Human Vision and Color Perception
The scientific study of sight and the behavior of light (formally known as optics) can be traced back more than four thousand years to the development of lenses by the ancient Egyptians and Mesopotamians. In the 17th century, Sir Isaac Newton demonstrated how all the colors of the spectrum are derived from or combine to create white light. In the intervening centuries, we’ve garnered a great deal of knowledge of how our physiology, the structure and components of our eyes, enable us to perceive light and create vision. This knowledge has also given us a greater understanding of how we perceive color(s).
For our purposes here and to simplify matters, we want to address several aspects of color perception due to their relevance to the printing process and, particularly, in regards to the difference between the colors we perceive in our normal vision, the colors that can be displayed on computer monitors or screens, and the colors that can be reproduced in print.
Color Spaces
Science has determined visible light comprises but a small portion of the greater electromagnetic radiation surrounding us at all times. Radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays are other aspects of electromagnetic radiation we can measure but are not visible to human sight. While we have determined and measured the full range of colors available to human vision, we currently do not have the technology to reproduce or display this full spectrum. Hence, the range of colors any given technology can display or reproduce is defined by the “space” it occupies in the full visual spectrum (see illustration above). The general rule of thumb is to recognize humans can perceive far more colors and subtleties of light than can be displayed on a computer monitor, television screen, or reproduced in print.
Additive Color & Subtractive Color
There are two primary modes or types of color perception: additive color and subtractive color. Additive colors are colors created when different wavelengths of light combine and are perceived directly by the retinas in our eyes (e.g., the colors we see on a computer monitor or television screen). Subtractive colors are the colors we perceive from light that’s been reflected off an object that has absorbed all other wavelengths of light. In other words, an apple is red because it has absorbed all other color wavelengths but reflects the red wavelength.
Why is it important to note these two different aspects of color perception? Because humans can perceive a difference in the quality or nature of a color created by additive wavelengths of light and those created by subtractive wavelengths of light. This ability to distinguish or recognize a difference in colors becomes significant when talking about what colors to expect when a printed piece goes to press. For general purposes, it can be helpful to use RGB (red, green, blue) as shorthand for additive color, and CMYK (cyan, magenta, yellow, black) as shorthand for subtractive color in the context of color printing.
Subjective Perception of Color
Science measures and quantifies electromagnetic radiation at atomic and subatomic scales with instruments of enormous sophistication. Thus, while the physical nature of light is well understood and defined, human perception of light and color is somewhat more problematic. Flesh and blood human beings are, of course, not machines and sensitivity to light and color varies from individual to individual. For instance, some people are color-blind to certain wavelengths of light. Men, in particular, are often deficient in their ability to see light in the red-green spectrum. Other people may have a greater sensitivity or reception to light and color. In recent years it has been found there are a few rare individuals that, due to a genetic mutation or anomaly, have been blessed with an extra cone cell in their retinas enabling them to see millions of more colors not visible to most humans. In addition, people may associate a given color with a specific emotional state whether positive or negative. Hence, the subjective experience of color, while not predictable, is a factor when evaluating the response to a printed piece.
In our next blog post (Part II) we’ll talk about printing in color and the processes involved.
