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Advanced Imaging Magazine

Updated: January 12th, 2011 09:49 AM CDT

Image Analysis in Black & White

Monochrome often can provide a greater range of digital information than color images
Figure 1: The complete visible spectrum: The dotted line shows the human eye’s sensitivity for night vision. Sensitivity is the largest in the blue-green portion of the optical spectrum. (Wiki: Bob Mellish)
Figure 2: Incoming light on Bayer-filtered photodiodes (below) (Wiki: Colin M..L. Burnett)
Figures 3, 4, 5: A composite (top) of red, green and blue filters (bottom of facing page); a combined channel image (above) created from the three separate and complete color channels above it.
Figure 6: A separation prism. (wiki: Colin M.L. Burnett)
Figure 7: Artifacts visible with a standard color CCD camera (top) and no artifacts with a 3CCD color camera or a b&W camera.
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By Francois Marceau
Clemex Technologies

Conventional wisdom holds that digital color images are superior to digital black and white images for Image Analysis (IA) due to the fact that they are true to life, to reality as we perceive it. Even when analyzing monochrome images, digital color images transformed into grayscale are considered superior. The following article will attempt to dispel this assumption by showing that monochrome digital images offer a greater range of information than color images due to the filtering techniques used to acquire color images through digital formats.

Throughout most of history the human eye was the only type of detector available to us. Versatile and sensitive, the human eye can detect the visible spectrum but has its limitations, low-light vision being one of them. In fact, the human eye only can detect a small portion of light spectrum; from violet, with a wavelength of 450 nm, to red, with a wavelength of 750 nm. For the human eye, distinguishing colors is based on the sensitivity of the retina’s cells to specific wavelengths within light’s spectrum. The same can be said about cameras.

In 1826, Joseph Nicéphore Niépce, using a sliding wooden box camera made by Charles and Vincent Chevalier in Paris, created the first permanent photograph. Using a silver and chalk mixture that darkened in contact with light, the first black & white picture became a reality. During the 19th and early 20th centuries the process for obtaining black & white images grew, cutting exposure time and dramatically simplifying the medium on which the image was exposed. In 1935 the Eastman Kodak Company introduced the first modern color film, Kodachrome, using three colored emulsions: red, green, and blue. Color photography came to the masses in 1963 with the introduction of instant color film, developed by Polaroid. But the real revolution was yet to come.

In 1969 Willard Boyle and George E. Smith of AT&T Bell Labs designed what they termed a “Charge Bubble Device,” later renamed Charge Coupled Device, which was in fact a kind of memory device. However, they determined that the CCD could receive charges via the photoelectric effect, which in turn could create electronic images; thus the CCD digital camera was born. And, as with the first photographic cameras, digital cameras originally produced black & white images.

A CCD is a collection of individual pixels (photodiodes) defined in a silicon matrix by an orthogonal grid. It transforms photons, which it receives in electron/positron pairs, by photoelectric effect in the semiconductor substrata, absorbing much of their energy, resulting in the liberation of the electrons, and the formation of corresponding electron-deficient sites.

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