Challenges of Achieving Color Accuracy with Commercial Digital Signage

What color are the strawberries in this picture? 

There are two common answers: Some say the strawberries are red, while others think they are grey. How can people look at the same image but see two completely different colors?

Variances in human eye structure – as well as many other factors – can help explain this phenomenon. These factors pose a significant challenge for the advertising industry where color accuracy is critical.

In this article we’ll discuss these challenges and how they affect different types of commercial signage. 



Biological factors affecting color accuracy:



Human Eye Structure

One of the primary factors affecting color accuracy is the structure of our eyes. Within our retinas are three types of photoreceptor cells, called “cones” [2]. Our cones come in three sizes, each size receptive to a specific range of color within the visible spectrum: S cones help us see blue, M cones help us see green, and L cones help us see red. People can be born with fewer, smaller, or defective cones, which affects the way they see certain colors. For example, those who have smaller, defective, or fewer S cones will not be able to see blue as well as those who have more normal S cones[3]. Age plays a role in color accuracy, too. As we age, our eye lens becomes weaker and physically changes the way we see[4]. Human vision can vary quite dramatically depending on the distribution of cones and the age of our eyes. This helps to explain why color can be subjective.

Color Memory

Another factor that affects our color vision, or at least our interpretation of color, is our color memory. If you happen to see red in the above strawberry picture, your color memory is playing tricks on you! Those strawberries do not contain any red pixels, only grey. If you crop a section of the strawberries and look at it separately, you’ll be able to tell there’s no red. But, when we see the picture in its entirety, our memory of strawberries being red makes us perceive that they’re red[5], when, in fact, they’re not.

To maintain color consistency, people developed color standards. The currently established color standards for print and digital media include Pantone, CMYK, and RGB. For video, the color standards are Rec. 709, sRGB, DCI-P3 and Rec. 2020[6]. These standards regulate how much red, green, and blue should be included when reproducing a specific color and are very helpful in terms of reproducing accurate colors for brands’ logos and advertisements.

Now that we understand how some biological factors affect color accuracy, let’s explore how this plays out for commercial signage, both printed and digital.

Challenges of achieving color accuracy with printed commercial signage:

Printed signage is a marketing and advertising tool that’s been used for centuries. When it comes to achieving color accuracy, printed signage presents some unique challenges:

Printable Colors

To print colors accurately, designers must work within a pre-set color space, or range of colors a printer is able to capture or reproduce[7]. CMYK is one of the most popular color spaces used for printing[8], but it does have one disadvantage: CMYK color options are limited to around 16k colors, compared to up to 16.7 million for displays – a factor of 100 times less. So, not all colors are possible to achieve on printed signage[9].

Material Color

Furthermore, printed medium (i.e. paper, vinyl, etc.) itself has color. The material color can change the appearance of the printed color and cause color inaccuracy.

Ink Absorption

Paper and other materials absorb ink during printing. The more absorbent the material, the more difficult it can be to achieve color accuracy as more ink is required to achieve full color saturation. Paper with a glossy coating has low absorption[10], and can be an effective way to achieve color accuracy without using excessive amounts of ink.

Digital signage has one significant advantage over printed signage when it comes to achieving color accuracy: wider color gamut.

Color gamut is defined by the range of colors in the spectrum that human eyes can identify[11]. Within display technologies, like those used in digital signage, color gamut refers to the total range of colors a display can produce. The wider the color gamut rating of a display, the more colors it can produce for viewers.

LED and LCD displays used in digital signage reproduce colors via an RGB color system. Red (R), green (G), and blue (B) pixels are arranged in rows and columns across the display panel. These pixels can be illuminated in numerous combinations to produce a wide color gamut (i.e. range of colors) – much wider than what’s available for printing in CMYK colors. This is one advantage digital signage has over printed signage.

Reflective LCD signage is a relatively new technology for digital signage applications. Reflective LCDs work similarly to other LCDs, except they have a mirror-like/reflective layer installed behind the rear polarizer instead of a backlight. This mirror-like layer illuminates the display using reflected ambient light.



Moreover, for LED digital signage, there is a light output variation which means that increases in temperature adversely affect the color accuracy of emitted light. For example, as LED display temperature increases during extended use, the emitted light will have a red spectrum shift where the display images will have a reddish tone. Not only that, but the increasing temperatures can damage the display hardware. Temperature control solutions, such as cooling fans, can be added to prevent these effects from heat production. However, these mechanisms further increase the bulkiness and power consumption of the display.



Ways to improve the color accuracy of digital signage:

Since reflective color LCDs are illuminated by reflected ambient light (such as the sunlight), they actually improve in image quality and color accuracy the brighter the sun shines – all while using very little power. Among the many other advantages of reflective color LCDs, the absence of a backlight significantly reduces or eliminates the output of additional light "noise", radiation, heat, and the risk of color shifts due to increasing temperatures. In this way, reflective color LCDs turn sunlight into a solution rather than a problem, making them an excellent option for outdoor applications.

To learn more about how Sun Vision Display can help you take your commercial signage to the next level, contact us today.