Introducing Wide Gamut Wednesdays

This week I’m kicking off a new series of posts that set out to answer a simple question:

“Can an HDTV accurately reproduce these colors?”

I’m calling the new weekly feature “Wide Color Gamut Wednesday” or #WideColorWednesday in social media speak. Each week we will analyze a new wide color gamut image and post the results to our @dot_color Twitter feed.

In the process, I think we’ll find that “wide gamut” colors – colors that fall outside the BT.709 color gamut used by HDTVs – are actually fairly common beyond classic examples like Brazilian tree frogs or Coca Cola cans. In fact, in our first test, we found a simple image of spring flowers, taken in Rochester, NY, contained mostly colors that fall outside the BT.709 gamut.

Wide Color Gamut image analysis

62.5% of the colors in this springtime flowers image fall outside the BT.709 color gamut used by HDTVs #WideGamutWednesday

I thought it would be helpful to write up the first #WideColorWednesday image as a blog post with some background on the process used to create these images.

Continue reading

Are tennis balls yellow or green?

Tennis star Roger Federer’s answer to this seemingly innocuous question via twitter user @delaneyanndold caused a bit of a stir on social media earlier this week. According to Mr. Federer, tennis balls are very definitely yellow. He’s certainly an expert when it comes to tennis but how is his color accuracy? We applied some basic science to answer this important question once and for all. The answer might surprise you…

With his world-record 20 grand slam tennis championships, it’s likely few people on earth have spent more time looking at tennis balls than Roger Federer. He’s also backed up by the International Tennis Federation which has required all tennis balls be “yellow” in color for the last 46 years.

Case closed, team yellow for the win right?

Despite this overwhelming evidence in favor of yellow we still weren’t totally convinced. Reminiscent of the 2015 dress color controversy, Federer’s comment had Twitter users questioning reality. It turns out a large chunk of the population are totally shocked that tennis balls might be considered anything but green.

It’s understandable that Twitter users might be so passionate about this issue. After all, it can be a bit mind bending to think that much of the rest of the world sees such a common object as a completely different color.

So which is it? Are tennis balls green or yellow and, more importantly, why would we see them so differently? We had a hunch there might be more to this story so we set out to settle the debate once and for all with science

Yellow vs Green

Before we answer the question, we need to define the colors yellow and green so we know what we are looking for. There is broad agreement that humans perceive wavelengths of light from 520 to 560 nanometers as “green” and 560 to 590 nanometers as “yellow”.

Spectrum of Green and Yellow

According to our Physics textbook, “Fundamentals of Atmospheric Radiation,” the color green is defined as 520-560nm and yellow as 560nm-590nm.

These two colors are right on top of each other so, right away, it’s easy to see why there might be some confusion here.

Tennis Ball Color Measurement Nanosys

Capturing the spectra of a tennis ball with our Photo Research PR 655

With these wavelength ranges in mind for green and yellow, we grabbed our trusty spectroradiometer, our Wilson* Official US Open tennis ball, and captured some data. What we found when we plotted the data surprised us:

Tennis Ball Spectra

Measurement of light reflected from our tennis ball shows that the color is really green and yellow (or chartreuse). Shaded green and yellow regions represent generally accepted wavelength ranges for those colors.

Our original question turns out to be sort of a trick question. Tennis balls are neither green or yellow, they’re actually both green and yellow!

Looking at the data above, our tennis ball has a definite peak of reflected light at 525nm. 525nm is squarely in the green range but we would expect a pure green to have a bit more defined peak. Since we also see a significant amount of energy in the yellow range, a more accurate description of this tennis ball’s color might be “chartreuse” (link: https://en.wikipedia.org/wiki/Chartreuse_(color)) which lies right between green and yellow.

Why do so many people see tennis balls as either green or yellow?

The colors we see are determined by three things: the physical color of light reflected by an object, the physiological, electrochemical process of the eye to convert that light into an electrical impulse and the psychological, the processing the brain does to create an image from that signal. We already measured the physical component so it’s the last piece, the psychological that we’re most interested in in understanding why we might disagree about an object’s color.

Seeing is not passive. Our brains add meaning to the light that our eyes detect based on context and experience and memory. We are continuously and actively re-visualizing and color-correcting the signal that comes out of our retinas.

One of the ways our collective brains may be influenced is by the appearance of tennis balls on TV. If tennis balls appear more yellow or more green on TV, that could shift our perception of the color. To find out if this might be a factor, we plotted our tennis ball into the CIE 1976 color space so we could compare it to a standard TV color gamut (if you’re not familiar with these charts, check out our primer on chromaticity diagrams).

