This is a great, exhaustive tutorial on managing color gamut for photographers by color expert Andrew Rodney. He does a great job making the case for working in wide gamut color spaces like Pro Photo, especially when capturing in RAW. Using smaller gamuts like sRGB throws away useful color data that printers and more and more displays can recreate.
We typically focus on color as it relates to displays here at dot-color, but I came across a fascinating post about color in the print industry from John the Math Guy that I had to share. In this post, John takes a close look at how ink looks at different thicknesses and uncovers the reasons for some seemingly unconventional color-naming habits in the print industry.
What happens when we double the amount of ink on the paper? …it would seem that the thick layer of magenta is a lot closer to red. The plot below shows the actual spectra of two magenta patches, one at a larger ink film thickness than the other. The plot leads one to the same impression – that a thick layer of magenta is closer to red in hue than a thin layer.
Read the whole thing here: http://johnthemathguy.blogspot.com/2012/09/why-does-my-cyan-have-blues.html
Ken Werner of Display Central has a post comparing the benefits of quantum dots to OLEDs in consumer TV applications. Being the authority on quantum dot displays that we are here at Nanosys, Ken contacted us for an analysis. Here is the explanation our Ph.Ds gave Ken:
OLEDs use organometalic compounds to emit light. They typically have a central metal atom surrounded by organic ligands. The decay issues are the same as with typical organic fluorophores. In the excited state these molecules are very reactive to H2O and O2, as well as other small molecules that may be around. Once they react they become a different molecule and they will no longer fluoresce or phosphoresce and give off light. The more blue the light emission, the higher the energy of the excited state, and the more reactive the excited molecule will be. So your blue organic phosphores will have a much shorter lifetime than will red phosphores. The burn-in problem seen in OLED displays, that can be seen after just several weeks of operation with static content, is a manifestation of early blue degradation compared to green and red.
Conventional phosphores like YAG are doped materials. YAG used in white LEDs is actually cerium doped YAG. The cerium atom emits the yellow light and is surrounded by a vast amount of YAG. Quantum dots are similar in that a central core crystalline semiconductor material is used to confine the holes and electrons of the exciton (analogous to the cerium in YAG), and in our material this is surrounded by a thick shell of a different, lattice-matched semiconductor material (analogous to the YAG.) We call this a core-shell Quantum Dot structure. If the lifetime of our materials is less than that of conventional phosphors, it is typically because we have not made a perfectly lattice-matched shell, which may distort the core and cause defects at the core/shell interface that reduces the quantum yield.
The big difference here is that a perfectly made core-shell quantum dot does not have an intrinsic lifetime failure mechanism, whereas the organometallic compounds are intrinsically reactive to their environment, which makes them prone to shorter lifetimes especially at higher energies such as blue.
This is an important discussion, because TVs are a harsh environment for display components, running much hotter and brighter than tablets or mobile phones. You can read the entire post here: http://www.display-central.com/flat-panel/is-quantum-dot-lifetime-good-enough-for-tv/
Commenter William thankfully double checked our math and we’ve corrected a small error in our % NTSC calculation.
We finally got our hands on an iPhone 5 yesterday. I tried asking Siri if she really has 44% more color saturation but she wouldn’t give up the goods, so I went with plan B and aimed our PR-655 spectroradiometer at the phone to find out just how impressive the screen really is. A lot has already been written about this display, but not much empirical evidence has been published about the color performance. How does the screen actually stack up to the marketing claims?
In short, Apple did an exceptional job improving color saturation and display quality in general, but the unit we measured just missed the 44% more color saturation claim.
The 44% more color claim for the iPhone 5 is the same claim Apple made for the new iPad. As with the iPad, increasing the color performance of the iPhone 4S by 44% of NTSC 1953 gamut, measured using the CIE 1931 color space, would result in color saturation matching the sRGB color standard. Using these standards as the goal posts, we measured the iPhone 5 at 70% of NTSC 1953 in CIE 1931, a 39% increase from the iPhone 4S, which measured at 50%. That’s 5% less of an improvement than Apple’s 44% claim and just 99% of sRGB (measured against the sRGB primaries).
While 5% less might seem like a big deal, getting to 99% of sRGB is a major feat and will result in tremendously noticeable color improvement in the phone. Additionally, color filters are notoriously difficult to manufacture. Slight variances in performance like this are common and most likely outside the range of a just noticeable difference for the average person.
