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post #1 of 45 Old 04-11-2016, 08:45 PM - Thread Starter
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RGB vs. RGBW LCD and the 4K Ultra HD Designation

Regardless of how fancy or basic the features on UHD TVs are, the common foundation they share is a resolution of 3840x2160 pixels—the UHD pixel resolution. Add HDCP 2.2 and the ability to handle up to 60 frames per second at that resolution, and you've got a 4K Ultra HD TV as defined by the CTA (Consumer Technology Association, the folks who produce CES). The purpose of the accompanying logo is to assure consumers that the TV they are buying can properly handle UHD video.


The 4K Ultra HD logo.

Last year, there was a kerfuffle regarding whether or not certain LCD TVs from LG—which used a novel RGBW sub-pixel arrangement—can actually achieve UHD resolution. Digital ink was spilled in various forums and publications arguing the pros and cons of the technology. Unsurprisingly, Samsung took a critical stance, and LG defended its new LCD panels from that criticism.

Unlike LG's OLED TVs, in which each pixel includes a white sub-pixel in addition to red, green, blue, its RGBW LCDs are based on a scheme where every fourth sub-pixel in a row is white, which means that each white sub-pixel is shared by adjacent pixels. This arrangement requires the panel to jump through some hoops in order to render 3840x2160 UHD video.

Because of their peculiar sub-pixel arrangement, RGBW LCDs cannot achieve full UHD resolution in color, they can only pull it off with monochromatic resolution test patterns. LG does not deny this; rather, the company argues that achieving UHD resolution is really only important for the luma channel (brightness). However, when I recently checked out an LG RGBW UHDTV, my findings called into question how effectively it can render monochromatic UHD resolution.

Quite literally, reading the fine print is at the core of the RGBW-versus-RGB debate. If the critics are correct, the shared white sub-pixel arrangement renders RGBW TVs incapable of achieving true UHD resolution—defined by the CTA as 3840x2160 active pixels with 8-bit color. This negatively impacts the rendering of fine text, making it a bit fuzzier, which is especially noticeable when a TV is used as a PC monitor.

There's also a figurative element to the debate, in that it's really about what defines resolution. Is it discrete pixels? Or is it subjective perception that matters, as long as a TV can ingest UHD video and output something sharper than a 1080p HDTV?

One thing I have discovered for sure, RGBW LCDs produce some funky anomalies when working with 4K test patterns. It's not too tough to find moire patterns in what should be seen as solid, uniform colors.

You may wonder whether this issue matters to a typical TV viewer. As you would expect, LG had denied that RGBW presents any problems at all. Since image-quality issues are in the eye of the beholder, I spent some time experimenting with an LG UH6150 RGBW LCD. It's listed as a 4K Ultra HD TV on the LG website, which explicitly claims that it offers 8.3 megapixel resolution "for 4x the Resolution of Full HD TVs." I compared how it rendered various test patterns—plus real-world content—to a couple of Samsung RGB LCD UHDTVs: a JU6400F and a JU7100F.

I tested the TVs using a variety of sources including a DVDO AV Lab TPG 4K signal generator, a PC sporting an NVIDIA GTX980 video card and a Samsung UBD-K8500 Ultra HD Blu-ray player. To ensure each TV received the same signal, I used a Cable Matters UHD 4-port HDMI splitter.

Let's start with one of the simplest test patterns, a 1-pixel checkerboard grid coming from the DVDO. On the RGB LCDs, that pattern looked gray and uniform—no surprise, since the pattern consists of 50% white and 50% black pixels. On the RGBW LCD, instead of gray, I saw hue-shifted vertical stripes (alternating between green and magenta) that were several pixels wide. I had trouble counting exactly how many pixels wide because with LG's RGBW sub-pixel arrangement, it was tough to tell where one pixel ended and another pixel began.


RGB LCD sub-pixels handled a 1-pixel checkerboard pattern much better than RGBW LCD sub-pixels did (actual photos).

There was no such ambiguity with the RGB LCD panels, where each black and white pixel was clearly defined and discrete. Furthermore, the RGB panels rendered the pattern perfectly in both PC mode (with 4:4:4 color) and other modes (4:2:2 color), while the RGBW panel had issues regardless of whether it was in PC mode or not.