Tennis ball vs TV Gamut.001

The “color gamut” of a tennis ball, plotted in CIE 1976. Left: tennis ball compared to HDTV BT.709 and UltraHD TV BT.2020 color gamuts; Right: zoomed-in view showing the tennis ball chromaticity is just outside the BT.709 color gamut

Here we see that the tennis ball is a very saturated color that lies right between green and yellow. It’s also interesting that our tennis ball is right on the edge of the BT.709 color gamut used in HDTV broadcast. In fact, if we take a closer look at the zoomed-in chart on the right, the tennis ball is just outside the range of colors used by HDTVs.

Displays cannot simply recreate the exact spectra of light reflected off of a tennis ball that we measured above because displays create color through a totally different process called additive mixing. Displays mix just three primary colors of light (red, green and blue) to recreate millions of colors. In the case of a tennis ball, a display essentially tricks our eyes into seeing chartreuse, by mixing together red and green light. The quality of chartreuse that a display can reproduce is therefore determined by the quality of red and green light a display can reproduce.

Since the tennis ball falls outside the primary colors of the HDTV broadcast signal, this means that the color of a tennis ball is essentially impossible to accurately reproduce on a standard HDTV. Additionally, most HDTVs would not have the correct red and green to recreate our exact shade of chartreuse. As a result, the actual color that most TV viewers experience is based more on the creative decisions of broadcast crews and the color gamut mapping algorithm of their TV, which may be shifting the color more towards yellow.

If that’s the case, it would help explain why so many of us perceive tennis balls as yellow. That’s because they are yellow when they mean the most to us, which is on TV during an important match. This doesn’t quite explain Federer’s perception. Although it is quite possible that he’s watched enough endless hours of film working to improve his game, which he likely cares deeply about, to have shifted his view towards yellow.

It will be interesting to see if our collective tennis ball color perception begins to shift towards green or chartreuse as more and more people adopt UltraHD TVs with wide color gamut capabilities.

*: Note that we chose to use a Wilson ball since it’s the official ball of the US Open and we’re based in the US. As a future experiment, it might be interesting to test the ball used at other events like Wimbledon to see if there’s any international variance in color.

Special thanks to Ernie Lee and Brian Mui!

Watching the World Cup finals this weekend? Your HDTV probably can’t show off Messi’s boots in all their bright blue glory

Lionel Messi laces up some bright blue boots- these super saturated Adidas Sambas were designed for the FIFA World Cup 2014 (image source: Adidas)

Lionel Messi laces up some bright blue boots- these super saturated Adidas Sambas were designed for the FIFA World Cup 2014 (image source: Adidas)

If you’ve been following the FIFA World Cup this summer you may have noticed many players wearing some seriously colorful cleats. These super saturated Sambas are part of a new line-up specially designed by Adidas for the 2014 FIFA World Cup. They are being worn by many of the game’s top players like Argentina’s Lionel Messi who will be wearing his bright blue boots during the finals this weekend.

What you may not know is that, as wild as these shoes appear on your TV, you are actually not getting the whole picture. Today’s HDTV’s are only able to reproduce a limited range of colors- only about a third of what your eye can see- so there’s a lot missing. Common colors from the red of a London bus to Pantone’s color of the year fall outside this small range and watching the games over the past few weeks I’ve been thinking these shoes are also likely to be too colorful for TV.

The horseshoe shaped chart above represents the range of colors that our eyes can see and the triangle contains all the colors an HDTV can show. Lionel Messi's blue cleats fall well outside that range so the color you see on your TV is not accurate.

The horseshoe shaped chart above represents the range of colors that our eyes can see and the triangle contains all the colors an HDTV can show. Lionel Messi’s blue cleats fall well outside that range so the color you see on your TV is not accurate.

So, in honor of this weekend’s World Cup final, I got my hands on a pair of boots that matched my favorite player, Messi’s, and took some measurements to see what I’d find. Turns out that deeply saturated blue falls well outside the range of colors that HDTV’s can produce.

You may not be able to see those blue boots in their full glory unless you are at the stadium but, if the semi-finals are any indication, this weekend’s games should still be pretty exciting to watch!

Is the rec.2020 UHD color broadcast spec really practical?

