dE were good.

Then, earlier this week, i decided to connect my laptop directly to my TV to calibrate, to see if there's any calibration performance difference when I skipped the Oppo in the video path. Like that:
laptop GPU HDMI OUT [auto] - TV HDMI IN [16-235]

But b4 i could even start, when i ran black and white level patterns from my laptop's inbuilt pattern generator, whites and blacks were crushed. I could not see the normal bars/words flashing on the white and black patterns on the previously calibrated brightness and contrast settings. I had to tune up BRIGHTNESS by +15 to see the flashing bars/words. Something was wrong!

I got worried that my previous calibrations were all wrong. But I had some reassurance because i knew my settings were close to online calibrators'. So I suspected it was due to RGB levels in the video chain. Thanks to this article and desray. 

I did a simple test by switching my TV's RGB levels to FULL RGB [0-255]. Immediately, it was back to normal - the flashing bars/words on the white and black levels patterns could be seen.

But i could not understand why I had to set my TV to 0-255 because all along, everything as ok when TV was set as 16-235 previously for past calibrations.  ???

Thanks to Desray's help, he kindly sent me a RGB switch tool for my GPU, which allowed forcing my GPU to send 16-235 or 0-255 RGB video output. From there, troubleshooting began. Findings:
Scenario 1 - laptop GPU HDMI OUT [16-235] - TV HDMI IN [16-235] >> ok
Scenario 2 - laptop GPU HDMI OUT [0-255] - TV HDMI IN [0-255] >> ok
Scenario 3 - laptop GPU HDMI OUT [0-255] - TV HDMI IN [16-235] >> Colors affected/ crushed
Scenario 4 - laptop GPU HDMI OUT [16-235] - TV HDMI IN [0-255] >> Colors affected/ crushed
Scenario 5 -laptop GPU HDMI OUT [auto] - Oppo HDMI IN - Oppo HDMI OUT (video) [auto] - TV HDMI IN [16-235] >> ok
Scenario 6 -laptop GPU HDMI OUT [auto] - TV HDMI IN [16-235] >> Colors affected/ crushed

The learning was:
>> The video output source that is connecting to the TV, needs to be the same RGB levels. If not, the colors will be crushed/ affected.
>> If calibrate for PC/gaming use, use (2)
>> If calibrate for movie use only, use (1)
>> If your TV or any device in the chain does not have a AUTO function to switch RGB levels (like my TV), we have to be very careful in setting the right RGB levels. Both during calibration, and during watching/ playing games and/or movies.

I do understand scenario (1), (2), (4)'s logic.

But i can't understand yet why scenarios (3) and (6) does not work...  ???

SO....
Question for discussion is: for scenario (3), what happens in the video chain that make it not to work? My naive thinking is, for (3), the TV will "auto clip away" RGB levels 0-15 and "above 235", so in a way, it should not affect display calibration.

And, the other thing i don't quite understand is, how come  scenario (6) cannot work but scenario (5) can work?
« Last Edit: April 12, 2019, 16:26 by sevenz »

Offline desray

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Re: Data (0-255) VS TV Legal (16-235) RGB levels
« Reply #6 on: April 12, 2019, 16:16 »

Findings:
Scenario 1 - laptop GPU HDMI OUT [16-235] - TV HDMI IN [16-235] >> ok
Scenario 2 - laptop GPU HDMI OUT [0-255] - TV HDMI IN [0-255] >> ok
Scenario 3 - laptop GPU HDMI OUT [0-255] - TV HDMI IN [16-235] >> Colors affected/ crushed
Scenario 4 - laptop GPU HDMI OUT [16-235] - TV HDMI IN [0-255] >> Colors affected/ crushed
Scenario 5 -laptop GPU HDMI OUT [auto] - Oppo HDMI IN - Oppo HDMI OUT (video) [auto] - TV HDMI IN [16-235] >> ok
Scenario 6 -laptop GPU HDMI OUT [auto] - TV HDMI IN [16-235] >> Colors affected/ crushed

The learning was:
>> The video output source that is connecting to the TV, needs to be the same RGB levels. If not, the colors will be crushed/ affected.
>> If calibrate for PC/gaming use, use (2)
>> If calibrate for movie use only, use (1)
>> If your TV or any device in the chain does not have a AUTO function to switch RGB levels (like my TV), we have to be very careful in setting the right RGB levels. Both during calibration, and during watching/ playing games.

