Apparatus for converting digital chrominance signals of a cartesian color coordinate system into digital color signals and saturation signals of a polar color coordinate system and a transformation circuit
First Claim
1. A coordinate transformation circuit for converting digital chrominance signals of a first cartesian color coordinate system into digital hue signals and saturation signals of a polar color coordinate system, whereby a second cartesian color coordinate system (8) with axes parallel to the first cartesian color coordinate system (1) is placed through the center point (P'"'"'o) of the polar color coordinate system (4), said second cartesian color coordinate system (8) dividing the polar color coordinate system (4) into four quadrants, which are defined by digital quadrant identification numbers, comprising:
- a. means for converting the pairs of digital chrominance signal values (X;
Y), defining the positions of the color locations (F) within the first cartesian color coordinate system (1) into corresponding pairs of second chrominance signal values (X'"'"';
Y'"'"'), defining the relative positions of said color locations (F) within a selected quadrant of the second cartesian color coordinate system (8),b. means for generating digital hue signal values (T*) for said selected quadrant and saturation signal values (S) from said pairs of second chrominance signal values (X'"'"';
Y'"'"') according to the equations;
space="preserve" listing-type="equation">T*=C.sub.2 arc tan (Y'"'"'/X'"'"') and
space="preserve" listing-type="equation">S=C.sub.1 √
X'"'"'.sup.2 +Y'"'"'.sup.2wherein C1 and C2 are constant factors, andc. means for determining the quadrant identification numbers of the quadrants, in which the respective color locations (F) fall, from said first chrominance signal values (X;
Y), whereby the hue signal values (T) for all quadrants are obtained from said determined quadrant identification numbers and said hue signal values (T*) of said selected quadrant.
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Abstract
A method for converting digital chrominance signals of a cartesian color coordinate system into digital color signals and saturation signals of a polar color coordinate system and including a transformation circuit for the transformation from cartesian to polar coordinates.
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Citations
15 Claims
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1. A coordinate transformation circuit for converting digital chrominance signals of a first cartesian color coordinate system into digital hue signals and saturation signals of a polar color coordinate system, whereby a second cartesian color coordinate system (8) with axes parallel to the first cartesian color coordinate system (1) is placed through the center point (P'"'"'o) of the polar color coordinate system (4), said second cartesian color coordinate system (8) dividing the polar color coordinate system (4) into four quadrants, which are defined by digital quadrant identification numbers, comprising:
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a. means for converting the pairs of digital chrominance signal values (X;
Y), defining the positions of the color locations (F) within the first cartesian color coordinate system (1) into corresponding pairs of second chrominance signal values (X'"'"';
Y'"'"'), defining the relative positions of said color locations (F) within a selected quadrant of the second cartesian color coordinate system (8),b. means for generating digital hue signal values (T*) for said selected quadrant and saturation signal values (S) from said pairs of second chrominance signal values (X'"'"';
Y'"'"') according to the equations;
space="preserve" listing-type="equation">T*=C.sub.2 arc tan (Y'"'"'/X'"'"') and
space="preserve" listing-type="equation">S=C.sub.1 √
X'"'"'.sup.2 +Y'"'"'.sup.2wherein C1 and C2 are constant factors, and c. means for determining the quadrant identification numbers of the quadrants, in which the respective color locations (F) fall, from said first chrominance signal values (X;
Y), whereby the hue signal values (T) for all quadrants are obtained from said determined quadrant identification numbers and said hue signal values (T*) of said selected quadrant. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A coordinate transformation circuit for converting digital chrominance signals of a cartesian color coordinate system into digital hue signals and saturation signals of a polar color coordinate system, whereby a second cartesian color coordinate system (8) with axes parallel to the first cartesian color coordinate system (1) is placed through the center point (Po '"'"') of the polar color coordinate system (4), said second cartesian color coordinate system (8) dividing the polar color coordinate system (4) into four quadrants, which are defined by digital quadrant identification numbers, comprising:
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a. a table memory (12;
12'"'"') for storing digital hue signal values (T*) and saturation signal values (S) calculated from second chrominance signals (X'"'"';
Y'"'"') of a selected quadrant of the second cartesian color coordinate system (8) according to the equations;
space="preserve" listing-type="equation">T*=C.sub.2 arc tan Y'"'"'/X'"'"' and
space="preserve" listing-type="equation">S=C.sub.1 √
X'"'"'.sup.2 +Y'"'"'.sup.2wherein C1 and C2 are constant factors said saturation signal values (S) and said hue signal values (T*) being addressable by said corresponding chrominance signal values (X'"'"';
Y'"'"'), said table memory (12;
12'"'"') having address-inputs and respective hue signal value outputs (37) and saturation signal value outputs (38),b. an inversion stage (10) connected to the address-inputs of the table memory (12;
12'"'"') and supplied with the first digital chrominance signals (X, Y) of the first cartesian color coordinate system (1) for inverting each pair of the supplied first digital chrominance signal values (X;
Y) into a corresponding pair of second chrominance signal values (X'"'"';
Y) of the second cartesian color coordinate system within said selected quadrant;
said second chrominance signal values (X'"'"';
Y'"'"') representing the addresses for said table memory (12;
12'"'"'),c. a quadrant recognition stage (11) supplied with the most significant bits (MSB) of said first digital chrominance signal values (X;
Y) for recognizing the digital quadrant identification number of the quadrant in which each pair of first chrominance signal values (X;
Y) falls at outputs of the quadrant recognition stage (11); andd. an inverter-stage (13) connected to the hue signal value outputs (37) of the table memory (12;
12'"'"') and to the outputs of the quadrant recognition stage (11), said inverter-stage (13), being controlled by said quadrant recognition stage (11), inverting or not inverting the hue signal values (T*) in dependence of the recognized digital quadrant identification numbers, whereby the digital quadrant identification numbers represent the most significant bits (MSB) and the inverted or not inverted hue signal values (T*) of the selected quadrant the least significant bits (LSB) of the digital hue signal values of the polar color coordinate system (4). - View Dependent Claims (14, 15)
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Specification