Color Theory Fundamentals for Digital Photography

Adapted from The Essential Color Manual for Photographers (Rotovision)

By Chris Rutter


It is easy to take color for granted; after all, it is how we see the world every day. But color plays such an integral part in our emotions and in our perception of a scene that knowledge of the nature of color and how to capture it in your images will give impact and expression to your photography.


The difference between these two images is simple: one is mainly orange and one mainly blue. However, the difference in the overall feel of the two is marked. The orange image is welcoming and warm. In the blue image, the whole scene looks cold and uninviting. Why these colors cause such differing emotions is largely psychological. The ability to measure the color differences and manipulate them allows us to capture more than a simple representation of a scene; it allows us to create a more personal view of the world.

Painters and designers learn how color can be used to their advantage at a very early stage, but for most photographers learning about this issue is often a question of trial and error. Traditionally, this has been because photography did not offer the same artistic license as other visual media. Simply capturing the world around them meant that there seemed little point in photographers learning how to mix colors and use color contrasts. However, digital photography has opened up a whole new world of creative possibilities, by offering everyone the opportunity to create their own vision of the world around them, including the ability to adjust or even to change colors.

Traditionalists may not hold with this level of manipulation, but does anyone object to black-and-white photography? That is surely the greatest manipulation of all, and it has been at the heart of photography since its very beginning. Even capturing images on color film is not a pure recording medium. Film does not “see” light in the same way as we do; as soon as you press the shutter you are manipulating reality, so make the most of it and use color to your advantage.


It is easy for us to identify the colors of this image as wrong, but what has caused the color cast and how do you eliminate it? Without some knowledge of how colors appear and basic color theory, it would take far more trial and error to find a solution than is necessary. This is why it is important for photographers to learn something about how colors work before embarking on the more creative aspects of color photography.

Knowing how to use color effectively will expand your creativity and your awareness of why some images work while others fall flat. It is also valuable to know about the more technical aspects of the subject: color accuracy and knowledge of light sources will make it easier for you to capture the image accurately in camera. This mixture of artistic and technical aspects lies at the heart of photography. Concentrating solely on the technical factors of your images—the exposure, sharpness, and so on—can result in dull and contrived images. But without some technical knowledge, you will struggle to get the most from your photography. This is especially true of color and how you use it effectively in your images. If you concentrate solely on getting the color technically correct, you will miss out on a whole world of images.

You need to be able to spot the potential of the colors in a scene and then use them in your images. This process starts long before you even pick up the camera; it involves how you see colors and how they influence our perception of the world. Honing these skills, along with the ability to capture them to recreate the impact they had on you at the time, is the key to producing great color photographs.

Even when you don’t have your camera with you, keep your eye in by looking at the scenes around you. You  will soon see how many of the things we take for granted use the same color principles that you can use in your photography. This includes how nature uses color to attract or deter other creatures, and how designers and architects use color to create an emotional reaction when we use their products or  buildings.

Be aware that, for all our knowledge and technology, there are still aspects of color and light that we do not fully understand. Even the way that we actually see colors is a mystery; although the basic physical aspects are known, how our brains interpret the information gathered by our eyes is still open to much speculation. For me, that is what makes color photography such an interesting medium. Color has the power to create moods, evoke emotions, or show the world in ways that would otherwise be invisible or lost to our everyday lives. By carefully selecting, adjusting, or manipulating the colors present in an image, it can be given a meaning that can be as blatant or as subtle as you like. Before we get started on the photographic aspects of color, we need to find out what color is and why we react to colors differently. In this article we will investigate the basics of color theory, along with the science behind our vision, and how we have tried to quantify and categorize colors. It is, of course, possible to explore the creative use of color without this groundwork. But with more and more photographers taking control of the whole imagemaking process, from capture through to printing, the need for an understanding of how and why colors appear as they do is becoming more important. So let’s see why colors look the way they do.

What Is Color?

As long ago as the 6th-century in China, people have tried to understand how and why we react to different colors and how the various colors work together. This ongoing study has produced many theories about the nature of color, all with a similar theme at their heart.

Color theory is based around the existence of three colors that, when mixed together, can produce all other colors. These colors, known as the primary colors, vary according to their application. As photographers, we are mainly concerned with the properties of light, so that is what we will concentrate on here.

Additive Color
The three primary colors of light are red, green, and blue (RGB). Combinations of these building blocks can be used to produce all of the colors in the visible spectrum, and equal amounts of all three produce white light. Because these colors are added together to make white, they are known as additive primaries. Mixing equal amounts of two primary colors together produces what are known as the secondary colors. These are: yellow (red + green); cyan (green + blue); and magenta (blue + red). The easiest way to visualize these relationships is using a diagram known as a color wheel.