I do understand scenario (1), (2), (4)'s logic.

But i can't understand yet why scenarios (3) and (6) does not work...  ???



First and foremost, I must commend your tireless efforts to try new things...kudos! Keep it up!

I'm not going to delve into the details but I just wanted to point out the obvious...

Let's recap your findings:
Scenario 1 - laptop GPU HDMI OUT [16-235] - TV HDMI IN [16-235] >> ok
Scenario 2 - laptop GPU HDMI OUT [0-255] - TV HDMI IN [0-255] >> ok
Scenario 3 - laptop GPU HDMI OUT [0-255] - TV HDMI IN [16-235] >> Colors affected/ crushed
Scenario 4 - laptop GPU HDMI OUT [16-235] - TV HDMI IN [0-255] >> Colors affected/ crushed

You say you don't understand the rationale on Scenario 3 BUT you do understand the rationale of scenario 1 & 2 ?!?! If you don't understand Scenario 3, that only shows you barely understand Scenario 1 & 2 as well :P Put a little more thoughts into your thinking cap and see whether you can figure it out...its really obvious...trust me.

Let me give you a hint - EDID of an intermediary device (in this case, your Oppo player)...another clue, some AV enthusiasts like to use something in between the source and the display (i.e. your OLED TV)



Do a little googling and then come back here with your answers :)
« Last Edit: April 12, 2019, 16:17 by desray »

Offline sevenz

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Re: Data (0-255) VS TV Legal (16-235) RGB levels
« Reply #7 on: April 12, 2019, 16:23 »
You say you don't understand the rationale on Scenario 3 BUT you do understand the rationale of scenario 1 & 2 ?!?! If you don't understand Scenario 3, that only shows you barely understand Scenario 1 & 2 as well :P Put a little more thoughts into your thinking cap and see whether you can figure it out...its really obvious...trust me.


mmmm.... My naive perception is, for (3), the TV will "auto clip away" RGB levels 0-15 and "above 235" (the BTB and WTW) when the video signal is sent to the TV. And not "map" 0-255 to 16-235.... Unless, it maps instead of "clip away"? ha... pls bear with me
« Last Edit: April 12, 2019, 16:28 by sevenz »

Offline desray

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Re: Data (0-255) VS TV Legal (16-235) RGB levels
« Reply #8 on: April 12, 2019, 16:29 »
mmmm.... My naive thinking is, for (3), the TV will "auto clip away" RGB levels 0-15 and "above 235" when the video signal is sent to the TV. And not "map" 0-255 to 16-235.... Unless, it maps instead of "clip away"? ha... pls bear with me

Nope, that's not naive thinking...it makes sense. So don't sweat it. But it is incorrect. Try again :)

See what's missing and the addition in the video chain?...I already gave you hints - HDFury and Oppo...what are those? I want you to figure it out yourself, that way, it will ingrain to your mind as you are the one who discover the answer to your own query. :)
« Last Edit: April 12, 2019, 16:30 by desray »

Offline sevenz

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Re: Data (0-255) VS TV Legal (16-235) RGB levels
« Reply #9 on: April 12, 2019, 16:37 »
Thanks Desray. I went to reread the lightillusion article. I think i understand now. It does not just "cut away" per se. But it maps and rescales it.

Like the below (extracted from the article):

=====================
The following diagram shows a configuration problem with incorrect matching of full range Data output from the colour system to a display that expects TV legal level input.


In this configuration the colour system is outputting full range Data levels, but the display is expecting TV Legal levels as its input, and is therefore clipping the black backs below 16/64, and clipping white above 235/940 as it expands 16/64 to black and 235/940 to white.

The following diagram shows a configuration problem with incorrect matching of the output of the colour system signal level, where internal full range Data images are clipped to TV legal levels on output, going into a display expecting TV legal levels.

======================