There are billions of monitors worldwide that can reproduce the same color when instructed to, which is an engineering achievement. However, this is only achievable with a standard definition for colors. Previously, colors were defined using a limited set of words, with most languages having at most twelve words to describe colors. While these definitions suffice in many situations, they lack the precision needed to describe subtle differences between similar colors, which is essential for accurate color reproduction.
The colored rectangles illustrate various shades that can all be labeled as green. They could also be described with terms like lime-green, olive-green, light-green, and dark-green, but this naming system is inefficient. A more effective approach would be to use numbered units to describe colors, allowing for precise representation by adjusting the number of digits used. This concept of mapping colors to numbers, while unconventional, aligns with the quantification of other measurable physical phenomena, such as distances and temperatures.
Defining colors numerically raises intriguing questions, such as how color addition or multiplication would manifest. It also highlights the limitations of color hex codes, which cannot represent enough colors despite having 16,777,216 values, and touches on cultural phenomena like the viral debate over a dress's color and the existence of color blindness.
The aim is to measure colors as physical entities. Although colors are subjective, the general agreement on color perception suggests an underlying objective and physical nature. Colors are visible only in the presence of light, which is a key aspect of their definition. Light can be conceptualized as wave-like particles called photons, each carrying a specific amount of energy determined by their wavelength or frequency.
The electromagnetic spectrum encompasses photons with varying energies, ordered by wavelength or frequency. The energy of photons can be measured, allowing for the quantification of light. For comparative purposes, energy measurements are normalized per unit time as power and per unit area as intensity, with intensity measured separately for different wavelengths, resulting in a spectral power distribution.
The spectral power distribution quantifies light, but a quantitative relationship between colors and this distribution is necessary. Color perception relies on light and the human eye, which reacts differently to various wavelengths. Human eyes contain photoreceptor cells that respond to specific wavelengths, closely aligned with those emitted by the sun (380nm–750nm).
Photons can excite photoreceptor cells, producing specific responses. The human eye has two types of photoreceptor cells: rod cells and three types of cone cells, each sensitive to different wavelengths. The varying sensitivity of these cells allows for the distinction between different wavelengths of light. For instance, a monochromatic light source will elicit different responses from the cones based on their sensitivity to that wavelength.
The unique responses generated by different wavelengths enable the brain to perceive distinct colors. While wavelengths that are close together may produce similar responses, distinct wavelengths yield unique sets of responses, allowing for differentiation in color perception. Rods, which are more sensitive to light than cones, do not significantly influence color perception in well-lit conditions, as their response saturates and does not provide meaningful information about wavelength.
In summary, while the quantification of color presents challenges, understanding the relationship between light, color perception, and human physiology is crucial for developing a more precise system for defining and reproducing colors.