By placing the different colors around a circle you can see how the colors work, and how they influence each other. The primary colors are equally placed around the wheel, with the secondary colors placed between the two colors that, when combined, make that color.

The colors that are next to each other on the color wheel are known as harmonious or analogous colors. This is because when you see them together they give a sense of calm and peace, or harmony. Colors opposite each other on the color wheel create the maximum contrast and are known as complementary colors. When viewed together, these colors can clash, creating a striking image. These two relationships between colors lie at the heart of color theory. Color theory has been used by both scientists and artists for centuries, allowing them to categorize colors, or exploit them for visual effect.

Subtractive Color
Unfortunately, the red, green, and blue additive primaries do not apply to every situation. To explain how printing inks produce different colors, you have to consider a different set of primary colors: cyan, magenta, and yellow (CMY). When combined in equal amounts, these three colors produce black, and are known as subtractive primaries (in printing, these colors are known as CMYK; the “K” stands for black to avoid confusion with blue, although originally “K” stood for “key plate”). If you look at the color wheel diagram, you will see that this is simply a reversal of the primary and secondary colors.

Because cyan and magenta are not often encountered in their pure form in nature, subtractive color is best considered as a technical aspect of printing, rather than as a color theory for explaining color combinations. We will investigate it further when we discuss the process of color printing.

Another set of subtractive primary colors is yellow, red, and blue (YRB). This system is based on pigments and is therefore of most importance to painters. These three colors are those that aren’t created by mixing any other colors, so are the primary colors. This produces a color wheel that varies slightly to the RGB model. But the colors are essentially in the same order around the wheel. So, despite the differences, you can apply both in a similar way.

Summary of the Uses of Primary Colors
With three different combinations of primary colors, it can be confusing as to which should be used. Here are the technical uses for each.

Additive
• Red, green, and blue (RGB): light, digital cameras, and displays

Subtractive
• Cyan, magenta, and yellow (CMY): commercial printing and some home printers
• Yellow, red, and blue (YRB): painting and art theory

Which Color Theory is Best to Use?
As photography is concerned with the action of light, it is easiest to concentrate on using RGB as the primary colors. While there are differences between the relationships of the color in this and the YRB primaries, they both use colors in the same basic order on their respective color wheels. So neither is necessarily best to use, just more convenient.

Despite being the same color saturation and intensity, the yellow swatch appears much brighter than the blue next to it. This discrepancy in our color vision plays a large part in how we react to certain colors in an image.

Color Intensity
While the basic theory of primary and secondary colors is useful as a starting point, it does not fully explain how the colors work together. In this model, all the colors are presumed to be perceived equally. Unfortunately, our vision is not a precise instrument and we see colors differently, even though they have equal intensity.

For example, we generally perceive blue and green tones as being much darker than reds or yellows of the same intensity. This perception is partly physical, but is also due to the world around us. In nature, most blue and green objects, such as a clear sky or foliage, are non-threatening, so we don’t need to pay so much attention to them. Red and yellow are more often encountered with objects that we need to pay attention to—blood or dangerous animals, for example—so we are accustomed to perceiving these colors as brighter and more eye-catching. These reactions mean that if we see an image with equal amounts of two primary colors—for example, red and blue—the red appears much stronger and more prominent.

Light

Much of our knowledge about light derives from experiments that the scientist Sir Isaac Newton (1643–1727) carried out in the 17th century. He demonstrated that daylight can be split into a series of colors. This sequence of colors—red, orange, yellow, green, blue, indigo, and violet—is known as the chromatic color sequence. Colors that are not part of this sequence, such as beige or burgundy, are known as nonchromatic colors.

The nature of light itself is still the subject of much speculation. Current theories explain light by giving it the properties of both waves and particles. We will deal primarily with the wave theory; this explains the aspects of light, such as wavelength and frequency, that concern us in color photography.

Light Waves

The easiest way to understand light waves is to imagine holding a string that is fixed in position at the other end. By vibrating this string, you create waves traveling along it. The faster you vibrate it, the narrower the distance between the crest of each wave. The slower you vibrate it, the longer this distance. This spacing between the points is known as the wavelength.

It is this difference that creates the different colors within the spectrum. The brightness of the light is due to the amount of energy produced by the light source. While this has an influence on photography, it does not directly affect the colors produced.

Light waves are the visible part of a much larger group of waves known as the electromagnetic spectrum, which includes X-rays and radio waves. The  range that is present in daylight is shown below. This ranges from the short-wavelength ultraviolet to the longer-wavelength infrared, with the visible portion in between.

