Since the dawn of human existence, countless individuals have walked the Earth, yet only a select few have glimpsed a unique color that may have existed since time immemorial. Among those who have experienced this ‘dazzling’ hue are three researchers from a dedicated team and two colleagues from the University of Washington in Seattle.
To make this color visible, a specialized ‘technicolor technique’ was devised and implemented. The requirement for a laser, affectionately named ‘Oz,’ necessitates a discussion of the underlying biological mechanisms involved.
The human retina contains three types of cone cells, which are specialized photoreceptors attuned to various wavelengths of light. S cones are most responsive to shorter wavelengths, corresponding to blue, M cones react to medium wavelengths perceived as green, and L cones are sensitive to longer wavelengths seen as red.
The brain processes input from these three cone types and combines them, allowing us to perceive the full spectrum of colors. However, each cone type’s sensitivity overlaps with others. For instance, light that stimulates M cones might also affect S or L cones, depending on the specific wavelength involved.
Professor Ren Ng from the University of California at Berkeley, specializing in electrical engineering and computer science, provided insight to Scientific American, saying, “There’s no light in the world that can activate only the M cone cells because, if they are being activated, for sure one or both other types get activated as well.
“The name comes from the Wizard of Oz, where there’s a journey to the Emerald City, where things look the most dazzling green you’ve ever seen,” Ng told the publication.
Ng is among the five individuals who have seen the color, referred to as ‘olo,’ which he described as ‘blue-green with unprecedented saturation.’ Teal is the closest color comparison.
The abstract of the research paper states: “We introduce a principle, Oz, for displaying color imagery: directly controlling the human eye’s photoreceptor activity via cell-by-cell light delivery.
“Theoretically, novel colors are possible through bypassing the constraints set by the cone spectral sensitivities and activating M cone cells exclusively. In practice, we confirm a partial expansion of color-space toward that theoretical ideal.”
The paper further explains: “Attempting to activate M cones exclusively is shown to elicit a color beyond the natural human gamut, formally measured with color matching by human subjects. They describe the color as blue-green of unprecedented saturation.”
Additional experiments revealed that subjects could perceive Oz colors in image and video form. The prototype targets laser microdoses to thousands of spectrally classified cones under fixational eye motion, showcasing a proof-of-concept for programmable control over individual photoreceptors at a population scale.