If an RGBW LCD can't reproduce a simple monochromatic checkerboard pattern accurately, how can it claim to achieve true UHD resolution? Apparently, because it can render a vertical black-and-white alternating-line pattern at 3840-pixel resolution, and also a horizontal alternating-line pattern at 2160-pixel resolution. I saw this with my own eyes! However, when I flipped between those two patterns I noticed a huge shift in hue, when in reality both patterns should have remained neutral gray since, like the checkerboard pattern, they consist of 50% black and 50% white pixels.

The crux of the debate comes down to what defines a pixel. If it's just a hypothetical concept, a mere proxy for a subjective experience, then perhaps RGBW LCD could be considered capable of rendering some flavor of UHD resolution. However, if you demand that each pixel be a discrete, independently-addressable unit capable of expressing a full range of color, then the current crop of RGBW LCDs doesn't cut it.

If the limitations of RGBW LCDs were restricted to test patterns, perhaps you could argue that it might not matter to many consumers whether it's a "true" UHD display or not. But I found that the sub-pixel scheme used by RGBW LCDs can impact some content. While cable TV looks essentially the same on RGB and RGBW LCDs, in other scenarios, I spotted clearly identifiable differences in how details were rendered. For example, when viewing slideshows of high-resolution aerial golf-course images, I noticed anomalies in how the greenery was rendered—it was harder to see leaf and grass blade patterns on the RGBW display—and often golf balls appeared to be stretched-out horizontally, making them resemble divots.

I tried switching the TVs in and out of PC (4:4:4) mode. On the RGB panels, I saw no difference in detail rendition with the golf photos. However, the LG's detail rendition did improve quite a bit in PC mode. It did not achieve the resolution of the RGB panels, but it came close. The real issues arose when the LG was not in PC mode—that's when I saw clearly visible loss of detail when compared to the other TVs.


Photo of the Samsung JU7100F RGB LCD's screen.


Photo of the LG UH6150's RGBW LCD screen. Note how the golf balls don't look like golf balls.

I did not see a similar effect on any other display I own, whether it was a TV, laptop, tablet, or phone. Only the LG RGBW LCD with shared white sub-pixels struggled to faithfully render the organic textures in those photos.

What I noticed in those golf shots is highly relevant given that, just a few days ago, The Masters was broadcast in UHD/4K resolution, a first for a live sporting event in the US. With ultra high-definition golf, you want to be able to tell divots apart from golf balls, otherwise what's the point? The RGBW display added ambiguity that was not present with the RGB displays.

Another issue I noticed during my testing pertains to color luminance. The issue here is elementary—RGBW TVs can't achieve their maximum peak luminance without the help of the white sub-pixels. That's great if you watch ice hockey or skiing all the time, but not ideal for content that's full of rich, saturated colors. It's hard to make a judgement call on how severely color-starved highlights affect total image quality, but it exists as an issue in parallel to the chroma (color) resolution limitation of RGBW LCD.

The conundrum lies in how much to care about RGBW LCD's shortfalls. If you only lost a bit of chroma resolution, I would say it was no concern. If RGB and RGBW LCDs looked essentially identical when playing 4:2:2 or 4:2:0 UHD video and test patterns, I'd say fuggedaboutit. But the reality is more nuanced; in the end, I was able to find visible image-quality degradation caused by the RGBW LCD using both test patterns and real content, and especially when the TV was not in PC mode.

I won't claim that the differences between RGB and RGBW LCD are super-obvious. From 11 feet away and with cable as the source, you won't spot a difference on a 55" TV. Then again, at that distance, you'll never see the full resolution offered by any 55" UHDTV—you may as well buy a 1080p TV and pocket the difference.

If you spend additional money for the extra resolution offered by a UHD/4K TV, and especially one that's identified as a 4K Ultra HD model, that TV should deliver the resolution the CTA logo promises: 3840x2160 pixels. For that matter, in my view, any TV that claims UHD resolution ought to be able to do so without adding qualifiers and conditions to how it gets there. With both real-life content and test patterns, RGB LCDs had no problem hitting the UHD resolution target.

