Facsimile and static presentation processing – Natural color facsimile – Scanning
Reexamination Certificate
2002-03-18
2004-08-03
Lee, Cheukfan (Department: 2622)
Facsimile and static presentation processing
Natural color facsimile
Scanning
C358S515000, C358S506000, C358S513000, C358S509000, C356S317000
Reexamination Certificate
active
06771400
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of technical reproduction of graphical images. In particular it relates to a hyperspectral system for measuring and transforming light from individual pixel elements, or pixels, that comprise an image, into a standardized representation where each pixel's notation is a location in a perceptual color space defined by the Commission Internationale de l'Eclairage (CIE).
BACKGROUND OF THE INVENTION
Conventional apparatus for capturing colored graphical images utilize a method based upon an industrial implementation of a central color science concept, the Trichromatic Generalization, which explains how colors mix and match. In the conventional scheme, a coordinate system characterized as a Device Dependent Color Space (DDC) utilizes linear mixtures of three arbitrary primary colors to match the color of individual pixels of the original.
Color Science evolved over more than 300 years of experimentation and observation and is called colorimetry. A complete review of colorimetry or the specification of human color perception is beyond the scope of this document. However, key physiological, physical and psychological factors central to determining any calorimetric system's accuracy and precision are reviewed.
The origin of the scientific Trichromatic Generalization has its basis in human physiology. The sensation of color is a complex interaction of the human nervous system with light, electromagnetic radiation found between the wavelengths of 300 nm and 830 nm (as illustrated by FIG.
1
). Ordering the psychological designations of color perception creates the visible spectrum, from short to long wavelengths, violet, blue, green, yellow, orange, and red. The color matching rules of the Trichromatic Generalization are used to predict how mixtures of the different wavelengths are perceived by humans. Complicating the mechanical aspects of color perception are visual system anomalies.
The human eye's lens brings different wavelengths of light to focus at different distances behind the lens and absorbs almost twice as much blue light as yellow or red, resulting in a relative insensitivity to shorter wavelengths, a condition exaggerated by age. The light that finally passes through the eye strikes the retina, a small area at the back of the eye densely packed with individual light sensitive receptors connected to the optic nerve, the conduit that transmits and processes visual sensations from the eye to the visual cortex in the brain. It has been shown the light sensitive photoreceptors are of two kinds, rods, which function at night or at very low light levels, and cones, which function under daylight conditions and are the sole source of color perception sensations in humans. The cones are circularly situated at the center of the eye's focal area, the fovea, with the rods forming a ring around the cones.
The notion of “tri” associated with the Trichromatic Generalization arises from the relative sensitivity of the three different cone types generally accepted to be found within the fovea. About 64% of cones exhibit peak sensitivity to 575 nm wavelength light and are said to be red sensitive, though the 575 nm bandpass is actually perceived as yellow. Thirty two percent of cones are considered green, most sensitive to 535 nm light, and only two percent are blue, having a peak response at about 445 nm. It is generally believed analyzing the ratio of the neural activities generated by visually stimulating the three different photoreceptors is the method by which the human visual system interprets color. In practice, it has been shown that the channels of information from the three cones are transformed into three new so-called opponent channels, transmitting a red to green ratio, a yellow to blue ratio and a brightness factor, based upon red and green only, to the brain's visual cortex (as illustrated in FIG.
2
). The physiological sensations produced by visual stimulus is thought to be correlated with stored psychological perceptions, creating color vision.
The above described physiology allows perception of the physical aspects of color, electromagnetic radiation found between the wavelengths of 380 nm and 780 nm, referred to here as human-visible light. Physically, color perception varies according to the wavelength of the visual stimulus. Wavelength is calibrated in nm (nanometer) denominated units, with groups or multiple wavelengths described as bandwidth. When the bandpass of the bandwidth is narrow, the resulting perceptions are associated with pure, or highly saturated, color. As the observed bandpass widens, the color appears less pure. Observers with normal color vision generally identify pure blue as light with a wavelength of about 470 nm, pure green as light with a wavelength of about 505 nm, pure yellow as 575 nm light, and pure red as 610 nm light. However, individual observers often respond differently to the same specimen, so what is a pure color to one may not be perceived that way by another observer.
Besides wavelength, other important physical attributes of visible light are luminance, illuminance, transmittance (reflectance) and metamerism. Luminance accounts for light emitted, such as from a computer display, calibrated in units that reflect the eye's uneven sensitivity to different wavelengths. Illuminance is a measurement of the amount of light that falls on an observed object and transmittance (reflectance) is the measurement of light photons that are absorbed and regenerated as new photons in proportion to the amount of original photons that transmitted through (reflected off) the surface of the object. Various wavelengths of light that are absorbed and retransmitted through (reflected off) a measured image (or specimen) and presented as a percentage of the wavelengths of light that initially struck it can be described as the image's (specimen's) characteristic spectral transmittance (reflectance) curve (for example, as illustrated by FIG.
3
), and plotting and transforming this curve for the purpose of matching colored specimens is a basic aspect of colorimetry. For brevity, we will hereforward refer to transmittance and reflectance simply as transmittance.
It is useful to consider that the reproduction of a colored image may be thought of as an exercise in color matching which takes into account the spectral power distribution of the light source (ie: viewing conditions) illuminating the original, the characteristic curve of the original, the power distribution of the light source illuminating the reproduction, and the characteristic curve of the reproduction. When the characteristic curve of the source's power distribution is combined with the spectral transmittance of the specimen, a visual stimulus is created which triggers color perception. Mathematically characterizing the color perception triggered by the combination of a source's power distribution and a specimen's transmittance curve is a necessary first step in successfully reproducing the perception.
There is, however, a phenomenon that impacts color perception and therefore color reproduction; metamerism. To illustrate the phenomenon, consider two specimens with identical characteristic curves. They will appear to the average observer to match under any source of illuminance. Now, consider two specimens with different curves. They will appear to vary with regards to one another as the source of the illumination is varied. However, there can be two specimens that appear to match despite having different characteristic curves. This is metamerism. An example of metamerism is when the two specimens with different characteristic curves are observed under different sources of illumination, and a match is observed under one of the sources (as illustrated, for example, in FIG.
4
). Because the reproduction of colored images entails taking into account different viewing conditions and media, the mathematical characterization of a color perception destined for reproduction must take into
Katten Muchin Zavis & Rosenman
Lee Cheukfan
LandOfFree
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