In March 1975, Bryce E. Bayer — a scientist at Eastman Kodak's research labs in Rochester, New York — filed US Patent 3,971,065, titled "Color Imaging Array." It granted in July 1976 and expired in 1994. Almost every color image ever captured by a digital sensor since — from your phone camera to the Perseverance rover on Mars — is built from Bayer's four-square idea.

The problem Bayer solved was mundane and enormous. Image sensors (then CCDs, now mostly CMOS) count photons but are colorblind: each photosite records only brightness. To capture color, you could split incoming light three ways with a prism and use three sensors — expensive, bulky, needing perfect optical alignment — or you could put a tiny colored filter over each pixel, one color per site, and reconstruct the missing information with math.

Bayer's insight was which filters to use and how to lay them out. He specified a repeating 2×2 tile:

R  G
G  B

Half the pixels are green, a quarter are red, a quarter are blue. That imbalance is the clever part. The human retina has far more green-sensitive M-cones and L-cones than blue-sensitive S-cones, and our luminance perception is dominated by the green channel. Bayer effectively said: make the sensor mimic the eye. Give the color channel we're most sensitive to twice the sampling rate, and let a "demosaicing" algorithm interpolate the missing values at each site by looking at neighbors.

The patent itself is elegantly general. Bayer described a "luminance-chrominance" split: one set of filter elements sensitive to a broad band representing brightness (which he called the "luminance" set, typically green), and a second set representing color differences (red and blue). He also described alternative tilings — RGBW patterns using unfiltered "white" pixels for low light, and CMY subtractive variants — decades before any of these became commercial features. Sony's clear-pixel sensors and modern computational photography still borrow from those alternatives.

What makes the patent surprising is the era. In 1975, Kodak had just built the first digital camera prototype in-house (Steven Sasson's 100-line CCD experiment). There was no consumer digital photography. Sensors were laboratory curiosities. Bayer filed a patent for a color scheme whose entire industry did not yet exist. He was designing for hardware that wouldn't ship for fifteen years.

The modern relevance is nearly total:

• Every smartphone, DSLR, mirrorless camera, GoPro, dashcam, and security camera uses a Bayer filter (or a close variant like X-Trans or Quad Bayer).
• The demosaicing algorithms that turn Bayer raw data into RGB pixels are a whole subfield of image processing — bilinear, gradient-corrected, and now deep-learning demosaicers all inherit the RGGB assumption.
• Computer vision pipelines and machine-learning training sets almost universally start life as Bayer arrays. Your face-unlock model was trained on images shaped by Bayer's 1975 layout.
• Space telescopes and rovers use Bayer filters or their derivatives. When you see a color photo from Mars, you're seeing Bayer demosaicing applied to a sensor 200 million kilometers away.
• Modern "quad-Bayer" sensors group four same-color pixels for high-dynamic-range and pixel binning on phone cameras — a direct descendant of the 1975 tile.

Bayer himself was quiet about the achievement. He worked on halftone printing and image compression for the rest of his career, retired in 1986, and died in 2012. His obituary in The Rochester Democrat and Chronicle was a short paragraph. There is no monument, no Nobel, no museum exhibit. Just a two-by-two grid of colored squares, repeating trillions of times per second across every camera on Earth.