Facsimile and static presentation processing – Natural color facsimile – Color correction
Patent
1995-03-30
1998-07-28
Boudreau, Leo
Facsimile and static presentation processing
Natural color facsimile
Color correction
358522, 358523, 358524, G03F 308, H04N 146
Patent
active
057869081
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to color matching and, more particularly, to a process and related apparatus for converting color values between color spaces.
2. Description of Related Art
The primary use of this invention is in the field of computer assisted color publishing systems particularly in the area of color matching and color reproduction. In such systems typically a color image is scanned using a scanning device which measures light intensity reflected or transmitted from the image to generate electronic signals representing three achromatic images of the original, each of the three achromatic images resulting from detecting the light intensity from the original color image through a colored filter. The filters used are almost always Red Green and Blue. The electronic signal from the scanner is converted to a digital signal in which light intensity levels are represented as numbers. Information identifying each set of numbers representing the image information obtained through each filter is also preserved. Thus, the original colored image has been converted to a plurality of image values, and for each picture element in the picture there is a color value comprising the achromatic component values, i.e., a Red, a Green and a Blue value.
The output of the scanner is eventually used to drive a film exposing device to produce color separation transparencies that are used to make printing plates which in turn are used on a press to supply a printed copy. For purposes of this invention we will refer to this device as a printer and will assume that such printer may be the combination of elements including the color separation transparencies, the plates and the press, or a device such as a color laser printer which may produce a color image without need for a separate printing plate, or any other device which is able to receive an electronic signal representing amounts of inks of given color needed to be printed for each picture element to produce a color image output. Typically such signals are identified as YMCK for the usual four color reproduction situation, each letter corresponding to each of the four inks used, namely Yellow, Magenta, Cyan and Black. Thus, "printer" within this invention includes any device that receives an electronic signal and displays therefrom a colored image.
Scanners are manufactured by a number of manufacturers, each using a particular set of Red, Green and Blue filters. Furthermore, the manufacturers of printers each have their own manner of interpreting the color information at the printer input and applying the proper amount of ink on the paper or colorant in the display.
As anyone who has attempted to describe color knows, such description is complicated by the fact that color perception varies with both the surrounding colors and the illumination used to view an image. Colorimetry, which is the study of color based on both spectral distribution of the energy reflected or transmitted from a test sample and the response of the human eye, as well as the spectral distribution of the illuminating source, provides us with a method to describe and measure color and enables us to determine when colors match. CIE (the International Commission on Illumination) defines Tristimulus values as the amounts of three primary lights which when added produce a visual, or calorimetric, match with an original color. These CIE Tristimulus values can be used for color description and matching purposes. If two colors have the same three CIE Tristimulus values that is if the Red Tristimulus value of one color is the same as the Red Tristimulus value of the other, and so on for the Green and Blue Tristimulus values, then the appearance of the two colors will be the same to the average observer.
Thus, the Tristimulus values are device independent color values.
It would, thus, appear that if one wanted to match colors between input and output using devices from different manufacturers, one would simply need a conversion device to convert the Red, Gr
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Boudreau Leo
E. I. Du Pont de Nemours and Company
Grant II Jerome
Magee Thomas H.
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