Full RBG / Limited RGB

[iSeries]

I know this topic has been beaten to death but I still have lingering doubts over a complete 'full RGB' chain being better than MadVR limited-GPU full-TV limited (ie passthrough).

I undertstand (I think) why a complete full RGB makes sense, the floating point data, so therefore less precision loss etc. But I can't help but think that, even with my LG plasma in 'PC mode' (which allows 4:4:4), it is still internally doing processing in limited range YCbCr. With a complete full RGB chain I definitely get a slight amount of crush in the first few shades above black, while MadVR limited-GPU full-TV limited is OK and the near black steps in the passthrough mode actually look identical to the output of my standalone bluray player which passes limited range YCbCr.

I don't think WTW should neccessarily be kept but I've also read that a TV transforming a full RGB signal into limited range YCbCr and then back into RGB again can cause overshoots which extend past 235, which might be a reason to keep a few steps above 235, which is of course not possible with a complete full RGB chain.

One last thing, and this is probably general ignorance on my part - I've read that modern TVs are full range RGB devices, in other words when they have done their processing they convert to full RGB for display, so 16 becomes 0 and 235 becomes 255. So I wonder then if this is the case, how is WTW ever possible?

[huhn]

full range RGB to high bit deep YCbCr is more accurate than limited range RGB to high bit deep YCbCr.

if you calibrate a Tv to show WTW you will lose CR so...

if your TV can't handle it well use something else. Panasonic is pretty inconsistent in there processing...

[iSeries]

Well the difference between clipping at 235 and showing a few extra steps up to 240 is only 2 clicks of the contrast control on my TV and I'm only actually losing 2cdm/2. So that really isn't a big deal to me. So if the argument is true that these transforms inside the TV from RGB to YCbCr back to RGB again can result in values exceeding 235, well there is a compelling reason to keep a few steps above 235 and in most cases CR loss is minimal. The other big thing for me is the near black difference with full RGB. I don't have many ideas why there would be the slight black crush in near black shades, but I can't help but think that the processing in my TV at least is optimised for limited range input and this is happening because of that.

[huhn]

you are on a plasma which makes CR measurement not 100% accurate,

and did you measure 240 as white or 235 and are you sure that's 2 CM²?

like i said panasonic processing is at best questionable.

and even if they exceeding 235 (which they do it is 240 for chroma just to show you how dumb this topic is.) they are not going to over shoot 255 so why bother?

[iSeries]

I wouldn't say it's a dumb topic, probably more dumb just to say full RGB is always best when really TVs are all different and what works best for one TV might not be best for another. If processing does cause overshoots then my thinking is those overshoots are just going to get clipped with full RGB. Madshi in the MadVR thread has actually stated that in *theory* limited range is better than full range, his words "Yeah, sure, in theory having madVR output 16-235 should be slightly better". And in fact many TVs can be a little weird if contrast is jacked up to the max so again just saying clip at 235 because there's nothing worth saving over that, is not necessarily good advice. In fact coming down a couple clicks (especially if you don't have a meter) is probably a safer option regardless of what you think about WTW.

[huhn]

why don't you quote that post directly?
because Y only is technically lossless when converted to limited range RGB where limited range would be "better".

the point is simple full range RGB is technically the highest quality you can get out of the PC. if your TV can't handle that is a different story and how should you react to that? and why should other people care a TV with full range RGB support has to be able to deal with it if not it is broken it's that simple why should there be an excuse for not properly working hardware? issue from a full range RGB signals only come from bad processing nothing else.

and most important the RGB part doesn't care about the overshooting and YCbCr is limited range for a reasons.

[iSeries]

No argument from me that full RGB is the best quality from a PC. I'm trying to make the point that TVs are not computer monitors. So really the idea that full RGB is 'best' is just another theory, because in practice I'm sure there are lots of examples where this is not true, and, as you say, is down to bad processing in the TV...which is because they are TVs, and not computer monitors, and their processing is not designed for full range input from a computer...they are designed to process limited range input from sources like cable boxes and bluray players

[huhn]

if they get a full range RGB signal they only have to convert it to something they can do that's at least 4:2:2.
so where is the problem in turning full range RGB to YCbCr 4:2:2? and yes overshooting doesn't matter.
so how do they excuse this?

i saw enough TVs that have no problem with full range RGB what so ever. and i never touched a TV that is worse with full range RGB as an input signal they where at least equal.

yeah there are TV that have problems with full range RGB you are not the irst one with a pana plasma Tv that talks about it.

and a TV is not designed for full range RGB i have to fully disagree. they support this type of signal so it is supposed to work correctly. PC modes are a normal feature of them.

[pirlouy]

Is this dumb to test if TV handles full RGB correctly with something like this: http://www.lagom.nl/lcd-test/black.php ?

[iSeries]

@pirlouy - I'll look at that later, I got a pattern from here http://www.avsforum.com/forum/40-oled-technology-flat-panels-general/2579537-lg-oleds-how-enhance-near-black-detail-3.html#post46798617 which clearly shows that full range input has clipping that isn't there when using MadVR limited>GPU full>TV limited. This difference is slight...but there is a difference.

[Asmodian]

The "full range RGB is best" always has the caveat "unless your TV cannot handle it well". In this case you are working around a failing of the TV, not simply that something else is optimal for the TV.

If that is the case then madVR limited GPU full is the next preferred option, assuming you don't mind the rest of Windows clipping.

If your TV cannot handle full range RGB well and you don't like Windows clipping then madVR full range with the GPU sending YCbCr 4:4:4 is also a good option.

[iSeries]

Would using the hidden YCbCr output option in MadVR with YCbCr 4:4:4 set on the GPU result in the GPU passing that through from MadVR as-is, or will it convert to RGB and then back to YCbCr again?

I am perfectly ok with having Windows clip as I only use this PC for video playback. So Limited>Full>Limited might be the better option for my low-end LG plasma.

EDIT: and just as a thought - could the extra 'detail' i see near-black be because of extra dithering that my plasma is performing, transforming limited range RGB to full range? and sending full range RGB is avoiding this transform and thus avoiding this extra dithering?

[huhn]

if dithering is the reason it should not come from the display it self it had to come from processing.

but this is not impossible.

[iSeries]

Just as a thought - plasmas of course dither no matter what, no avoiding it, but perhaps sending limited range it does an extra dithering step when transforming to full range as a last step? I'm just throwing out ideas...really don't know why near-black shows more 'detail' sending limited range vs full range.

[iSeries]

Well turning dithering off in madvr, full shows slightly more near black detail than limited. Turning dithering back on, limited shows slightly more detail than full. I have no idea what to make of that.

[Asmodian]

I noticed something similar with my 2010 LG plasma TV, shadow details were hard to keep. I also found sending it YCbCr or limited RGB kept levels better. Especially noticable with color steps and near black.

Which dithering option are you using? Ordered or ED1 might be a little better than ED2 in this case.

Would using the hidden YCbCr output option in MadVR with YCbCr 4:4:4 set on the GPU result in the GPU passing that through from MadVR as-is, or will it convert to RGB and then back to YCbCr again?

That option doesn't work for sending YCbCr to a display because the GPU thinks it is RGB so it will convert it to YCbCr (if set to output YCbCr) or send it as RGB so the display displays it as RGB.