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I'm trying to calibrate an older Vizio M-series (M651d-A2R) and there no settings for RGB levels. (ie. full vs limited)

For example, I'm using PGenerator (Raspberry Pi) set to RGB Full. How can I tell if my TV is displaying that correctly? (ie. 0-255 instead of 16-235)

How would that affect my calibration of setting brightness? (where you set colors below 16 to not be visible, etc)
 

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I'm trying to calibrate an older Vizio M-series (M651d-A2R) and there no settings for RGB levels. (ie. full vs limited)

For example, I'm using PGenerator (Raspberry Pi) set to RGB Full. How can I tell if my TV is displaying that correctly? (ie. 0-255 instead of 16-235)

How would that affect my calibration of setting brightness? (where you set colors below 16 to not be visible, etc)
It depends on what your black level is set too.

Set black level to low for 16 to 235

Set to high for 0 to 255

Sent from my Pixel 5 using Tapatalk
 

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Hi,

If you're using Pgenerator, you should be able to tell whether the tv is set to Full or Limited when getting a signal from it. If you display a 10% black window with a black background (APL 0%) around it, can you see the black window as grey surrounded by black? if so, then the tv is interpreting it as Full. If this happens then you may be forced to have the Pgenerator send YCbCr instead. While it is not bit accurate, the actual error differences may be negligible depending on what your tv is doing with the signal anyhow i.e. when the PGenerator is sending an RGB signal, the tv is probably converting that to YCbCr, processing it and then converting it back (depending on what input and mode it's in) which also introduces possible error.

As they mentioned in the other thread, hopefully the tv is always in Limited mode. I looked through your manual link but didn't see anything like an HDMI Black Level option that other tvs have.

cheers,


--tom
 

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Discussion Starter #4
Thanks so much for the help!

Can you help me better understand the signal processing for limited versus full? I'm reading this Data vs. Legal TV Levels article but I'm still confused about what is actually happening.

For example, let's say I create a bitmap/image/video of true black (RGB 0, 0, 0). (ie. I use Photoshop and each pixel is actually 0, 0, 0).

If I display this image through my Raspberry Pi (or any other device) and the Pi is set to LIMITED range, does the output video actually change the pixels? For example, would this be modified before being sent and then sent as (16, 16, 16)?

If that's correct, then is it impossible to send values less than 16 during output?

(my confusion is understanding how blacker-than-black can be displayed but I think I need to understand the fundamentals above first)
 

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Thanks so much for the help!

Can you help me better understand the signal processing for limited versus full? I'm reading this Data vs. Legal TV Levels article but I'm still confused about what is actually happening.

For example, let's say I create a bitmap/image/video of true black (RGB 0, 0, 0). (ie. I use Photoshop and each pixel is actually 0, 0, 0).

If I display this image through my Raspberry Pi (or any other device) and the Pi is set to LIMITED range, does the output video actually change the pixels? For example, would this be modified before being sent and then sent as (16, 16, 16)?

If that's correct, then is it impossible to send values less than 16 during output?

(my confusion is understanding how blacker-than-black can be displayed but I think I need to understand the fundamentals above first)
Again, you should not be setting the Pi itself to limited range, as it is not accurate for either RGB Limited or YCbCr (which is always 16-235). Such range changes must be made in the software used.
Blacker-than-black is not something you need to attempt to display. It will never be visible if black is correctly adjusted.
 

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Discussion Starter #6
Yes, I'm not setting the Pi to Limited. It's set to RGB Full as you have recommended.

I'm just trying to understand how the signal is processed to help me better understand how everything is working.
 

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I'm just trying to understand how the signal is processed to help me better understand how everything is working.
Hi,

You're not alone here. :)

As I understand things, YCbCr which is what video content is encoded in and is limited to 16-235 but does not prohibit data outside that range. Your display will take the YCbCr data, process it and convert it to RGB. This is why when you display a black or white bars pattern from a calibration disc, you can see those "blacker than black" (when your brightness control is not set right) or "whiter than white" bars (typically still visible when contrast is set properly).

Within the RGB space, if a device is set to Limited or Full, it will restrict itself to that range. At this point if a device is getting a source signal with data outside the range it wants to deal with then it will either clip that data or re-scale it to fit within its range.

With the PGenerator, your source (the calibration software) is set to 16-235 yet it puts out 0-255 signal to the display. At first, it may seem counter-intuitive to tell the tv/display to expect 16-235 but the easiest way to think of it is that the Full signal is just a container and will never have anything outside 16-235 thus telling the display to expect 16-235 is exactly what you want. Otherwise, in Full mode, the display will expect 0 to be black and when it sees 16, it will display it as a dark shade of gray brighter than the display's black level. This is the final example that the Light Illusion page illustrates.

Here is an interesting post from Bob Parisseau's blog that discusses blacker than black with some of the history.


cheers,


--tom
 

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limited to 16-235 but does not prohibit data outside that range.
Except value 0 and 255 are reserved for H sync in limited rnage YCbCr, for 10 bit 0, 1, 2, 3, 2020, 2021, 2022 and 2023 are reserved for 12 bits even more. Those values are reserved in all Y, Cb and Cr components. Neither full range YcbCr (as supported in some rare digital formats like opYCC or sYCC), nor full RGB mode has such reserved values and limited has the same.
 
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