Do you have any experience with LG's RGBW LCDs? If so, please let me know your impressions in the comments.
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post #2 of 45 Old 04-12-2016, 05:54 AM
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Could you add a list of model numbers (to the original post) that use the RGBW pixel structure being discussed? Unless I am mistaken, there are only one or two series at the low end of LG's 4K UHD LED LCD product lineup that use this pixel structure. I think that all of their 2016 Super UHD LED LCD's use an RGB pixel structure. Are there any other manufacturers who use the RGBW pixel structure?
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post #3 of 45 Old 04-12-2016, 06:28 AM
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Nice write up.
Is the CTA reviewing LG's use of the "4K Ultra HD" designation - or are they okay with it? If LG is allowed to claim 4KUltraHD when it appears from your review that it is not, that devalues the logo.
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post #4 of 45 Old 04-12-2016, 06:33 AM - Thread Starter
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Originally Posted by HockeyoAJB View Post
Could you add a list of model numbers (to the original post) that use the RGBW pixel structure being discussed? Unless I am mistaken, there are only one or two series at the low end of LG's 4K UHD LED LCD product lineup that use this pixel structure. I think that all of their 2016 Super UHD LED LCD's use an RGB pixel structure. Are there any other manufacturers who use the RGBW pixel structure?
Good point. Yes, all the LG Super UHD units use RGB LCD panels. The RGBW units are lower-cost LCD models. Since LG does not advertise it as a feature, it is not clear which TVs use this panel type. On LG's website, the RGBW TVs are found under the category called 4K Ultra HD, which happens to also include its OLEDs.

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Good point. Yes, all the LG Super UHD units use RGB LCD panels. The RGBW units are lower-cost LCD models. Since LG does not advertise it as a feature, it is not clear which TVs use this panel type. On LG's website, the RGBW TVs are found under the category called 4K Ultra HD, which happens to also include its OLEDs.


Sony reps took had some negative things to say at CES about LG using RGBW oleds. Sony won't manufacturer an oled that uses that structure.
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Sony reps took had some negative things to say at CES about LG using RGBW oleds. Sony won't manufacturer an oled that uses that structure.
Sure, but LGs 4K Ultra HD RGBW OLEDs still have a discrete sub-pixel group (four sub-pixels instead of the three found in RGB OLED) for each and every addressable pixel in the grid, meaning it can render full 3840x2160 luma and chroma resolution, unlike LG's RGBW LCDs.

Sony's OLEDs happen to be a bit pricey, but because they are used for mastering they cannot sacrifice color saturation for brightness, which is an inevitability with RGBW panels of any type (and is also the case with RGBW DLP projection).
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post #8 of 45 Old 04-12-2016, 08:38 AM
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This is a good explanation of a fairly confusing topic.


But I have to say: I wasn't excited about 4k at TV sizes and now that I've added a projector and 100" screen to my setup I'm even less excited about 4k. I know 4k is now the defacto standard so it's not really a discussion anymore of whether or not it's worth it or not over a 1080p LCD but I guess my question would be how much will this really affect consumers as the only real way to see this type of artifact is to sit unnaturally close to the screen?
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post #9 of 45 Old 04-12-2016, 08:50 AM - Thread Starter
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Originally Posted by sage11x View Post
This is a good explanation of a fairly confusing topic.


But I have to say: I wasn't excited about 4k at TV sizes and now that I've added a projector and 100" screen to my setup I'm even less excited about 4k. I know 4k is now the defacto standard so it's not really a discussion anymore of whether or not it's worth it or not over a 1080p LCD but I guess my question would be how much will this really affect consumers as the only real way to see this type of artifact is to sit unnaturally close to the screen?
I concur, a well mastered Blu-ray shown on a 100” plus screen in a dark room provides a ton of immersion and viewer satisfaction.
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post #10 of 45 Old 04-12-2016, 08:54 AM
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Sure, but LGs 4K Ultra HD RGBW OLEDs still have a discrete sub-pixel group (four sub-pixels instead of the three found in RGB OLED) for each and every addressable pixel in the grid, meaning it can render full 3840x2160 luma and chroma resolution, unlike LG's RGBW LCDs.

Sony's OLEDs happen to be a bit pricey, but because they are used for mastering they cannot sacrifice color saturation for brightness, which is an inevitability with RGBW panels of any type (and is also the case with RGBW DLP projection).
Well isn't LG's implementation of OLED different from Samsung's and Sony's altogether? My understanding is that it isn't just the addition of a white sub pixel but the fact that all of LG's sub pixels are white and simply use color filters for RGB. In this way they could avoid the uneven aging that actual red green and blue OLED sub pixels experience that can cause a display to drift over time.