While our eyes cannot see ultraviolet or infrared radiation, these can have an effect on the image produced by both digital sensors and film. In most circumstances, it is undesirable for the image to register radiation outside of the visible spectrum. However, it is useful for both scientific and artistic applications for producing images of a world beyond our visible experience.

Why Objects Appear  Colored

When we see an object lit by white light, its color is due to the object absorbing some colors and reflecting (or transmitting) others. For example, green foliage appears to be green because it contains pigments that absorb blue and red light and reflect only green light. It is a similar story when the light is viewed through an object, such as a photographic filter. You only see the part of the spectrum that is allowed through. For example, a blue filter blocks red and green light, and allows only the blue part of the spectrum through.

Measuring Colors

Human vision is very good at recognizing the differences between two colors seen side by side. However, it is a different story when it comes to accurately describing individual colors to someone else. Accurate color classification is an important aspect in color-management systems, which we discuss in detail later.

As an example, look at the colors of the flowers and background in the image below and try to accurately describe the two colors. Without being able to relate each to another color, you will struggle. You can say that the flowers are purple, or magenta, but it is almost impossible to relate that to someone who hasn’t seen the color, even if they have a selection of colors to choose from.

There is also the matter of personal interpretation of different hues; as we will see in the section on how we see color, each individual has their own idea of what colors should look like. So, even if you have “perfect” vision, you cannot quantify the colors that you see without comparing one to another, and even this is open to massive differences in our interpretation of the color.

Describing Colors

Even though we can see colors accurately, it is very difficult to describe them without a reference point to relate them to. That is what color measurement is designed to do.
To accurately describe colors for color matching, especially when we delve into the world of digital imaging and color management, we need a more reliable method. In order to describe a specific color, we need to break it down into three elements:
  • Hue: the name given to the color itself. This is defined by the name given to the main wavelength contained within the color, such as blue, green, magenta, and so on.
  • Saturation (or chroma): the purity of the color. In many instances, especially in print or pigments, mixing black, gray, or white to a color will result in lower saturation.
  • Luminance: the brightness of the color. In pigments or print, this describes how much incident light the color reflects; in the case of a light source, it describes how much light is emitted.

By using these three measurements, any color can be described so that it can then be recreated accurately throughout an imaging system. An understanding of these measurements will help you to understand the relationships between the colors in the scene that you are photographing and how these will be reproduced in the final image.

There are two main systems used to define colors and give them a specific numerical value: the Munsell system, and the CIE (Commission Internationale d’Eclairage) system.

The Munsell System
Originally developed by American artist A. H. Munsell (1858–1918), this system, shown at right, was designed to classify standards for printing inks, color pigments, and artists’ paints. It uses a collection of color charts made up of printed color swatches for each hue. Each color is assigned a number to define the hue (the chart that it appears on). Further values for luminance and saturation give vertical and horizontal coordinates to indicate where it appears on this chart. Therefore, as long as you have these three values, you can find the color on the Munsell chart and use it to ensure that it remains constant throughout an imaging system.

Because it is based on the pigments and inks available for printing, the Munsell system has only a limited use for photography. It cannot define many of the colors that you will come across in many situations—for example, the colors produced by a light source, or substances that have no direct pigment equivalent, such as fluorescent, or the phosphers used to produce the image on a computer screen.

However, the Munsell system is still in common use in the printing industry and some areas of graphic design; if you are producing images for magazines, you may come across this system for defining the colors that they are able to produce.

The CIE System
The CIE system is much more suited to classifying color in photography. It is usually shown in the form of a chromaticity diagram (see diagram). It classifies colors by equating them to the quantity of red, green, and blue light that need to be mixed together to produce a color. This is shown graphically so that every color that it is possible to define can be placed by defining its X and Y values.Because it is based on the mixture of red, green, and blue light that forms the basis for most digital imaging, this system has become the standard for digital photography. This makes it the most suitable system for defining the colors in color-management systems.

Why Do We Need Color-classification Systems?
When we photograph a scene, we will come across a huge range of colors and tones. Color-classification systems mean that it is possible to predict how these colors will be reproduced by each device that you use to produce the final image.

The Gretag Macbeth ColorChecker is the most commonly used standard for producing accurate results.
As a photographer, knowing how your camera, computer monitor, and printer will cope with the colors it encounters will help you produce the image that you visualized at the time. Knowing, for example, that your printer will struggle to reproduce the greens in the original scene means that you can try to adjust how you shoot the scene in the first place so you won’t be disappointed in the final image.

