RGB input to HDTV

[nautilus7]

Hi, if i understand correctly since the signal that an gpu can output is RGB and - in case we use madvr - a high "quality" RGB signal. So, ideally, an HDTV should be fed with RGB.

So, my question is, do all modern HDTVs support RGB input? Furthermore, do they display RGB signal untouched without any conversion?

In addition, i am confused what it is importance for HDTVs to accept 4:4:4 YCbCr signal. Is it because gaming consoles, such as PlayStation only output YCbCr and not RGB?

I am about buying a new HDTV for use with madvr and i am wondering if i should consider this issue.

[leeperry]

There's usually a price to pay for 4:4:4 as TV's are forced to disable their built-in post-processing meaning that you won't get anymore black frame insertion(resulting in obvious motion blur on LCD), sometimes the lack of REC709 gamut, advanced gamma correction, etc etc.

Movies are encoded in 4:2:0, of course 4:4:4 is the ideal theoretical choice but I strongly doubt that the downgrade to 4:2:0 is worth worrying about: http://www.avsforum.com/forum/166-lcd-flat-panel-displays/1381724-official-4-4-4-chroma-subsampling-thread.html
From the examples, you can clearly see quality differences (except for the “real life” image).

OTOH computer fonts do look ugly in 4:2:2 (http://s807.photobucket.com/user/floatpoo/media/444_faq/test3_a.png.html) and gamers especially want to disable pp in order to lower input lag.

[nautilus7]

Thanks for your response. I am aware of these more or less.

What I don't know and confuses me is WHY are we concered about YCbCr 4:4:4 input, if HTPCs send RGB (where such thing as 4:4:4 doesn't apply). Do HDTVs Accept RGB signal? Do they display it as is, or do they convert it again to YCbCr (loss of chroma resolution).

When site like HDTVtest (http://www.hdtvtest.co.uk/news/ue46h7000-201407153854.htm) test "Full 4:4:4 reproduction" do they mean YCbCr 4:4:4 input or something else, e.g. RGB?

[huhn]

HTPC work RGB so yes nearly all HDTV down convert to 4:2:2.
some TV support 4:4:4 unlimited RGB but you can read the rest in leeperry post. these just show how bad Tv are these days...

there so no reason that BFI didn't work in 4:4:4 RGB is just bad engineering nothing else.

When site like HDTVtest test "Full 4:4:4 reproduction" do they mean YCbCr 4:4:4 input or something else, e.g. RGB?
this means the TV has a mode with full 4:4:4 if this is not there they do 4:2:0 or 4:2:2 with all input.
this normally means RGB of cause we don't know if the TV change this to YCbCr but it's hard to fine out.

[nautilus7]

There is no such thing as "4:4:4 RGB". Chroma (sub-)sampling is valid only in YCbCr signal. Not in RGB. That's what confuses me. But I guess what you/they/all mean is that HDTVs are converting RGB or YCbCr 4:4:4 to YCbCr 4:2:2.

[huhn]

AMD still call it 4:4:4 RGB in the driver of cause you are right.

my can do full range RGB (there is no full range YCbCr in HDMI) with nearly all feature. most TV have a PC mode these days these mode can be pretty useless like the old one in samsung 60 Hz only and things like that.
or the new sony UHD TV with only 4:2:0 support at 4k and thinks like that...
most TV can do BFI backlightscanning or things like that in PC mode and motion blur is nothing funny...
this is only a problem for PC and with things like ps4 xbox one. doesn't really matter for BD player or receiver.

[leeperry]

WHY are we concerned about YCbCr 4:4:4 input if HTPCs send RGB (where such thing as 4:4:4 doesn't apply). Do HDTVs Accept RGB signal? Do they display it as is, or do they convert it again to YCbCr (loss of chroma resolution).

When site like HDTVtest (http://www.hdtvtest.co.uk/news/ue46h7000-201407153854.htm) test "Full 4:4:4 reproduction" do they mean YCbCr 4:4:4 input or something else, e.g. RGB?
They only mean that you get full chroma and that the TV won't downscale it. Whether TV's will output via a 1:1 8bit RGB pipeline when bypassing their pp is anyone's guess(I believe TMDS is somewhat lossy anyway, reason why pros use SDI), TV's internally work in 10/12bit YCbCr when their pp is enabled.

there's no reason that BFI doesn't work in 4:4:4
Input lag.

[huhn]

like BFI is faster in 4:2:2.
but disabling the backlight for each frame has no effect on the inputlag or shouldn't have. there is nothing to calculate at all the picture is not really touched.

[nevcairiel]

Its only a factor of money, they are not designed for high quality external RGB video sources, and as such they try to save money and use cheaper processing chips that only do 4:2:2.

Other than HTPCs or people with external video processors, nothing really delivers RGB video content, and game modes don't usually want any processing.