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Well isn't LG's implementation of OLED different from Samsung's and Sony's altogether? My understanding is that it isn't just the addition of a white sub pixel but the fact that all of LG's sub pixels are white and simply use color filters for RGB. In this way they could avoid the uneven aging that actual red green and blue OLED sub pixels experience that can cause a display to drift over time.
With LG's OLEDs, every pixel consists of a group of independently-addressable sub-pixels that come in red, green, blue, and white. Yes how LG does it is different than how the other guys do OLED, but it still has the characteristics required to render that 1-pixel checkerboard pattern accurately.
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Well isn't LG's implementation of OLED different from Samsung's and Sony's altogether? My understanding is that it isn't just the addition of a white sub pixel but the fact that all of LG's sub pixels are white and simply use color filters for RGB. In this way they could avoid the uneven aging that actual red green and blue OLED sub pixels experience that can cause a display to drift over time.
And I am pretty sure the yields are much better using LGs method, and it also the reason they are the only makes making OLEDs. The others cannot compete with the price of their RGBW method that they have a patent on.
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This whole discussion, while interesting technically, seems less relevant than other UHD 'slight of hand' technology such as the JVC 'fauxK' projectors and maybe even the new 'oscillating mirror' DLP projector chip. Granted, LG has the legal problem of claiming the RGBW sets are 'UHD' but the potential consumer real-world issue is probably much less noticable at normal viewing distance whereas the impact of other pixel slight of hand is likely more noticable for projector products where size-to-viewing distance ratio is much greater. I haven't been closely following those solutions and to what degree they make pseudo-4K claims. I do recall a thread that suggested that JVC fauxK units did some test patterns better than the Sony 4k units yet I think the consensus is that in real world use the Sony's have better resolution (although with slightly worse black levels). I know AVS tries to be 'evidence-based' but maybe this is 'mountain out of a mole hill' scenario

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This whole discussion, while interesting technically, seems less relevant than other UHD 'slight of hand' technology such as the JVC 'fauxK' projectors and maybe even the new 'oscillating mirror' DLP projector chip. Granted, LG has the legal problem of claiming the RGBW sets are 'UHD' but the potential consumer real-world issue is probably much less noticable at normal viewing distance whereas the impact of other pixel slight of hand is likely more noticable for projector products where size-to-viewing distance ratio is much greater. I haven't been closely following those solutions and to what degree they make pseudo-4K claims. I do recall a thread that suggested that JVC fauxK units did some test patterns better than the Sony 4k units yet I think the consensus is that in real world use the Sony's have better resolution (although with slightly worse black levels). I know AVS tries to be 'evidence-based' but maybe this is 'mountain out of a mole hill' scenario
It really depends on your intended use, viewing habits, acuity of your vision and budget whether you should care.
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Originally Posted by IanR View Post
This whole discussion, while interesting technically, seems less relevant than other UHD 'slight of hand' technology such as the JVC 'fauxK' projectors and maybe even the new 'oscillating mirror' DLP projector chip. Granted, LG has the legal problem of claiming the RGBW sets are 'UHD' but the potential consumer real-world issue is probably much less noticable at normal viewing distance whereas the impact of other pixel slight of hand is likely more noticable for projector products where size-to-viewing distance ratio is much greater. I haven't been closely following those solutions and to what degree they make pseudo-4K claims. I do recall a thread that suggested that JVC fauxK units did some test patterns better than the Sony 4k units yet I think the consensus is that in real world use the Sony's have better resolution (although with slightly worse black levels). I know AVS tries to be 'evidence-based' but maybe this is 'mountain out of a mole hill' scenario
It's an issue if you have true UHD resolution content with periodic structures (i.e. mesh, plaid fabric, etc…). The behavior that imagic has described seeing in test patterns can present itself in natural video and would be visible at any distance if moire is introducing an overall color shift at a lower spatial frequency. The only way to eliminate moire is to apply some form of low-pass filtering to the image, which will drop the effective resolution to below UHD.
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Glad to know, I took RGBW panels off of my future shopping list.
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Funny ,actual liquid crystal proponents/researchers want to do away with subpixels using temporal color and blue phase mode , then on the commercial side there is this dodgy , getting-away-with-stuff subpixel mess.