Viewing
Because the color that we see is affected by the color of the light falling on it, any color classification based on color swatches relies on a standard light source for viewing. To  accurately assess any color in a print, you need to view it under the right lighting. The  most common type of light is known as standard daylight, and specialized viewing booths used in commercial printing use lights designed to produce a very accurate color. These booths are beyond the means of most photographers, but you can buy daylight bulbs relatively cheaply that are accurate enough for all but the most critical uses. Try to set aside an area of your workspace that doesn’t contain any strong colors for you to accurately assess the colors of your prints.

Your attention is immediately drawn to the red car in this image, despite the fact that it occupies only a small area of the frame. This is due to many factors, one of which is the fact that red is associated with danger. Consequently, we pay more attention to red than to the colors around it.

How We See Color

Trying to understand how color is recorded photographically without knowing how we see color is like trying to cook a meal without ever tasting food. While photographic materials record colors in a predictable and measurable way, it is how we see and react to both the original scene and the final results that makes or breaks the process.

While you may think that you see colors with your eyes, it is actually the brain’s interpretation of the information that determines what we see. This can be influenced by personal and cultural factors (certain colors have specific meanings in different countries, for example). Despite these variable factors, there are also many deep-rooted reactions that seem to be almost universal, and these can be exploited in your photography.

Physical Aspects of  Vision
Let’s discuss some basic physical aspects of vision before describing how we use this information. As we have seen, light is made up from three primary colors—red, green, and blue—and this is basically how our eyes see color. The light-sensitive cells within the eye are split into two main types: rod-shaped and cone-shaped. The rods are the most sensitive to light, but cannot discriminate between different colors. The cones are less sensitive to light, but contain chemicals that allow them to see one of the three primary colors. The blue- and green-sensitive rods equate very well to the colors that we think of as pure primary colors, but the rods that we use to see red light are only sensitive to light that we would consider to be orange. The information given by these three types of rod is sent to our brain, which interprets the information to give us a mental picture of the scene. So, while our eyes play a major part in the physical aspects of vision, it is our brain that determines what we see.

Color blindness test chart.
Limitations of Color Vision
There are many factors that mean that the colors seen by one person may not match those seen by another. Here are the most common problems to bear in mind when trying to assess color correctly.

Color blindness: As opposed to the psychological influences that mean we all interpret colors differently, color blindness is a physical aspect of the reaction within the eye. This can take the form of a slightly uneven response to the three primary colors, or can result in an inability to distinguish between red and green. Color blindness affects around one tenth of the male population, but is much less common in females. At its most severe, color blindness can cause problems with achieving accurate color balance, so it is worth checking out whether you suffer from this condition by using some of the charts readily available, or asking your optician.

Color memory: The human mind can be lazy at times; rather than making the effort of analyzing what we see, it often makes up information because it is easier to do so. If we see an object that we “know” should be a particular color, then the brain tells us that’s what we are in fact seeing. For example, when you see a picture of a blue sky, your brain doesn’t necessarily see the actual color, because you already know what color a blue sky should be. On the other hand, we take far more notice of the precise color of other objects, such as food or skin, because these are areas that, historically, we need to see precisely.

Brightness and adaptation: Like the aperture of a lens, our eyes have an iris to govern the amount of light allowed through. In dark conditions, once the iris is fully opened, the eye increases its sensitivity to allow us to still see. This  extra sensitivity is controlled by the rod-shaped cells within the eye, so we get less and less information from the color-sensitive cone-shaped cells. As the light levels drop, our sensitivity to color shifts more toward the blue-green end of the spectrum, until there is no color information at all.

This adaptation is also partly responsible for our ability to “correct” different light sources. When you move  quickly from an area lit by daylight to an indoor situation lit by incandescent light, the scene will appear much more yellow. After a short while in this lighting, your vision will adapt, making the scene appear more neutral. Neither digital nor film cameras and materials react to light this way, so have to be adjusted to give a result closer to our vision.

Color fatigue: Our perception of an individual color can be affected by the color(s) surrounding it. This is partly a psychological reaction, but it is also due to the receptors in the eye becoming fatigued and influencing what you see. For example, if you place two identically colored objects against two differently colored backgrounds, the color of the object will often appear to be different.

Despite all these limitations, our vision is still remarkably good at assessing the world around us and how it can be captured photographically. The more you learn to see the world around you, the more likely you are to be able to interpret color correctly—and translate that into your photographs.


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Excerpted with permission from The Essential Color Manual for Photographers (Rotovision) by Chris Rutter. Copyright © 2006 Rotovision.