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Old 01-17-2018, 12:44 PM   #1
saintfrenz
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Default YCbCr color coding

Hello,

I have a Samsung MU6300 4K TV connected to my laptop via the Vantec USB 3.0 To HDMI 4K Display Adapter which uses the DL-5500 chipset. I have two problems:
1. The desktop looks awful with the colors all washed out. Is there any way to set the color coding to YCbCr (instead of RGB which I think is what is being used currently)?
2. Video played on my laptop (VLC, MPC) etc have horrible stutter and tearing. Any settings I need to do to fix that?

Thanks.
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Old 01-18-2018, 10:13 AM   #2
AlbanRampon
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Hello,

That adapter does NOT do ANY colour correction today. This means it displays what it gets. I advise you change the TV settings so colours are displayed properly. Other settings on the adapter were decided by the manufacturer and are not changeable.

For the video, try Film and TV which runs with GPU acceleration. For my Intel i7 Surface Pro 3 on Windows 10, a 4Kp60 video decoding is awful on the native display with VLC and all smooth with Microsoft Film and TV.

Regards,
Alban
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Old 01-20-2018, 12:49 PM   #3
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Quote:
Originally Posted by saintfrenz View Post
1. The desktop looks awful with the colors all washed out. Is there any way to set the color coding to YCbCr (instead of RGB which I think is what is being used currently)?
There are two kinds of RGB:

1. RGB Full Range (0-255)
2. RGB Limited Range (16-235)

It sounds like your DisplayLink adapter outputs RGB Limited Range, whereas your TV expects to receive RGB Full Range, which makes black look more like gray and makes everything look washed out (the other way around it would clip black detail and make colors look crushed).

Just tell your TV that it receives RGB Limited Range. Most TVs allow to do this.

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

Also:

Quote:
Originally Posted by AlbanRampon View Post
That adapter does NOT do ANY colour correction today. This means it displays what it gets. I advise you change the TV settings so colours are displayed properly. Other settings on the adapter were decided by the manufacturer and are not changeable.
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.

Last edited by qp6019352; 01-20-2018 at 12:53 PM.
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Old 01-24-2018, 11:29 AM   #4
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Quote:
Originally Posted by qp6019352 View Post
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?
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Old 01-25-2018, 02:24 PM   #5
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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
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Old 01-26-2018, 12:36 PM   #6
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I do not have seen this on DisplayLink either, was just curious.
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Old 01-27-2018, 03:30 PM   #7
saintfrenz
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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.
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Old 01-28-2018, 01:27 PM   #8
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First you say:

Quote:
Originally Posted by saintfrenz View Post
The TV does not have any options for changing RGB range anywhere as far as I could see.
Then you say:

Quote:
Originally Posted by saintfrenz View Post
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 .

Quote:
Originally Posted by saintfrenz View Post
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.

Quote:
Originally Posted by saintfrenz View Post
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.
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Old 01-28-2018, 10:38 PM   #9
saintfrenz
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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
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Old 01-29-2018, 08:32 AM   #10
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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
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