YCbCr color coding

[qp6019352]

Originally Posted by qp6019352

If AlbanRampon is correct in what he says and your DisplayLink adapter indeed is outputting Limited Range RGB, then it is probably caused by the graphics driver of the PC.

The Intel graphics driver allows to adjust it as well, it's explained over there for example:

http://www.avsforum.com/forum/26-hom...l-0-255-a.html

That being said: I wonder if the graphics driver really could influence what kind or RGB range the DisplayLink adapter is outputting at.

Maybe AlbanRampon can shed some light on this.

Any update?

[AlbanRampon]

Hello,

From me, no update: we still don't do any transformation.
We get a 0, we give a 0. We get a 16, we will give a 16.

As you indicated, the TV has probably a setting not matching the one from the graphics card, where pixels are being computed, or other elements in between.
The fact that nobody else reported the issue does tend to confirm this is a local issue as the chip has been shipped in millions units and has been on the market for years...

Kind regards,
Alban

[qp6019352]

I do not have seen this on DisplayLink either, was just curious.

[saintfrenz]

Yes, the Intel Graphics Control Panel does allow a choice in color space for output between RGB and YCbCr, and also between Full/Limited range for RGB,
but only if the display is connected to it directly (i.e. though the HDMI on the laptop itself).
When connected through an adapter, I cannot even see the display in the Intel Graphics Control Panel (as expected)
Even when connected directly, the color looks bad when set to RGB (irrespective of Full/Limited) and looks good when set to YCbCr.
However, my laptop has the Intel HD4000 whose pixel clock caps out at 225MHz which means it can only push 4K @ 24Hz.
That's fine for 24p video rendering but awful for desktop use with anything even as simple as a mouse movement being jittery. Hence the whole need for an adapter.

With the Vantec adapter (DL-5500), I tried video playback with hardware acceleration enabled (DXVA with LAV Decoder on Media Player Classic) but was still stuttering a lot. The TV does not have any options for changing RGB range anywhere as far as I could see.

I returned the Vantec adapter (without any more extensive testing) and got a Plugable adapter that has the newer DL-6950 chipset since I was only getting 30Hz with the DL-5500 anyway and the DL-6950 is capable of 4K @ 60Hz.

A note about the TV - every time a new device connects to it and/or connection parameters change (like refresh rate in the monitor settings or the color space in the Intel Graphics Control Panel when connected directly or the HDMI UHD color setting on TV etc)
the TV goes through a "detection" and sets the appropriate mode (one of Cable Box, Blu-ray player, Game Console, PC and Home Theatre System). "PC" mode is the only one in which you get no chroma subsampling i.e. 4:4:4 chroma. Detailed review/settings on this TV is here

https://www.rtings.com/tv/reviews/samsung/mu6300

Results with the new adapter:
1. The video playback issue is now resolved. As a bonus, I also get HDMI bitstreaming with audio. I don't know whether HDMI audio bitstreaming was possible with the Vantec adapter.
2. The color first came just as bad as the first adapter. After setting the HDMI Black Level to "Normal" (as opposed to "Low" before) and flipping HDMI UHD color off and on, it went through the "detection" again and came back with correct color. I had not tried this with the first adapter.

In short, everything is good now. I think there might be some HDMI color space/settings related "negotiation" going on when the TV connects to a device and goes though the "detection" but without further research into the TV and HDMI spec, I can't say.

P.S. from @qp6019352 description, it looked like color crush and not washed out.

[qp6019352]

First you say:

Originally Posted by saintfrenz

The TV does not have any options for changing RGB range anywhere as far as I could see.

Then you say:

Originally Posted by saintfrenz

After setting the HDMI Black Level to "Normal" (as opposed to "Low" before)

So, there is a option in the TV to change the RGB range .

Originally Posted by saintfrenz

PC" mode is the only one in which you get no chroma subsampling i.e. 4:4:4 chroma. Detailed review/settings on this TV is here

https://www.rtings.com/tv/reviews/samsung/mu6300

Yup. And PC mode will always expect RGB Full Range (0-255), the "HDMI Black Level" setting is not even available in PC Mode AFAIK.