[huhn]

that's why i limited it to BFI or backlightscanning.

other processing like dynamic contrast or frame interpolation need processing power and is faster in 4:2:2 but BFI and backlightscanning?
i'm pretty sure they could do this but it is simply not important to them.

and gamer love the eizo fg2421 and strobelight hacked displays. and they don't have input lag problems X-)

[leeperry]

eizo fg2421 and strobelight hacked displays. and they don't have input lag problems
http://www.tftcentral.co.uk/reviews/eizo_fg2421.htmIf we enable Turbo 240 a small amount of additional lag is added due to the frame doubling and backlight blinking system being used. The total display lag was 18ms now, and so we can estimate the signal processing to be ~13.8ms, 4ms longer than before. Similar additional lag is added when using LightBoost backlight systems

[nautilus7]

I see.

So, since most HDTVs don't support tthe output of madvr, madvr looses most of its power, especially in blu-ray payback (no luma scaling, no deinterlacing, no proper dithering because there is a conversion to ycbcr by hdtvs).

Any 2014 hdtv model that can receive rgb input properly?

[huhn]

you can't send 4:2:0 with hdmi 1.4 or older so MadVR is not meaningless.
you have to a RGB conversation on PC .why not doing it the right way?

nearly all Tv these days have a PC mode this should supports 4:4:4 at least.

4:4:4 or rgb is no super huge thing but 4:4:4 or 4:2:2 is.

[nevcairiel]

Conversion to YCbCr in the TV is by itself not all that terrible, as good TVs do that in high enough precision, so even if it converts back and forth there shouldn't be a huge negative impact on the video.

The big problem would be subsampling to 4:2:2 in the TV.

[leeperry]

most HDTVs don't support the output of madvr, madvr loses most of its power
Make no mistake, mVR looks outstanding on a 4:2:2 TV......again their chroma downscale isn't visible on movies as they were 4:2:0 to begin with and LCD without BFI is a blurry mess to my eyes, necessary evil yada yada.

Of course the TV will internally convert to 10/12 bit YCbCr and then dither back, just pick the mVR error diffusion algorithm that's the most pleasing to your eyes and you'll be stunned all the way IME. This kind of PQ for free is a real steal.

[nautilus7]

Good to know.

At the final step, the YCbCr is converted back to RGb or not? If yes, is dithering applied to it like when it is converted by madvr? Doesn't have banding?

EDIT: leeperry was faster. So dithering IS applied.

[JanWillem32]

One type of dithering isn't equal to another.
Video processors on consumer-grade display devices really can't hold a candle to any decent PC/workstation image renderers of the last fifteen years. I have no idea why those idiots design the hardware as such.
Y'CbCr is by all means a terrible format, even 4:4:4 of whatever bit depth. I'm not going to rant much about that again, people can just read several of my older posts, such as: http://forum.doom9.org/showpost.php?p=1675373&postcount=444 . The ability of allowing 4:2:0, 4:2:2 and 4:4:4 Y'CbCr input (in whatever awful Y'CbCr type, such as BT.601 NTSC, BT.601 PAL/SECAM, BT.709 and BT.2020) from any input device should be regarded as legacy support for allowing whatever fundamentally flawed derivations of the 1953 NTSC color television standard as video input types for input devices that really can't handle anything better.
To put it this way; the bread and butter of an image renderer should be stages in a linear-light, full-coverage gamut color system that can be used to explicitly express luminance in cd/m² (XYZ, xyY, LMS and some other color systems are suitable), for advanced functionality a CAM (color appearance model) can be used to get human visual system-related color qualifiers on lightness, brightness, colorfulness, hue and such, and the last stages of an image renderer should deal with the limitations of the display device (and to lesser extent its surround parameters), which means using some form of color management to convert to display R'G'B' and high-quality dithering after that to add noise that hides some of the banding visible with mere 10-bit R'G'B' or worse, 8-bit R'G'B' display panels.
Any digital operations on the output signal by such an image renderer can only harm the quality (analog controls are generally fine). I assume that I don't need to explain why studios held on to using CRTs for such a long time for image and video editing. (Another factor that weighs into that issue are the resolutions: studio 2k is 2048×1080, not "1080p", which is 1920×1080 and normal 4k is 4096×2160. Older LCD, Plasma and some other types of display devices had very poor pixel and bit depth resolutions. Note that studio formats have never been specified with the 16:9 ratio compromise that was forced on consumer display devices, and I hope they never will be either.)
It's a shame that many of even the more expensive consumer-grade display devices butcher the input signal so much, and can't even take proper genlock on top of that. CRTs of decent quality and (semi-) professional equipment really have no such limitations. These of course have no need for the features (made of of fairy dust just to look so very flashy in the showroom to bring in more sales) that many of the consumer-grade display devices feature; their quality lies in the ability to very accurately reproduce a massive range of colors with the aid of color management (without needing any dithering in any stage to mask quantization errors) and can on top of that be easily genlocked (present images feeded to them with exactly the frame timing specified by the input device).
I would love to see all consumer-grade image standards wiped from existence in favor of the studio and professional image standards, but sadly I don't see that happen anytime soon.