If you want to know more about NTSC, CIE and sRGB, and why we are using standards from the 1930s, I have written extensively about this issue in the past.
How did they do it?
Much like they did with the new iPad, Apple significantly improved the color filter performance† of the iPhone 5. Based on our experience, this type of improvement typically means that the display requires 20-30% more power to operate at the same brightness. Considering that the display is already a major source battery drain on the phone, this further underscores the engineering effort Apple made to keep battery life about the same as the 4S.
Let’s take a quick look at the changes in each of the red, green and blue color filters, starting with white, which is all three filters turned on:
Looking at the white spectrum of the iPhone 5, we see that the new color filters are very similar to those of the new iPad. Compared to the 4S, the peaks are slightly narrower, which improves color purity. In order to meet sRGB, they also moved to deeper reds and blues.
As with the new iPad, the biggest difference between the 4S and the 5 is in blue. Apple moved the peak to a deeper blue but, more importantly, they narrowed the filter so less green light leaks through. The green leakage causes blue to look a bit “aqua” on the 4S.
Retinal neuroscientist Bryan Jones looked at both displays under his stereo microscope earlier this week. His close-up shots really show off the difference in blue filters.
Apple again chose a slightly deeper wavelength of green which is less yellow and eliminated some of the blue leakage that had been muddying the green on the 4S.
The change here is subtle but as with the other filters, the peak is narrower, deeper in the red and leakage is reduced. One difference worth noting is that, while we are seeing less peak leakage in the red filter, there had been relatively broadband leakage across yellow, green and into blue that has been largely eliminated.
In all, it’s an exceptionally well-calibrated and accurate display for any kind of device, especially a smartphone. Apple has gone to great lengths to design a screen that brings the vibrancy of sRGB to the palm of your hand.
† If you are not familiar with color filters or the inner-workings of LCDs in general this great live teardown by Bill Hammack is well worth watching: http://youtu.be/jiejNAUwcQ8
Display improvements were once again featured at yesterday’s Apple keynote event. The most obvious improvements may have been the larger display and thinner form factor but most interesting to dot-color are the color claims.
Just like the new iPad, Apple claims that the iPhone 5 can display “44% more color saturation.”
Let’s do some simple math to see how the iPhone 5 stacks up against older iPhones and last week’s color performance claim from Motorola.
- iPhone 4S IPS LCD: 50% NTSC color gamut (CIE 1931†)
- iPhone 5 IPS LCD: 50% * 144% = 72% NTSC color gamut (CIE 1931)
- Motorola Droid Razr Maxx HD AMOLED: iPhone 4S (50%) * 185% = 92.5% NTSC (CIE 1931‡)
So Motorola is still king of the fall 2012 smartphone color saturation, based solely on marketing claims. That said, I wouldn’t be surprised if they updated their marketing to say that the Droid Razr Maxx HD offers 28% more color saturation than the iPhone 5 once it hits store shelves in a couple weeks. I plan to measure all of the announced devices to verify these marketing claims, but for now, this is all we have to go with.
Apple also claimed to be able to match the sRGB standard used in TV and movies. With the addition of the iPhone 5, nearly all of Apple’s flagship products (with the exception of the MacBook Air) now meet this standard. This means content should look very consistent across all Apple devices and may open up the possibility for serious content creation apps in iOS.
It also means we’re only just now catching up to an average CRT display from circa 1990, as the sRGB standard is based on the capabilities of phosphor materials used in CRTs. And even still, the new displays are only covering about 35% of the range of colors a human eye can see. There’s still plenty of room for improvement in display color performance (as well as updated content delivery standards, but that is a whole different post). Hopefully if we keep on this kind of pace with display enhancements, next year we’ll start to see a push beyond the limits of last century’s color standards.
† We’re using the long outdated CIE 1931 color space and NTSC 1953 gamut standards here since this is clearly Apple’s reference when they claim 44% more saturation and sRGB coverage. 50% * 1.44 = 72% and 72% of NTSC 1953 gamut in the CIE 1931 color space is also called the sRGB color gamut.
‡ It is not clear which color space Motorola is referencing; we are assuming CIE 1931/NTSC 1953 for ease of comparison.
