How much color gamut do displays really need? Part 2: How we perceive color

Jul 16, 2013
Author: Jeff Yurek

Last week I set out to define the ultimate consumer display experience in terms of color performance. I laid out some potential color performance design goals for an ideal display, suggesting that such a display should be both accurate and capable of creating an exciting, immersive experience that jumps off the shelf at retail. Can we achieve both goals? To find out, let's start by looking at how we perceive color.

Color Perception

The color of objects that our eyes see in nature is determined by three things: physical, physiological and psychological:

The color of objects that our eyes see in nature is determined by three things: physical, physiological and psychological.

The physical component of our color perception is a constant based on the laws of nature. It is a combination of the quality of the illumination or light source, in this case meaning spectrum it contains, and the reflectance of the object. In the image above, the ball appears red to the eye because it is reflecting red light, while absorbing most the other colors from the light source.

The physiological part of our vision is also a relative constant that is based on the electrochemical processes of the eye. The back of the retina contains photoreceptor nerve cells which transform incoming light into electrical impulses. These electrical impulses are sent to the optic nerve of the eye and onto the brain, which processes and creates the image we see. And that’s where the psychological component comes in.

Let’s look at how each of these components might affect display color performance, starting with the physical, which ought to be something we can measure.

Physical

Fortunately, a guy named Pointer has done this for us. For his 1980 publication, Pointer measured over 4,000 samples and was able to define a color gamut of real surface colors, of objects found in nature. The result is commonly called “Pointer’s Gamut:"

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

This already seems like a great place to start. It immediately looks like a great fit our first ultimate color experience criteria which was accuracy. If we could accurately capture and reproduce all of the colors found in the natural world it would make for a much improved, more accurate ecommerce experience, for example.

But how important are those extra colors? Looking at Pointer’s gamut mapped against the color gamut of the latest iPhone in the chart above, you have to wonder if we really come across these deep cyans and reds in everyday life. Are they just infrequent, rare colors or something worth pursuing for our display?

Turns out we do. As an example, Pantone’s color of the year for 2012 was a deep emerald green that falls outside of both the iPhone's gamut and the HDTV broadcast standard. This is an important and popular color that appears a bit too yellowish on your computer monitor when you are shopping for the perfect tie on Amazon. So there are some really important colors outside of what the iPhone can display today.

But, what about our second criteria, the lifelike, exciting, immersive experience we want to give consumers? Is the gamut of the natural world enough?

Physiological

If we look at the second component of the visual system, the physiological component, we’ll see that we can actually perceive a much wider range of colors. The cells in the back of retina can actually detect the entire range of the CIE diagram. That’s almost double the range of colors that Pointer found in nature:

Color gamut of the average human eye vs gamut of colors found in nature as measured by Pointer

This is starting to sound like a much more immersive experience. Maybe we ought to pursue the full color capability of the human eye just like the industry has done for high, "retina" resolutions.

It sounds great but it would be a tall order. It would take quite a lot of power, brightness and extra bit depth to even begin to think about covering a color space this large. There certainly would be a high price to pay in terms of design tradeoffs to get there. So are there any truly valuable colors contained in that extra space, similar to the Pantone color in Pointer’s gamut, that would make us want to go for it?

Psychological

This is where the psychological component comes into play.

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 the light that comes out of our retinas.

This may seem hard to believe but this fun demo created by neuroscientist Beau Lotto does a great job of showing just how much our brains actively interpret and change what we see.

Monet's The Poppy Field, near Argenteuil

The color of the chips has not changed in the video above, just our perception of the color. What’s happening here is our experience is telling us that the color chip in shadow must actually be a much brighter color than the chip under direct illumination, so our brain is just making the correction for us on the fly.

Artists absolutely play on this psychological element of our perception of color, sometimes using totally unrealistic or hyper real colors to make us feel or experience something new or help tell a story. In fact, one of the most influential art instructors of the 20th century, Josef Albers, once said that, "the purpose of art is not to represent nature but instead to re-present it."

Monet's The Poppy Field, near Argenteuil

So, whether it’s Monet using saturated and contrasting colors with equal luminance to trick our brains into seeing poppy flowers sway in an imaginary breeze in a 19th century painting or modern films which sometimes rely on the wider gamut capabilities of color film and digital cinema projection to create uniquely cinematic experiences for audiences.

Movies like “The Ring," for example, which used a deep cyan cast throughout much of the film to create tension and help tell a scary story. Or Michael Bay’s "Transformers" movies, which use deeply saturated oranges, reds and teal greens to create an exciting, eye-popping palette appropriate for a summer blockbuster sci-fi movie about giant robots:

Wide color gamut in movies

There’s certainly a place for wild, unexpected colors in art. But, as we go through some of these examples, I think we’ll actually find that there is a huge range of expression possible within the gamut of surface colors that Pointer measured. The full range of gamut detectable by the human eye, while exciting to think about, is not really necessary to deliver both accurate and pleasing (engaging) color to our visual system.

So where does that leave us?

In my next post I'll look at existing wide color gamut standards and content delivery mechanisms to see both what we can do today and what's next for wide color gamut displays.