Can you look at two objects and determine whether they’re the same color? It might sound like a ridiculous question — of course you can tell the difference between colors!
Eyeballing the similarities and differences between colors might be perfectly fine in day-to-day life. But humans can only differentiate shades up to a certain point. What if you need to make sure two different objects or graphics are exactly the same color?
Fortunately, there’s an entire field — colorimetry — dedicated to just that. Let’s examine how color is measured and why we sometimes need to measure it so precisely.
Why Do We Need to Measure Color?
You might think that using online color-calibration software (or even the calibration tools that are probably built into your operating system) is an easy way to get a precise color calibration. And if you’re creating illustrations that you’ll only look at on your own screen, you might be right.
But in the vast majority of cases, digital designs are meant to be viewed on countless other screens. For example, if you’re creating a colorful ad, you want to be confident that those colors will look the same on tablets, phones, laptops, monitors, and TV screens all over the world.
If there were no way to standardize colors across screens, each of us might see something wildly different when viewing the same digital image. Modern colorimeters have the near-magical ability to account for the way we perceive color, so calibration across monitors is often incredibly accurate.
But how exactly does this measurement happen? Let’s take a closer look.
How a Colorimeter Measures Color
Measuring color on your monitor is easy — you just need to place a colorimeter directly on the monitor and let it work. Colorimeters like the one pictured above might look like simple little gadgets, but they do some seriously impressive analysis.
A colorimeter analyzes “patches” of color, and it can assign a unique identifier to every possible shade. It does this by using a color matching function known as CIE 1931 2° Standard Observer (a fundamental component of the CIE 1931 XYZ color space). As the name suggests, it was created in 1931 by the CIE (International Commission on Illumination — the abbreviation comes from its French title, Commission Internationale de l´Eclairage).
This system is incredibly complex and nuanced, but we’ll capture the essence of it here. The CIE 1931 RGB (from which the CIE XYZ color space was derived) color matching functions, generally abbreviated as “CMFs,” are based on just three “imaginary” colored lights: one red, one green, and one blue. These lights are super-saturated — so much so that every single color a human could see can be made of some combination of the three.
The system takes into account both chromaticity (the color’s coordinates in space) and luminance (the color’s perceived brightness). So when the colorimeter delivers a value for each color on the screen, it’s essentially giving an objective label to the way you perceive the color.
Each color’s value includes three coordinates: X, Y, and Z. It might seem like these coordinates would correspond to red, green, and blue. But in reality, X mostly accounts for the red and green components of a color, Y signifies luminance, and Z approximately captures the blue/yellow components.
How Results Are Plotted
So how would you visualize the reading you get off a colorimeter? In theory, you could plot each value in a three-dimensional, XYZ color space. However, most of the time, these colors are shown on something called a chromaticity diagram. Here’s an example of one:
The CIE 1931 XY chromaticity diagram is based on the XYZ color space, but they take that space and essentially flatten it. This “flattened” space just gives you information about the relative amounts of red, green, and blue in a given color — it ignores the luminance of each color completely.
These diagrams are somewhat similar to map projections. Plotting a color’s location in a 3D XYZ color space is like pointing to a country’s location on a globe. The globe gives you an accurate, three-dimensional representation of Earth.
However, using a globe is not always practical. If you need a two-dimensional representation of the world, you’d use a world map:
Much like a chromaticity diagram, a map projection (a 2D representation of a spherical globe) takes a 3D space and “flattens” it. It may not depict the 3D space 100% accurately, but it comes pretty close and offers you a convenient visualization.
Color Matching Functions Came From Wright-Guild Data
As you can see, there’s no shortage of complex mathematics going on each time you use a colorimeter. But before those formulas were even created, someone had to generate the original color matching data.
The CIE didn’t have to look too far back to find that data. In the 1920s, color scientists W.D. Wright and John Guild conducted separate but similar experiments on human color perception. In each one, study participants adjusted the levels of three primary lights until they matched a specific color.
For example, let’s say a study participant is shown an orange-colored light. He has access to a red light, a green light, and a blue light, and he must adjust the intensity of each one until the mixture of the three creates the same orange color. Both Wright and Guild asked their study participants to repeat this process for shades all along the color spectrum.
The results of the two scientists’ studies were remarkably similar, and they formed the basis for the CIE 1931 color spaces and the initial color matching functions.
Tools of the Trade: The Differences Between Colorimeters and Spectrophotometers
When it comes to measuring color, the colorimeter is a pretty common tool. But there’s a related tool called a spectrophotometer that’s also used in the field (but often for slightly different applications). Here’s an overview of the main differences between them.
We mentioned above that colorimeters analyze patches of color on computer monitors and various types of samples, but we didn’t get into what actually happens as the colorimeter measures the colors.
When you put a colorimeter on the surface of your computer monitor or a sample, it shines white light (from its own internal light source) onto the surface. That light reflects off the surface and back toward the colorimeter.
As the light reflects back toward the colorimeter, it passes through three different filters: a red, a green, and a blue. Because these types of colorimeters use three different filters to determine the RGB values, they are sometimes called “tristimulus” colorimeters.
The three filters roughly correspond to the three types of color-detecting cone cells we have in our eyes. As a result, tristimulus colorimeters can “see” color similarly to the way the human eye perceives it.
Colorimeters are advanced tools, especially considering their relatively compact size. But they do have one key limitation — because they don’t test how colors look under different kinds of light, they can’t identify metamerism.