Over the past couple weeks we’ve seen device manufacturers start to gear up for the holiday season, highlighted by big product announcements from Nokia, Motorola and Amazon. It’s been especially interesting for me to follow how these companies market the most important part of the device – the screen. While pixel per inch still seems important, device makers have moved into more nuanced territory, highlighting deeper features like reduced reflectivity, improved touch sensitivity and color saturation.
Here’s a roundup the most interesting new display features in this holiday’s hottest devices:
Nokia was first up this week with a new crop of Lumia handsets, the 920 and 820. They introduced a slightly larger display for the flagship 920 (now 4.5 inches compared to last year’s 4.3” Lumia 900), touted a new level of touch sensitivity that even works with gloves and claimed 25% more brightness than rival phones. Also of note, they switched from AMOLED to IPS LCD. It’s not yet clear if cost/supply issues or performance drove this switch. It may be that they preferred the brightness and power efficiency of LCD.
Right on the heels of Nokia, Motorola and Google announced a group of new smartphones, led by the Droid Razr Maxx HD. The company described the new Super AMOLED display as having “85% more color saturation than the iPhone 4S, so everything is in lifelike detail.” It’s great to hear them talking about the value of color performance. Hopefully they’ve included some color rendering optimization to artfully take advantage of that extra saturation without overdoing it.
Amazon followed up yesterday with several new devices across their entire Kindle line-up and a surprisingly technical presentation that took a deep dive into the LCD film stack. They showed how a reduced air gap between the touch screen and LCD surface can reduce screen glare, suggesting the new Fire HD has reduced glare by 25%. Also, in a move that’s sure to please LCD film manufacturers like 3M, they discussed the value of better polarizing filters for achieving wider viewing angles without color distortion.
Of course, everyone still compared their products to the now year old iPhone 4S, so it will be interesting to see how these features stack up to whatever Apple introduces next week. We’ll be sure to pick up a few of these devices and run them through their paces to see how the marketing-speak stacks up to real world performance.
Color can have a powerful physiological effect on us. This should come as no surprise to anyone who’s ever been wowed by a Monet or a Rothko. But color can affect us in ways you never imagined. Recent studies suggest that that the color of a uniform can affect the outcome of an Olympic wrestling match and onscreen colors can influence how much you pay for something on eBay.
In one study, researchers found that Olympic wrestlers wearing red won as much as 60% of the time, even against evenly matched opponents (who wore a different color).
Similarly, in a Journal of Consumer Research study on the impact of color on consumers who buy items on auction sites like eBay, authors Rajesh Bagchi and Amar Cheema found that “red background color induces aggression through a feeling of arousal and it increases aggression relative to blue or gray backgrounds. This causes individuals to make higher bids in auctions but lower offers in negotiations.”
Why? The exact mechanism remains a mystery but researchers see some evidence that aggressive colors like red may actually cause a spike in testosterone levels.
I find it particularly fascinating that color choice did not specifically correlate to the price someone paid for an item. Instead, the colors drove more or less aggressive behavior, which lead participants to either seek the best deal possible against a salesperson or to beat out competing bids in an auction.
It got me wondering how retailers might be using color to influence purchasing. A quick survey of some popular online shopping destinations yielded potentially interesting results. Since product background is not always in the control of the retailer, I looked at the “add to cart” areas of three popular online retailers: Apple, Amazon and eBay.
All three employ a lot of blue, a calming color, in their ‘add to cart’ areas. Apple uses a shade of green, another calming color, for the “add to cart” button. Amazon lists the price in a dark red, while Apple uses a lighter shade to accentuate free shipping.
Next time you find yourself shopping either online or brick and mortar, take note of the colors around you – you may be surprised by how far your environment is being manipulated to get you to pay more.
One of the most important pieces of equipment on the Curiosity rover is not a spectrometer or a laser but a color calibration chart. Nothing is simple when you’re sending a robot on a 354 million mile journey into space, but NASA and Bill Nye (yes, the “science guy”) came up with an ingenious solution to calibrate the colors of the onboard cameras.
In order for NASA scientists to be sure that we are seeing “The Red Planet“ in the correct shade of red, they attached red, green and blue color chips to a sundial on the surface of the rover. These reference colors will guarantee the amazing photos we are seeing of the Martian landscape are accurate.
Here is an animated gif of the sundial on the surface of Mars and a close-up shot of it before it left Earth:
Over the weekend I saw this interesting tweet about color gamut and the NFL and I had to find out if it was true:
Could it be that something as simple as an NFL jersey is not within the color gamut of modern HDTVs? I mapped the Broncos team colors onto the CIE 1976 color space along with the HDTV color gamut standard, called rec.709. As you can see, the orange is right on the edge and the blue is indeed outside the gamut.