I’ve often advocated on this blog for Pointer’s Gamut as an important design goal for display makers but is it really practical today from a technology perspective? Pointer’s Gamut covers a huge area and it’s odd shape makes it awfully difficult to cover with just three primaries. Rec.2020, the leading Pointer’s-covering color gamut broadcast standard and de facto standard for upcoming UHD broadcasts, demonstrates this perfectly. It uses very deep red and green primaries to ensure that all those purples and cyans can get squeezed it into the triangle.

rec.2020 needs a very deep green to cover 99.9% of Pointer's Gamut

rec.2020 needs a very deep green to cover 99.9% of Pointer’s Gamut

It’s certainly tough to make a display that can reproduce primary colors that are that saturated and it is especially hard to do so efficienctly. Until now the displays that have come closest rely on an esoteric and power-hungry laser backlight system that can only cover up to about 91% of rec.2020 spec. That is impressive given how ambitious rec.2020 is but a bulky $6,000 laser display doesn’t exactly qualify as practical and it’s certainly not a technology that we are likely to find in a tablet or smartphone anytime soon given it’s low power efficiency.

That may be about to change.

My company, Nanosys, has been working on this problem and we now think it is practical to produce an LED LCD that covers over 97% of rec.2020 using Quantum Dot technology. The latest generation of our Quantum Dots emit light with a very narrow Full Width Half Max (FWHM) spec of below 30 nanometers for both red and green wavelengths. FWHM is pretty obscure spec to be sure but it means that the color is both very pure and accurate. That pin-point accuracy actually enabled us to demonstrate over 91% rec.2020 just by modifying an off-the-shelf, standard LCD TV set with a specially tuned sheet of Quantum Dot Enhancement Film (QDEF).

Nanosys demonstrates over 91% coverage of rec.2020 using Quantum Dots

Nanosys demonstrates over 91% coverage of rec.2020 using Quantum Dots and a standard LCD TV color filter

Very impressive and even a bit better than the performance of that laser TV but still not quite all the way there. What else could be optimized to improve the system and get us closer?

Looking at the spectrum after the color filters revealed a significant amount of blue leaking through the green filter. This leakage was causing the blue point to shift away from the rec.2020 primary. By optimizing the system and selecting a different blue color filter material with a sharper cutoff, Nanosys engineers showed that it is possible to build a display that covers over 97% of the rec.2020 standard– with great power efficiency.

Quantum Dot enhanced displays are in mass production today, they are used in commonly available displays on the market today. Their high power efficiency also means they can be used in all kinds of devices from smartphones to TVs. So, for the first time, it is actually becoming practical to build displays that cover the massive rec.2020 standard and since rec.2020 is part of the UHD broadcast spec this great news for the next generation of 4K and 8K devices.

Pointer’s Gamut follow-up by TFT Central

figure7_Pointer in CIE1976

Last summer I wrote a multi-part series here that looked at how much color gamut displays really need. In those articles I used the gamut of colors found in the natural world, as defined by Pointer, as a possible design goal for an ideal color display. Kid Jansen at TFT Central has followed-up on my piece with a much more detailed look at how several current color gamut standards and devices perform compared to Pointer’s gamut. He’s done some great analysis and it’s well worth reading, check it out here.

CES 2014 Display Wrap-Up

CES 2014 has come to a close and while many predicted a lackluster year, there were actually a number of interesting developments in displays. These are my top three CES 2014 display technology takeaways:

CES 2014 85" Hisense QDTV

4K is here now, content isn’t the issue anymore

Analysts are still having a tough time figuring out exactly how quickly 4K will be adopted. According to data presented by the LCD TV Association at the show, last year analysts thought we’d see about 2 million 4K sets in 2014. Actual numbers turned out to be about 13 million (with 10 million predicted in China alone). 4K is clearly happening faster than most predicted but, if anyone still doubted that 4K will be mainstream in the next couple of years, this year’s CES should have made it clear that its here today.

Just about every major set maker showed off 4K sets this year in every flavor imaginable from LCD to OLED. But, hardware has never been the real barrier to 4K adoption– it’s all about the content or lack thereof. At CES 2014, the content issue was resolved a couple of different ways: Netflix is making 4K delivery a priority and upscaling is starting to look really good. With great upscaling (in one demo I saw from Technicolor it was nearly impossible to pick native 4K from upscaled 1080P) and instantly available content from Netflix, I don’t think content availability will continue to be a barrier for 4K adoption.

Wide Color Gamut and High Dynamic Range

Both Dolby and Technicolor demonstrated some very impressive high dynamic range and wide color gamut technologies that make for much more immersive viewing experiences. With it’s new Dolby Vision technology, Dolby has created essentially a new standard that uses a layer of metadata on top of today’s broadcast standard to deliver wider gamut and dynamic range with the content creator’s intentions intact. This is significant because it won’t require a new broadcast standard. Much like their surround-sound offerings (which deliver stereo audio if you have two speakers and full surround if you have six), all you’ll need is a Dolby-capable set to see the advantages, it won’t be something the viewer has to worry about.

