By the end of this lesson, students will be able to:

A color space is a three-dimensional mathematical model that defines how colors are represented, organized, and displayed in digital systems or devices. It provides a systematic way to describe colors using numerical values, allowing for consistent communication and reproduction of colors across different platforms and devices. By defining color in a standardized and universally understandable manner, color spaces ensure that colors remain consistent and accurate when displayed or reproduced across various devices and platforms.
   
In a color space, colors are typically represented as coordinates in a three-dimensional space, where each axis corresponds to a specific color component. The most common color spaces are RGB (Red, Green, Blue) and CMYK (Cyan, Magenta, Yellow, Black), which are widely used in digital imaging and printing. Different color spaces serve various purposes and are suitable for specific applications. For example, RGB is commonly used for displaying colors on electronic screens and in digital media, while CMYK is used in printing processes to create physical copies of images. There are also color spaces designed for specific industries, like Lab color space, which is used in color science and image processing applications.

The CIE Lab color space, often simply referred to as Lab color space, is a color model created by the International Commission on Illumination (CIE) in 1976. It is designed to approximate human perception of color and is widely used in color science, color management, and image processing applications.
   
The key features of the Lab color space are:
   
1. Perceptual uniformity: Unlike some other color spaces, Lab color space is designed so that the numerical distance between two points in the space corresponds to the perceived difference in color by the human visual system. In other words, a given numerical change in the Lab values represents a consistent and equal change in perceived color.
   
2. Device-independent: Lab color space is considered device-independent, meaning it is not tied to any specific device or technology. It is designed to be a standard reference color space that can be used to accurately describe colors, regardless of the display or printing device.
   
3. Wide color gamut: Lab color space encompasses a wide range of visible colors, making it suitable for a broad range of color-related applications, such as color matching, color correction, and color management in various industries.
   
Due to its perceptual uniformity and device-independence, the Lab color space is a valuable tool in color science, color reproduction, and color-related research. It is commonly used for tasks like color calibration, color matching in graphic design, and evaluating color differences in quality control processes.

Rather than exploring random points, we can explore some well-known color palettes such as the X11 and HTML by plotting these colors in various three-dimensional color spaces. Select a palette of interest from the left-hand drop-down menu below, and then toggle through a few different color spaces. Notice how each individual point is represented by a different set of coordinates on a different set of axes in each color space.

(a) What are the labels on each of the axes for the RGB and Lab color spaces? For the RGB colorspace, what property is plotted along each of these axes? What connections can you make between the construction of this color space and what you know about cones in human vision?

To explore what is plotted along each axis for the Lab color space, we may need some extra help. Let's explore a color swatch calculated as a function of the variables, L, a, and b, which are found along the axes of the Lab color space. Please note that colors are not defined for all combinations of L, a, and b values; as a starting point, try L = 75, a = 0, b = 0. Then, slide a or b in either the positive or negative direction. Note that the magnitude of the a and b axes are arbitrary.

(b) What property is plotted along the L, a, and b axes for the Lab color space?

1. Christie, R. The Physical and Chemical Basis of Colour. In Colour Chemistry. 2nd Ed. Royal Chemical Society: Cambridge. 2001. pp. 12-21.
2. Stockman, A., MacLeod, D. I., & Johnson, N. E. (1993). Spectral sensitivities of the human cones. Journal of the Optical Society of America, A, Optics, Image & Science, 10(12), 2491–2521.

Selection of Additional Readings and Resources

Baumann, U. https://www.colorsystem.com/?page_id=551 (accessed 2023-09-07).

       A webpage summarizing and visualizing the evolution of color systems and color spaces from Plato to CIELab and other modern-day models.

Buether, A.; Augsburg, A.; Venn, A. In Colour: Design principles, planning strategies, visual communication; Institut für Internationale Architektur-Dokumentation, 2014; pp 33–37.

        A chapter on color systems and color spaces and their importance in art and designer from the perspective of a designer.

Ciechanowski, B. Color Spaces – Bartosz Ciechanowski. https://ciechanow.ski/color-spaces/ (accessed 2023-09-07).

       An interactive webpage by Bartosz Ciechanowski that explores the technical aspects of how additive color (colored light) can be mapped onto the RGB colorspace for use in screens.

Coblis - Color Blindness Simulator. https://www.color-blindness.com/coblis-color-blindness-simulator/ (accessed 2023-09-07).

       An interactive webpage that simulates various types of colorblindness for those of us with standard color vision. See if you can guess which cone cell type might be affected for each type of vision.