Metamerism is a phenomenon when two colors look identical under some lighting conditions but different under others. For example, colors A and B might look exactly alike in the sunlight but completely different under a lamp:
The ability to identify metamerism is important in many applications. For example, consider interior paint. If a paint company is trying to mix a paint color that matches an existing shade, a colorimeter might verify that the colors are identical.
However, that only means the colors look the same under the kind of lighting the colorimeter uses. It’s very possible that if you put the two colors together under a fluorescent light or the light of the sun, they would look entirely different.
Many applications — like paint matching and various types of production — require a tool that can identify metamerism. Fortunately, the spectrophotometer is just the right tool for the job.
Spectrophotometers work a lot like colorimeters — they shine light onto a sample and then measure the color of the reflected light (the photo above shows one in action). The main difference between the two comes down to their filters.
Colorimeters typically have three filters or channels (red, green, and blue). However, spectrophotometers can have hundreds because they are designed to be even more precise.
There are different types of spectrophotometers for measuring different kinds of surfaces (and different kinds of paint or color finishes). Here are a few of the main types:
- 0:45/45:0: This kind of spectrophotometer measures the color of a flat, usually matte surface by beaming light down at a 45-degree angle.
- Sphere: This type measures light as it reflects off a surface from every angle. As a result, it’s often used for measuring the color of textured and/or glossy surfaces.
- Multi-Angle: If you’re looking closely at the color of an object, you might twist it back and forth under the light. By shining light on an object from several different angles, this spectrophotometer effectively does the same thing. Multi-angle spectrophotometers are often used to measure the color of complex, specialty colors like the glimmering, metallic finishes on cars.
Because spectrophotometers can look at a color sample under different lighting conditions, they can easily identify metamerism. You can find these fascinating machines in all kinds of configurations, from handheld devices to massive benchtop setups.
Colorimetry in the Real World: When Do We Need to Measure Color?
Colorimetry is a dazzlingly precise science. It’s interesting to learn about in its own right, but it also has more applications than you may think. Here are a handful of ways colorimetry touches our everyday lives.
Color Matching Paint
Say you buy a home with walls painted in a color you absolutely love. You want more of this particular paint, but there’s just one problem — you have no idea where it came from or what precise color it is!
Lots of hardware stores and paint companies offer paint-matching services and use spectrophotometers to measure the color brought in by a customer. These precise instruments can deliver a specific readout that lets the paint company mix a perfect color match.
Calibrating Monitors (and Finding Inspiration) for Digital Design
You don’t have to use a massive, super-expensive colorimeter to calibrate your monitor. Most designers recommend taking the time to calibrate your monitor about every month. Monitors degrade over time, and as yours ages, the colors might start to look different to you.
That might not ordinarily be a big deal, but if you’re designing something that will appear on many other screens, you want to make sure you see it exactly as your audience does.
Fortunately, you don’t need in-depth colorimetry knowledge to calibrate your monitor. You just need to place a colorimeter on your screen and let it “talk” to calibration software installed on your computer.
If you work in design, you also might know that portable colorimeters are great for capturing inspiration. Just as a writer might jot down ideas in a notebook, a designer can capture colors while on the go.
You might wonder why you wouldn’t just snap a photo of that inspirational color. But modern cameras don’t always record color the way we see it. If you spot a color you like, you can capture it with a portable colorimeter. The machine analyzes the amount of red, green, and blue light reflected. With that input, it can give you an exact value for the color. You can save that value and then replicate it the next time you sit down to work!
Standardizing Color Across a Brand
Color is closely associated with the brands we know and love. For instance, when we see a Coca-Cola logo (whether it’s on the label of a bottle, an online ad, or even on a t-shirt), it’s always the exact same shades of red and white.
But how do companies like Coca-Cola keep colors consistent in print and online? Most of the time, they rely on color matching systems like the one we talked about above. Using advanced colorimetry, these systems analyze various forms of color and help companies ensure that consumers are seeing the exact same palette across every format.
Colorimetry is a key part of manufacturing for obvious reasons. In many industries, the same product is made in many different locations. If there’s an issue at one plant, products from that plant might come out looking different than they should.
For example, let’s say you order a burgundy shirt online from a major company. The shirt is produced at several different locations, so to make sure each one is the exact same color, the company has a “target color” with specific XYZ coordinates.
Each location can then measure the colors of the actual shirts that come off their production line and compare them to the target color. If a location doesn’t do this, the shirts it produces might gradually drift away from the standard color — so the burgundy shirt you order might come out looking more maroon!
Some industries have developed ways to continually monitor color accuracy. For example, when producing food packaging, many companies print a series of small colored circles somewhere on the package. These circles are usually cyan, magenta, yellow, and black — cornerstones of the CMYK color model. They often look something like the column of circles to the left of this graphic:
These inconspicuous circles are called “printer’s color blocks” or “process control patches.” During the manufacturing process, major corporations typically have high-end spectrophotometers continually monitoring these blocks.
If there’s an issue with the quality or saturation of a shade, the equipment can often make instant, automatic adjustments. That way, the colors are exactly as they should be, and there’s little to no interruption of the printing process.
Seeing Our World Through a New Lens
Whether you work with color every day or are just curious about color science, colorimetry offers a fascinating way to better understand the world around us. And even if you simply admire color (and don’t work with it at all), colorimetry touches your life on a daily basis — from the clothes you wear and the cereal you buy to the color you paint your home.