Heck, LG almost got away with the temporal smeared ,even/odd line-by-line polarized passive 3d as full resolution, retarder™ technology.

http://www.theregister.co.uk/2012/02...r_3d_tv_specs/

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Mark, great article.

I don't think there can be any debate as to the fact that these are not UHD resolution displays. The colored stripes and other aliasing in the black/white/black/white pixel pattern makes that quite clear.

The question is, if they're not Full UHD, then what are they? The jury's still out on that.

BTW, although I wouldn't buy a panel using this setup for myself (and absolutely wouldn't consider it for professional use), I don't think that it's a bad product. Using a clear subpixel has its benefits (efficiency/power consumption etc). My concern is that the resolution limitation hasn't been adequately disclosed to consumers.
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the resolution loss is comparable to chroma sub sampling. no vizio can do 4:4:4 and for some reason that doesn't matter a lot to most user.
the difference is that a normal screen upscales chroma and this RGBW screen has to do "something else".

the "fact" that it doesn't look "ok" sounds like yet another problem with LG processing.

in the end i would never buy such a screen. but i would never buy a screen that can't do 4:4:4 in the first place.

these screens are IPS so not the target for videophile people anyway.
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the resolution loss is comparable to chroma sub sampling. no vizio can do 4:4:4 and for some reason that doesn't matter a lot to most user.
the difference is that a normal screen upscales chroma and this RGBW screen has to do "something else".

the "fact" that it doesn't look "ok" sounds like yet another problem with LG processing.

in the end i would never buy such a screen. but i would never buy a screen that can't do 4:4:4 in the first place.

these screens are IPS so not the target for videophile people anyway.
I did alot od reading on Herę and and other forums, and concluded a VA panel was my only option for a quality picture. Well after two weeks with a panasonic cx800 series, and its ATROCIOUS viewing angles , i returned it, andwent shopping for what actually looked good to me. I now have a LG UF65770v, superior viewing angle, contrast and colour. If i only took online opinion AS fact, i would be tolerating an inferior picture. So i always wonder if the IPS doubters have ever tried one! I never buy off reviews alone now
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One thing they should start discussing is the number of zones. VIZIO R65 has 384 zones, which is nice. the LG has over 6-million zones since each pixel is its own zone on an OLED. They should also discuss quality of zones. The Samsung has pretty severe blooming. VIZIO has virtually none.

If I were buying a display today, it would be the 2016 LG OLED.

At the office we have a 2015 and 2016 LG OLED, Samsung JS9500, VIZIO R65 and one of their new 2016 55" P series. Also have 2016 Panasonic HDR capable LCD.
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post #23 of 45 Old 04-15-2016, 04:07 AM - Thread Starter
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One thing they should start discussing is the number of zones. VIZIO R65 has 384 zones, which is nice. the LG has over 6-million zones since each pixel is its own zone on an OLED. They should also discuss quality of zones. The Samsung has pretty severe blooming. VIZIO has virtually none.

If I were buying a display today, it would be the 2016 LG OLED.

At the office we have a 2015 and 2016 LG OLED, Samsung JS9500, VIZIO R65 and one of their new 2016 55" P series. Also have 2016 Panasonic HDR capable LCD.
There's not much to discuss when it comes to zones and edgelit TVs.

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post #24 of 45 Old 04-15-2016, 12:20 PM
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Quote:
Originally Posted by Robert Bays View Post
I did alot od reading on Herę and and other forums, and concluded a VA panel was my only option for a quality picture. Well after two weeks with a panasonic cx800 series, and its ATROCIOUS viewing angles , i returned it, andwent shopping for what actually looked good to me. I now have a LG UF65770v, superior viewing angle, contrast and colour. If i only took online opinion AS fact, i would be tolerating an inferior picture. So i always wonder if the IPS doubters have ever tried one! I never buy off reviews alone now
I have an LG with the S-IPS panel and two Samsungs with the S-PVA panels. The off-axis viewing of the LG panel is remarkable. Both Samsung panels suck as far as off-axis viewing goes. However, the blacks are better with the S-PVA than the LG's S-IPS panel so there are compromises. The LG is our primary tv so it's calibrated (properly) and with the use of a bias light, we've been able to mitigate the less-than-black issue somewhat. PQ is great. No panel is perfect so you pick your poison.
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post #25 of 45 Old 04-15-2016, 01:24 PM
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I'm with Otto on this one as I have a Westinghouse TX-47f430s w/ LG-Philips boards S-IPS panel as well as a Samsung 55' sporting the S-PVA. Both are very good off angle, comparing it to the god awful Samsung SVA.