When we think of high color content, we think of action movies and video games, but this exemplifies how color performance affects everything we see on our TVs, even down to the jersey being worn by our favorite sports team. Luckily high color displays are on their way to fix this problem. As you can see, the Bronco’s colors fall nicely within the much wider DCI-P3 color gamut.
For many who are new to the world of display measurement, the prevalence of two distinct, but often-interchanged color spaces can be a source of confusion. Since my recent post about the color performance of Apple’s new iPad, a number of people have asked about this topic, so I thought it would be worth a closer look.
In the world of displays and color images, there exists a variety of separate standards for mapping color, CIE 1931 and CIE 1976 being the most popular among them. Despite its age, CIE 1931, named for the year of its adoption, remains a well-worn and familiar shorthand throughout the display industry. As a marketer of high color gamut display components, I can tell you from firsthand experience that CIE 1931 is the primary language of our customers. When a customer tells me that their current display “can do 72% of NTSC,” they implicitly mean 72% of NTSC 1953 color gamut as mapped against CIE 1931.
“…we strongly encourage people to abandon the use of the 1931 CIE color diagram for determining the color gamut… The 1976 CIE (u’,v’) color diagram should be used instead. Unfortunately, many continue to use the (x,y) chromaticity values and the 1931 diagram for gamut areas.”
So why are there two standards, and why are we trying to declare one of them obsolete? Let me explain.
What is a color space?
First, a little background on color spaces and how they work.
While there are a number of different types of color spaces, we are specifically interested in chromaticity diagrams, which only measure color quality, independent of other factors like luminance. A color space is a uniform representation of visible light. It maps the all of the colors visible to the human eye onto an x-y grid and assigns them measureable values. This allows us to make uniform measurements and comparisons between colors, and offers certainty that images look the same from display to display when used to create color gamut standards.
In 1931, the Commission internationale de l’éclairage or CIE (International Commission on Illumination in English) defined the most commonly used color space. Here’s a look at the anatomy of the CIE 1931 color space:
What makes a good color space?
An effective color space should map with reasonable accuracy and consistancy to the human perception of color. Content creators want to be sure that the color they see on their display is the same color you see on your display.
This is where the CIE 1931 standard falls apart. Based on the work of David MacAdam in the 1940’s, we learn that the variance in percieved color, when mapped in the CIE 1931 color space, is not linear from color to color. In other words, if you show a group of people the same green, then map what they see against the CIE 1931 color space, they will report seeing a wide decprepancy of different hues of green. However, if you show the same group a blue image, there will be much more agreement on what color blue they are seeing. This uneveness creates problems when trying to make uniform measurements with CIE 1931.
The result of MacAdam’s work is visualized by the MacAdam Elipses. Each elipse represents the range of colors respondents reported seeing when shown a single color, which was the dot in the center of each elipse:
A better standard
It was not until 1976 that the CIE was able to settle on a significantly more linear color space. If we reproduce MacAdam’s work using the new standard, variations in percieve color are minimalized and the MacAdam’s Elipses mapped on a 1976 CIE diagram appear much more evenly sized and circular, as opposed to oblong. This makes color comparisons using CIE 1976 significantly more meaningful.
The difference of the CIE 1976 color space, particularly in blue and green, is immediately apparent. As an example, lets look at the color gamut measurements of the iPad 2 and new iPad we used in an earlier article. Both charts do a reasonably good job of conveying the new iPad’s increased gamut coverage at all three primaries. But, the 1976 chart captures the dramatic perceptual difference in blue (from aqua to deep blue) that you actually see when looking at the displays side by side:
The increased gamut of the new iPad is worth testing. Next time you find yourself in an Apple store, grab an iPad 2, hold it alongside a new iPad, Google up a color bar image and see the difference for yourself.
So, why do we still use CIE 1931 at all? The only real answer is that old habits die hard. The industry has relied on CIE 1931 since its inception, and change is coming slowly.
Fortunately, CIE 1931’s grip is loosening over time. The ICDM’s new measurement standard should eventually force all remaining stragglers to switch over to the more accurate 1976 standard. Until then, you can familiarize yourself with a decent color space conversion calculator, such as the handy converter we built just for this purpose: