I work at an advanced materials company called Nanosys that manufactures Quantum Dots for displays. In my work the display business, I’ve noticed a lot of confusion around color science and image quality.
I’ve started this blog as a way to get to the bottom of some of this stuff and share what I’ve learned. My aim is to synthesize information I’ve accumulated in order to provide a useful way for us to understand why great color is so important and exciting.
Watching the latest superhero movie release – loaded with CGI and eye-melting explosions – is obviously a great way to test the cinematic benefits of High Dynamic Range (HDR) and Wide Color Gamut (WCG) formats on your brand-new TV. But what about the many thousands of films from the first hundred-plus years of cinema?
Well, it turns out that one of the earliest full color films ever produced contains a rich range of colors that audiences have not been able see since the original screening of the film in theaters over 80 years ago.
Barry Goch, writing for postPerspective on Warner’s recent 4K HDR restoration of 1939’s multi-Oscar-winning classic, The Wizard of Oz:
George Feltenstein, SVP of theatrical catalog marketing for Warner Bros. Home Entertainment, spoke about why the film was chosen for restoration. “The Wizard of Oz is among the crown jewels that we hold,” he said. “We wanted to embrace the new 4K HDR technology, but nobody’s ever released a film that old using this technology. HDR, or high dynamic range, has a color range that is wider than anything that’s come before it. There are colors [in The Wizard of Oz] that were never reproducible before, so what better a film to represent that color?” (emphasis added)
This is a fantastic use of HDR and WCG technologies. Many classic films have been restored multiple times in recent decades as new formats arose from laser disc to DVD to Blu Ray and so on. Each subsequent release brought improvements in image quality and fidelity but the color reproduction has never really been close to that of the original film. Until now.
Color Gamut of Print Film and modern Digital Camera Sensors compared to the DCI-P3 and BT.2020 standards in CIE1931*. Data source: Sony
Many color movies from the 1930’s, 40’s and 50’s were filmed with rich, vibrant colors. In fact, many popular film-stocks could reproduce a wider color gamut than even the best-performing HDR TVs on the market today. Technologies like Technicolor’s insane Three Strip Process enabled cinematographers to capture and reproduce a range of colors that may have been closer to BT.2020 than DCI-P3.
Brilliant red fireball in The Wizard of Oz
The Wizard of Oz, presents a vibrant, fantastical world containing colors across the spectrum from the famous ruby red slippers to the Yellow Brick Road, the Emerald City and even the occasional bright red fireball. It is therefore a perfect fit for remastering in wide color gamut.
But it is by no means the only older film worthy of this treatment. There are quite a few movies, such as An American in Paris (1951), Singing in the Rain (1952) and countless early Disney animation films that relied on the Technicolor three strip process to create richly colorful worlds. I look forward to seeing more restorations of these classic films that bring back colors that haven’t seen in many decades and that many audiences (anyone under ~90) have never had the chance to see.
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*: Why CIE 1931? Haven’t most people (including me!) moved on from this ancient color space in favor of the far more uniform CIE 1976 or u’v’ color space? Recent work by Dr. Kenichiro Masaoka (the guy who invented BT.2020) suggests that good old CIE 1931 may actually be more useful for making color volume comparisons. Recommend reading his recent JSID paper from 2019 “Color Gamut of Multi‐Chromatic Displays” for more detail: https://doi.org/10.1002/sdtp.13058
After much internet searching and a few cancelled deliveries we finally have our Croatia jersey! A bit too late for the big game but still thought it would be interesting to take a look at the data for both team jerseys:
France vs Croatia jerseys in a 2018 World Cup-themed chromaticity shootout
Like France, Croatia’s jersey happens to fall just inside the BT.709 color gamut. Going back to our original top 10 teams post, it seems like most of the other possible finals matchups would have resulted in a wider color gamut (we did model the Croatian flag red as outside 709).
An interesting follow-up, perhaps for 2022, would be to look at goalie jerseys as well. Goalies wore some of the wildest colors of the competition. France’s Hugo Lorris, for example, wore a super saturated yellow-green for the final match that looked a bit like the tennis ball color we measured recently.
A few weeks ago I kicked off the World Cup with a survey of the top 10 ranked country’s colors. At the time, it was impractical to acquire and measure actual jerseys for each World Cup team (32 total) so I limited the survey to top 10 teams and used publicly available data on flag colors under the assumption that jerseys would likely track closely with flags.
We’re now down to just two teams so, as promised, I’m back to share some measured data from team jerseys. There is, however, a small issue… Croatia jerseys are sold out everywhere! Probably because it is the first time Croatia has entered the World Cup finals. Luckily, I’ve got one on back-order and will follow-up with yet another update next week, after the big game.
In the meantime, let’s take a quick look at the measured data we do have for France.
France World Cup 2018 Jersey Colors plotted in CIE 1931
The plot above shows u’v’ coordinates for the three most interesting colors on France’s World Cup jersey: dark blue, light blue and the small pop of red from the back of the collar. As you can see in the plot above these colors actually fall just inside the BT.709 color gamut used for HDTV broadcast. They’re right on the edge though so, if you are watching in HD, you may want to look at having your TV calibrated before the big game for an optimal experience.
The other question that I had after the first post was whether or not the flag data would truly correlate to measured jerseys. In the chart below, I’ve plotted flag data from the original post against new measured data and it seems like my hypothesis held up. At least in the case of France, team colors were reasonably close to flag colors.
Looking forward to providing an update next week on Croatia’s bright red home jersey. In the meantime, may the best team win!
It’s likely to make a big difference. The World Cup is one of the most colorful sporting events on TV with teams from 32 countries, thousands of flag-waving fans and, of course, wildly colorful cleats.
Color gamut of the 2018 World Cup’s top 10 countries.
With a mix of publicly available data and a little math, I was able to plot the dominant flag colors for the top 10 World Cup countries into the CIE 1931 color space (if you are new to reading color space charts, check out our primer here). Note that I limited the survey to flag colors since data on 2018 uniforms was incomplete and flag colors seem to be featured on most uniforms. I’ve also only plotted the two most dominant or most ‘colorful’ colors, ignoring blacks, whites and grays.
The results were a little bit surprising. Based on this data, just two teams entire flags – Argentina and France – can be accurately displayed on a standard HDTV with the BT.709 color gamut. This means fans with wide color gamut sets will finally be able to see their county’s colors in their full glory when viewing a 4K HDR broadcast.
It’s a great example of the power of HDR and wide color gamut to deliver a lifelike experience that really makes you feel like you are there in the stands in Russia sitting next to a crazy face-painted super-fan waving a flag in support of his country (only without the obstructed view from that flag).
How to watch the World Cup in 4K HDR
If you have a 4K HDR-capable set, the World Cup is available to watch in 4K HDR from a variety of sources around the world this year. Here in the US, TV maker Hisense is making 4K HDR games available for streaming in a partnership with Fox while DirecTV, DISH and Comcast are all offering broadcast options.
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.
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.
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”.
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.
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:
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).
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.
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.
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!
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
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 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.
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.