Similarly, Technicolor is doing some on-the-fly processing to incoming content in realtime to pull out extra dynamic range and color. Again, no change in broadcast standard required for this and that’s the key. While there’s some danger that artistic intent will be altered with this approach, the demos I saw looked great. Skin tones and memory colors were kept in check while still taking advantage of the extra saturation offered by a wide color gamut display.

Quantum Dots

One of the most impressive displays at CES 2014 was Hisense’s 85″ 4K wide color gamut Quantum Dot TV. This set promises to bring OLED-like color performance at 4K resolutions to the US market this September at LCD prices (we heard a 55″, 65″ and the 85″ will all be offered). A number of other manufacturers also demonstrated Quantum Dot displays off the main show floor. We saw displays ranging in size from 5″ smartphones, to notebooks to monitors as well as TV’s. 2014 looks to be the year that Quantum Dots gain serious traction in the display market after a strong debut in 2013.

How much color do displays really need? Part 4: Content Delivery

In the previous post in this series, I made the case for displays with hybrid, custom color gamuts as a great way to deliver coverage of Pointer’s gamut as well as the most important broadcast standards. We can build the hardware today to support these large color gamuts so its seems like a great solution but there is a catch: nobody is broadcasting or distributing these large color gamuts today. So, are we going to have to wait for broadcasters and content creators to slowly catchup, much like we did with HDTV?

What content delivery looks like today

Content is captured and viewed in a wide variety of gamuts across a range of different devices but only broadcast in one gamut.

Content is captured and viewed in a wide variety of gamuts across a range of different devices but only broadcast in one gamut.

Today, content creators are actually shooting in a wide variety of color spaces ranging from RAW to rec.709 to Adobe 1998. They are then forced to cram all of these different sources into the lowest common denominator rec.709 standard for broadcast or distribution. That same content is then displayed on devices with a range of different gamut capabilities from tablets that only cover about 70% of rec.709 to HDTVs that do meet the spec to OLED devices that oversaturate the content.

There’s a lot of diversity on both the capture and display sides and a clear bottleneck in the middle in the form of broadcast and distribution channels.

Adhering to broadcast standards is no longer sufficient to guarantee a good experience for consumers because there’s already too much diversity on the display side alone to rely on one standard. You just can’t be sure that consumers are actually looking at your content on a rec.709-capable device. We’re also losing a lot of the value that creators are capturing and could, in many cases, be delivered to end viewers who have the devices to show it.

How do we get around broadcast standards?

What content delivery looks like tomorrow

The first thing to note is that the internet is democratizing broadcast and distribution channels. With the web we can deliver whatever we want, whenever we want. Some players in the industry, notably Sony, are already doing this with 4K content. If there’s no content available and you believe in 4K resolution, you just deliver your own content directly to your customers.

Wide color gamut displays combined with good quality color management and the web as a broadcast platform will allow content to accurately be displayed in the correct color gamut.

Wide color gamut displays combined with good color management and the web as a broadcast platform will allow content to accurately be displayed in the original color gamut.

Still, this leaves us with some potential experience problems. If the right display gamut is not matched to the right content the results will be no different and that’s why color management is key. There are several companies working on color management solutions and certification programs for devices that will make it possible for wide color gamut displays to handle a variety of incoming gamuts. Using metadata, for example, a wide color gamut display can be alerted to the presence of Adobe RGB content and then remap that content on the fly to assure that it is displayed accurately on that specific panel.

With great color management, we can maximize the gamut on the display side and pull through the best possible gamut for the device we are looking at. In this way, we can deliver always accurate content that meets the designers intent, wether artistic or commercial.

Google claims new Nexus 7 delivers 30% wider range of colors – what do they mean?

Google announced an updated version of their Nexus 7 tablet this morning. Central to Google’s pitch was the improved display with both more pixels and more color. The device does feature an impressively high resolution, packing 2.3 million pixels into a 7″ form factor. But, I’m more interested in the color performance and, on this point, Google was vague offering only that the display, “has a 30% wider range of colors.”

What do they mean by that?

It depends on their frame of reference- what color space they are using and what color gamut standard they are comparing against. Since Google talked about the accuracy of HD video at their event, let’s assume that they are referring to the HDTV broadcast standard (rec.709) and using the common CIE 1976 (u’ v’) color space.