[mindbomb]

if there is dvi or displayport available, I imagine those would be set to RGB by default.

[Stereodude]

Do HDTVs Accept RGB signal? Do they display it as is, or do they convert it again to YCbCr (loss of chroma resolution).
It depends on the TV and the settings on the TV. My 10 year old Hitachi RP-CRT would accept RGB 1080i60 signals via HDMI and display them without any apparent conversion to YCbCr (or it converted to 4:4:4). My new Samsung F8500 plasma will accept RGB 1080p60 via HDMI, but will convert it to YCbCr 4:2:2 (might be 4:2:0) prior to display unless you name the input with one of the two PC presets. Unfortunately the PC presets disable most of the video processing features you'd want to use. Also, the F8500 will not display 1080p24 RGB as RGB (bypassing the YCbCr step) even in the two PC modes.

At the final step, the YCbCr is converted back to RGb or not?
Of course. Modern displays use RGB primary colors to create the various color you see (with a few exceptions like WRGB OLEDs and Sharp's Quattron LCDs which have a yellow subpixel as well).

[leeperry]

It's a shame that many of even the more expensive consumer-grade display devices butcher the input signal so much, and can't even take proper genlock on top of that. CRTs of decent quality and (semi-) professional equipment really have no such limitations. These of course have no need for the features (made of of fairy dust just to look so very flashy in the showroom to bring in more sales) that many of the consumer-grade display devices feature; their quality lies in the ability to very accurately reproduce a massive range of colors with the aid of color management (without needing any dithering in any stage to mask quantization errors) and can on top of that be easily genlocked (present images feeded to them with exactly the frame timing specified by the input device).
I would love to see all consumer-grade image standards wiped from existence in favor of the studio and professional image standards, but sadly I don't see that happen anytime soon.
Simply because people want bang/bucks these days to watch 4:2:0 material and Sammy currently sell 3500:1 CR 32" 1080p TV's with BFI for 250€, at this kind of price point you don't nitpick about 12bit YCbCr processing. As much as I've stuck to CRT for as long as I could, these things flicker like hell(even at 100Hz and pushing +120Hz really is overclocking and can kill them very quickly IME), there's a price to pay for their deep black. And let's not mention their poor geometry and weight, 19" being the sane limit.

AFAIK SONY said that they would finally be able replace their good ole BVM monitors (http://www.highwayav.com/Portals/0/Products/Production_Monitors/BVM_PVM_Monitors/BVM-A14F5M/1169568028-191.jpg)(still in use in 2013 (http://s.tf1.fr/mmdia/i/33/5/plateau-speciale-10-ans-ci-26-10592335hxsqq.jpg) :devil:) by OLED's, AFAIK the main reason being the poor CR of LCD...kinda hard to master video when your black is dark gray I would guess.

[Ceremony]

might as well say this:
For those wishing to put out full range RGB on Nvidia cards: Sucks to be you.
For some idiotic reason nvidia decided to only give us RGB with the limited range of 16-235...

So what to do? Some kind people on the net provided a nice tool that fixes this idiocy for you: http://blog.metaclassofnil.com/wp-content/uploads/2012/08/NV_RGBFullRangeToggle.zip

with it, you can toggle between limited and full RGB range on HDMI out (requires restarts inbetween!). Needs to reapplied once you install new drivers of course :)

[Mangix]

madshi includes a similar tool with madVR as well. Works on Nvidia and Intel.

[nevcairiel]

Note that it's not as black and white and NVIDIA doesn't "force" limited range, it enforces whatever the display lists as it's primary format in the negotiation
On most TVs that's limited, but on my Sony TV it actually can output full range without such hacks, if I tell the Sony to request full range on that port. It's not "broken", it's just too strict of an interpretation of the spec.

[Ceremony]

madshi includes a similar tool with madVR as well. Works on Nvidia and Intel.actually, that is meant for the video color settings, not the signal hdmi output, which are two entirely different settings. the former can actually be set without any hacks in the control panel. the issue is just that the default is limited range and few users bother with it. If you are for example running firefox and a html5 video, you may end up with washed out colors unless you configure said option correctly to full range.

the later option cannot be forced to full range within nvidias control panel and relies on a registry hack.

[Mangix]

that's false. madshi's tool does exactly the same thing as the one you linked to.

[Ceremony]

that's false. madshi's tool does exactly the same thing as the one you linked to.oh right you are^^