Apparatus for converting digital chrominance signals of a cartes

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358 11, 358 31, 364731, G06F 1520, G06F 7548, G01J 346

Patent

active

045009724

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION

The invention relates to electronic reproducing technology, particularly to color correction and color recognition.


UNDERLYING PRIOR ART

In electronic reproduction technology, three color components are obtained by means of point-by-point optoelectronic and trichromatic scanning of a master or color, said color components forming the red, green and blue color components of the scanned image points.
The color components represent the coordinates of the respective color in the three-dimensional color space.
In color correction, the measured color components are corrected and the color separation signals required for the production of color separations are derived therefrom, said color separation signals being a measure for the amounts of printing ink required in later printing.
In color recognition, the measured color components are investigated as to their appertaining to one of the color recognition spaces circumscribed within the color space.
The color components can correspond to the three primary measured color value signals, to the chrominance and luminance signals or, on the other hand, can correspond to the tint, saturation and luminance signals. The primary measured color value signals are the cartesian coordinates of the RGB color space and the chrominance and luminance signals are the corresponding cartesian coordinates of the chrominance-luminance color space. The tint, saturation and luminance signals represent the cylindrical coordinates of the tint-saturation-luminance color space, whereby the tint signals form the angles, the saturation signals from the radii and the luminance signals form the third coordinates.
It often proves particularly advantageous to employ the tint, saturation and luminance signals instead of the measured color value signals or instead of the chrominance and luminance signals. In this case, the cartesian color coordinates must be converted into cylindrical color coordinates or polar color coordinates. It is known to undertake such coordinate transformations by means of analog function generators. Said analog function generators, however, have the disadvantage that they are complicated, function unstably and have a low operating speed.


SUMMARY OF THE INVENTION

It is therefore the object of the present invention to specify a digital transformation circuit for the conversion of digital chrominance signals of a cartesian color coordinate system into digital tint and saturation signals of a polar color coordinate system with which the disadvantages of the known, analog function generators can be avoided.
Given the present invention, this object is achieved in that a second cartesian color coordinate system (8) proceeding parallel to the first cartesian color coordinate system (1) is placed through the center point (P'.sub.o) of the polar color coordinate system (4), said second cartesian color coordinate system (8) subdividing the polar color coordinate system (4) into four quadrants, whereby quadrant identification numbers are allocated to the quadrants; in that the quadrants into which the digital chrominance signals (X; Y) fall are identified and the appertaining digital quadrant identification numbers are marked; in that the chrominance signals (X; Y) are converted in valves into corresponding coordinate values (X'; Y') of one of the quadrants; in that the saturation signals (S) is determined from the coordinate values (X'; Y') according to the equation equation the marked quadrant identification numbers and from the tint signals (T*) of the quadrants. c.sub.1 and c.sub.2 are constants or scale factors between the second color coordinate system 8 and the polar coordinate system illustrated in FIG. 2.
It is provided in an advantageous manner that increasing digital quadrant identification numbers are allocated to the individual quadrants in the direction of increasing tint signals (T*) and that the marked quadrant identification numbers respectively form the most significant bits of the tint signals (T) to be determined for all qua

REFERENCES:
patent: 3952187 (1976-04-01), Robinson et al.
patent: 4080655 (1978-03-01), Burger et al.
patent: 4110826 (1978-08-01), Mollgaard et al.
patent: 4306296 (1981-12-01), Blaschke

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