Celebrating the brilliance of Bryce Bayer and his exceptional Bayer Sensor innovation
The Bayer color filter array, a design concept introduced by American scientist Bryce Bayer of Kodak in 1974, has been a foundational element in color image sensing since the 1970s. This ingenious design arranges red, green, and blue filters in a 2x2 microscopic mosaic pattern over the photosites of an image sensor.
The Bayer array cleverly balances color accuracy, spatial resolution, and light-use efficiency. It achieves this by favouring green filters, which mimics the human eye's greater sensitivity to green light. This design ensures good image quality with manageable hardware complexity.
The array consists of two luminance elements for each chrominance one, favouring the parts of the spectrum to which the eye is most responsive. The other two curves in the Bayer sensor have significant response in the luminosity region. This optimisation of the sensor's spectral sensitivity and spatial sampling maximises luminance data, which is critical for sharpness and detail, while still capturing red and blue color information for accurate color reproduction.
However, traditional Bayer filters do block a significant portion of light, roughly 70%, because the filters selectively absorb non-matching wavelengths. This limitation has led to modern advances seeking to improve upon the Bayer design. Technologies like vertical waveguides, which split light without filtering it away, can triple sensitivity and reduce light loss.
In Bayer's original patent, the filters are described as 'luminance' (green) and 'chrominance' (red and blue) elements. The luminance (green) filters in a typical Bayer filtered sensor are closely tailored to the human luminosity response curve. The solar radiation spectrum closely matches the peak of the human visual responsivity, further emphasising the Bayer array's optimisation of the sensor's performance given the Earth's environment.
Despite multiple attempts to produce 'full color' sensors, the Bayer sensor still rules supreme. The company that dominates the market for the films used to make Bayer Colour Filter Arrays is Kodak's great rival, Fujifilm.
Figure 1 shows the Bayer color filter array, and Figure 2 shows the spectral response curves for the color filters compared to human luminous sensitivity. The grey curve in Figure 2 shows the shape of the spectrum of human luminous sensitivity, while the red, green, and blue curves show the response of the color filters.
Unwanted color shifts occur in cameras without blocking filters when results of extending sensors into infra-red and ultra-violet parts of the spectrum are taken to their logical conclusion. However, the Bayer design does not extend sensors into these regions to increase sensor efficiency in areas where the eye is less responsive.
Professor Newman discusses the Bayer color filter array as a clever design for image sensors, enhancing luminance detail and overall perceived image quality with relatively simple hardware. This design efficiently uses the sensor area to gather light across the visible spectrum while avoiding the complexity and light loss of alternatives, such as full three-sensor systems or more complex multispectral filters.
Data-and-cloud-computing technologies have enabled advanced image processing and analysis, optimizing the performance of Bayer color filter arrays. The technology assists in overcoming the traditional limitations of the Bayer design, such as light loss, by developing new approaches like vertical waveguides.
The optimization of the Bayer sensor's spectral sensitivity and spatial sampling is a testament to the role of technology in data-and-cloud-computing, allowing for multi-spectral imaging and enhancing image quality.