When I measured last year’s Nexus 7, I found it could only reproduce about 82%* of the colors found in the rec.709 standard. Color reproduction was not accurate and a little bit undersaturated on this device:

Color gamut of Google's Nexus 7 versus the HDTV broadcast standard (rec.709). Plotted in CIE 1976 (u' v').

Color gamut of Google’s previous generation Nexus 7 versus the HDTV broadcast standard (rec.709). Plotted in CIE 1976 (u’ v’).

With just a simple calculation, increasing 82% by 30%, you’d get about 106% coverage of the HDTV broadcast standard. While that’s actually a slightly wider color gamut than the standard, it is not uncommon for device makers to use a wider color gamut in order to guarantee the color spec across all devices with some room for manufacturing tolerances. This means video and web content should be displayed accurately and it could make for a great looking display.

We’ll order and measure one as soon as they are available to verify so stay tuned…

* note: I always measure coverage of broadcast standards, not simply total area since that can be misleading. However, in this case, coverage and area are nearly the same since the Nexus 7’s gamut is smaller than rec.709.

How much color gamut do displays really need? Part 3: Existing color gamut standards

Last week I looked at the three “P’s” of human color perception– physical, physiological and psychological– as a way to help define a color gamut for the ideal display. Based on real world examples from art and commerce, I concluded that the range of colors found in nature, as measured by Pointer, provided the best fit with our two design goals which were an accurate and exciting, immersive experience.

This week, I’d like to get a little more practical and take a look at existing color gamut standards to see what we might realistically be able to achieve today.

What fits best?

Color gamut of 4,000 surface colors found in nature as measured by Pointer in 1980 against the color gamut of the iPhone 5.

Color gamut of 4,000 surface colors found in nature as measured by Pointer in 1980 against the color gamut of the iPhone 5.

The first thing you’ll notice about Pointer’s gamut (pictured above again) is that it’s a pretty odd, squiggly shape. This means it is going to be difficult to cover efficiently with a three primary system that mixes just red, green and blue to create all the colors we see, like the LCD found in the iPhone. In order to cover Pointer’s with just those three colors, we’d need to make them extremely saturated. There are proposed standards that take this  approach, such as rec.2020, but since they are not practical to implement today from a technology standpoint I’ve decided to ignore them for this discussion.

For the near future, we’ll need to rely on just three colors to get the job done, so what can we do now? Let’s look at two popular wide color gamut standards: Adobe 1998 and DCI-P3:

Current wide color gamut standards Adobe RGB 1998, commonly used by pro photographers and designers, and DCI-P3, used in digital cinema, compared to Pointer's gamut in CIE 1976

Current wide color gamut standards Adobe RGB 1998, commonly used by pro photographers and designers, and DCI-P3, used in digital cinema, compared to Pointer’s gamut in CIE 1976

Let’s start with Adobe 1998. Many people are familiar with this color gamut since it is found as an option on many consumer cameras and it is popular among creative professionals. It certainly covers a significantly wider range of colors than the HDTV broadcast standard with a very deep green point. The rich cyans that we talked about in the movie “The Ring” would look great in Adobe 1998. But, we’re not getting any more of those exciting reds and oranges. In fact, Adobe’s red point is identical to the HDTV broadcast standard.

What about DCI-P3 then? Designed to match the color gamut of color film and used in cinemas all over the world, DCI-P3 has a very wide gamut. The reds are particularly deep and, of course, all of the colors from the movies we looked at are covered. Still, it’s missing a lot of the deep greens found in Adobe 1998 and only just fits the green Pantone color of the year. So DCI-P3 is not quite perfect either.

What about a hybrid, custom gamut? 

What if we combined the green from Adobe with the red from DCI-P3 and their shared blue point? We’d end up with pretty good, high 90’s percentage coverage of Pointer’s gamut, coverage of all of the existing HDTV broadcast content, full coverage of cinema content from Hollywood and a superior ecommerce experience with most of the colors from the natural world covered.

Hybrid color gamut standard that combines the green point from Adobe 1998 with the deep red of DCI-P3

Hybrid color gamut standard that combines the green point from Adobe 1998 with the deep red of DCI-P3

Looks pretty great and we can make displays now that cover this color gamut with today’s technology. But how would it work on the content side? Would we need to get together and agree on this new standard and then wait for years while it is slowly adopted by content creators and display makers?

Next week

Next week we’ll look at how content delivery might evolve to support gamuts like this without the need for major changes to broadcast standards.