Quote:
Originally Posted by Robert Bays View Post
I did alot od reading on Herę and and other forums, and concluded a VA panel was my only option for a quality picture. Well after two weeks with a panasonic cx800 series, and its ATROCIOUS viewing angles , i returned it, andwent shopping for what actually looked good to me. I now have a LG UF65770v, superior viewing angle, contrast and colour. If i only took online opinion AS fact, i would be tolerating an inferior picture. So i always wonder if the IPS doubters have ever tried one! I never buy off reviews alone now
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post #26 of 45 Old 04-16-2016, 09:19 AM
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Quote:
Originally Posted by imagic View Post
Good point. Yes, all the LG Super UHD units use RGB LCD panels. The RGBW units are lower-cost LCD models. Since LG does not advertise it as a feature, it is not clear which TVs use this panel type. On LG's website, the RGBW TVs are found under the category called 4K Ultra HD, which happens to also include its OLEDs.
to clarify OLED's have this functionality as well? If so, does this also mean they "suffer" from the same symptoms?
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post #27 of 45 Old 04-16-2016, 10:24 AM - Thread Starter
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Quote:
Originally Posted by tjcinnamon View Post
to clarify OLED's have this functionality as well? If so, does this also mean they "suffer" from the same symptoms?
I addressed RGBW OLEDs in the originaln post.

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post #28 of 45 Old 04-16-2016, 12:10 PM
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I am the person who called the question of lower resolution of RGBw panels to Scott Wilkinson in the tech TV chat. I originally came across RGBw panels when I was reading reviews on a Sceptre U500CV-U 49" 4K Ultra HD 60Hz Class LED HDTV
TV I purchased during Christmas for $350. In the comments people were talking about this TV having a RGBw panel so I did my research to find out what it was. I gave my findings to Scott so he could look into it. I am glad one of the staff did a write up on the issue. I haven't had the chance to delve into the nuances in that TV we purchased. I think the question should be whether or not this is a cost-cutting measure. I cannot confirm that this TV is a RGBw panel. But it certainly seems that if it is and the price is so cheap it might be a pricing issue for manufacturers. Samsung even did a write up on their website in regards to RGBw versus RGB panels. It would be nice to get a list of manufacturers who do this so consumers can be aware of what's going on.

I don't have enough post to add links but if you just google "RGBw TV" you will see the Samsung write up as well as a YouTube video explaining it.

Thanks again for doing the right up!

James
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post #29 of 45 Old 04-18-2016, 05:35 AM
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the bad in WRGB OLED / LED :

1. No calibration disc for RGBW only RGB
2. UPSCALE worse on RGBW lg
3. Viewing screen WRGB through computer this not good upscale ( video card is only RGB )
4. black colors no shades, no details on WRGB ( ips like OLED )
5. no video card on WRGB no movis on WRGB no Tv on WRGB transmission quality decreases on HDMI
6.No color depth
7. You can not adjust white on video card or oppo 103
8. many problems in OLED screen with sharp as in IPS LED lg
9. lg brought option called "Super Resolution" is brings Pixelation
10. Internet connection with a computer picture looks bad

the good :

1. 3D look good / 2D to 3D look good
2.many colors but without depth in the colors ( like samsung )
3. Blu-ray movies via USB after calibration screen can show good movies
4. iptv 1080P + via Internet cable can show Good image with dream Contras
5. only via USB can be conversion 8 bit to 10 bit

very disappointed
i saw RGB OLED Samsung in 2013
still better than LG's screen in 2016
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post #30 of 45 Old 04-18-2016, 07:35 AM
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So basically they sabotaged the "cheap" 4K TV for PC users market. Best Buy must be loving the returns on their house brand TV using this panel type.
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