Originally Posted by saintfrenz

P.S. from @qp6019352 description, it looked like color crush and not washed out.

Crushed/clipped black levels and colors would mean that the DisplayLink adapter is sending out RGB Full Range (0-255) and your TV is set up to expect RGB Limited Range (16-235) input. So, if you set your TV to expect RGB Full Range (0-255) input, the issue should be gone.

[saintfrenz]

Ah I see. So "HDMI Black Level" actually refers to the RGB range?
If so, how is the mapping? HDMI Black Level "Low" is RGB 16-135 Limited Range I presume?
BTW, the TV does allow switching HDMI Black Levels even when in PC mode and I can clearly tell the difference between normal/crushed colors when flipping back and forth.
Switching between PC and other modes only switches the chroma.
I should have tested further with the DL-5500 adapter. Oh well, the DL-6950 gives me 4K@60Hz so its all good.

Learnt something new. Thanks very much.

P.S. 40-43" 4K TVs look pretty sweeet as monitors

For people stumbling on to this thread later, to use the Samsung MU6300 4K TV as a monitor:

1. HDMI UHD Color: On
2. HDMI Black Level: Normal, NOT Low. Otherwise, you have color crush
3. Mode : Set to "PC" otherwise, you don't get 4:4:4 chroma
The TV only correctly sets PC mode if the refresh rate is 30/60 Hz. If its lower eg. 24Hz it does not successfully set PC mode even if set manually. At 24Hz you still get only 4:2:2 chroma.

Backlight 15, Brightness 0, Contrast 100, Sharpness 30, Color Tone "Warm2" -> these are just my preferences.

Links of relevance:

https://www.rtings.com/tv/reviews/samsung/mu6300
https://medium.com/@keredson/using-t...r-8582390bb824

[AlbanRampon]

Very interesting, thank you for posting your experience.

On the Plugable adapter using the DL-6950, we have added support for hardware mouse cursor in 8.4 M0. For a very smooth mouse cursor movement, I would recommend you use it as I expect you to feel the difference.
This feature relies on new hardware block in the DL-6950 so cannot be made available on DL-5xxx... Another good reason you had to upgrade to our latest ASIC.


We keep working on a few performance improvements. They are very long developments though, so it will take a while to reach a release.

Kind regards,
Alban

[qp6019352]

Originally Posted by saintfrenz

Ah I see. So "HDMI Black Level" actually refers to the RGB range?

Yes, I already told you this in my very first reply, see:

Originally Posted by qp6019352

On Samsung TVs, the option is usually called "HDMI Black Level", which can be set to "Low" or "Normal".

Originally Posted by qp6019352

If so, how is the mapping? HDMI Black Level "Low" is RGB 16-135 Limited Range I presume?

Yes, I think so. But as you said, you can easily see this anyway:

0-255 source on 0-255 display = all fine
0-255 source on 16-235 display = clipped black detail (i.e. details are missing) and crushed colors
16-235 source on 16-235 display = all fine
16-235 source on 0-255 display = black looks gray and everything looks washed out and bleached

Originally Posted by qp6019352

BTW, the TV does allow switching HDMI Black Levels even when in PC mode

Okay, but anyway, you should note that:

PCs always render at 0-255 RGB internally natively. Windows always renders in 0-255. Even when you switch your graphics driver to 16-235, it will simply compress 0-255 into 16-235 instead of really rendering at 16-235. So, it's always best to output at Full Range RGB (0-255) with a PC, since that is what it is natively rendering in. So, the display should also be configured to 0-255. Also, please note that PCs always render natively in 4:4:4. RGB is always 4:4:4 (full chroma and luma resolution).

16-235 is used for video content, i.e. for Blu-ray Disc, HDTV and so on. Video content usually is YCbCr, not RGB. And YCbCr is always 16-235. Besides, most video content is 4:2:0, not 4:4:4, i.e. you only get 960x540 color (chroma) resolution on a 1080p video/movie for example.