Method and circuit arrangement for selective correction of hues and colors

Claim 3

A method according to claim 1 including the step of acquiring the selective correction signals Y K , M K , C K from a combination of at least one of the limited signals T*, S*, L* with at least one of the signals T', S', L'.

Claim 4

A method according to claim 1 wherein before the selective correction, (a) determining a color locus F 0 of the hue T 0 to be selectively corrected by color value signals R 0 , G 0 , B 0 ; (b) transforming the color locus F 0 of the hue T 0 to be corrected into a chrominance plane of the chrominance/luminance color space by a first transformation of its color value signals R 0 , G 0 , B 0 into chrominance values x' 0 , y' 0 such that a transformed color locus F' 0 of the hue T 0 lies on one of the axes of an X'Y' color coordinate system in the chrominance plane, and retaining transformation coefficients required for the transformation; (c) continuously transforming color loci F of hues of the scanned colors into the chrominance plane by a second transformation of the measured color value signals R, G, B into chrominance values x', y', the color loci F being transformed into the chrominance plane with the previously identified transformation coefficients; (d) selecting those chrominance values x', y' whose corresponding, transformed color loci F' lie in a same half of the X'Y' color coordinate system as the transformed color locus F' 0 of the hue T 0 to be selectively corrected; (e) acquiring a quotient of absolute values of the selected chrominance values x', y' for formation of the hue signal T', the quotient respectively corresponding to a tangent of an angle β described by a corresponding axis and a connecting line between coordinate origin and transformed color locus F' of the hue of a scanned color, the hue signal T' being a measure for a respective absolute value-wise hue deviation of the hue of a scanned color from the hue T 0 to be selectively corrected; and (f) acquiring the limited hue signal T* by a combination of a substantially constant auxiliary control signal H and the hue signal T', said limited hue signal T* having its highest value when scanning the hue T 0 to be selectively corrected and having a value zero when scanning a hue having a prescribed, maximum hue deviation, whereby a sector-shaped hue region is defined around the hue T 0 to be selectively corrected.

Claim 5

A method according to claim 3 wherein the auxiliary control signal H is dependent on the color saturation of the scanned colors in the color original.

Claim 6

A method according to claim 4 wherein the auxiliary control signal H is zero from a color saturation zero up to a boundary color saturation x g which defines an expanse of a gray region around a luminance axis Z of the chrominance/luminance color space, and has a constant value H 0 from the boundary color saturation x g up to a maximum color saturation.

Claim 7

A method according to claim 3 including the step of deforming the hue signal T' before a combination with the auxiliary control signal H.

Claim 8

A method according to claim 1 including the step of determining color value signals of the hue T 0 to be selectively corrected by opto-electronic measurement of a corresponding hue in the color original.

Claim 9

A method according to claim 1 including the step of setting a prescribed maximum hue deviation from the hue T 0 to be selectively corrected by amplitude modification of the chrominance values y' perpendicular to the corresponding axis.

Claim 10

A method according to claim 1, including the step of setting a prescribed maximum hue deviation from the hue T 0 to be selectively corrected by amplitude modification of the hue signal T'.

Claim 11

A method according to claim 1, including the step of setting the prescribed maximum hue deviation from the hue T 0 to be selectively corrected by amplitude modification of the auxiliary control signal H.

Claim 12

A method according to claim 1, including the step of acquiring the limited hue signal T* by forming a difference between the auxiliary control signal H and the hue signal T'.

Claim 13

A method according to claim 1, including the step of transforming measured color value signals R 0 , G 0 , B 0 as color value signals of a color locus F 0 of the hue T 0 to be selectively corrected into chrominance values x' 0 , y' 0 by the steps of: (a) matrixing the color value signals R 0 , G 0 , B 0 into chrominance values x 0 , y 0 of an XY color coordinate system in a chrominance plane corresponding to a transformation of the RGB color space into the chrominance/luminance color space according to the equations x.sub.0 =a.sub.11 R.sub.0 +a.sub.12 G.sub.0 +a.sub.13 B.sub.0 y.sub.0 =a.sub.21 R.sub.0 +a.sub.22 G.sub.0 +a.sub.23 B.sub.0 (b) and by a coordinate rotation of the chrominance values x 0 , y 0 of the XY color coordinate system into the chrominance values x' 0 , y' 0 of an X'Y' color coordinates system rotated by an angle α relative to the XY color coordinate system, said coordinate rotation being dependent upon a position of a color locus F 0 of the hue T 0 to be selectively corrected within the chrominance plane and corresponding to a rotation of the chrominance/luminance color space around a luminance axis Z by an identified angle α according to the equations x'.sub.0 =x.sub.0 cosα+y.sub.0 sinα y'.sub.0 =-x.sub.0 sinα+y.sub.0 cosα where the angle α as a transformation coefficient is identified such that a transformed locus F' 0 of the hue T 0 to be selectively corrected lies on one of the axes of the X'Y'color coordinate system.

Claim 14

A method according to claim 12 including the step of varying the angle α by an automatic balancing until one of the chrominance values x' 0 , y' 0 in the X'Y' color coordinate system becomes zero so that the angle α 0 thus identified is retained.

Claim 15

A method according to claim 1 including the step of transforming measured color value signals R, G, B of hues of scanned colors into chrominance values x', y' of a transformed color loci F' by the steps of: (a) matrixing the measured color value signals R, G, B into the chrominance values x, y of an XY color coordinate system in the chrominance plane corresponding to a transformation of the RGB color space into the chrominance/luminance color space according to the equations x=a.sub.11 R+a.sub.12 G+a.sub.13 B y=a.sub.21 R+a.sub.22 G+a.sub.23 B (b) and by a coordinate rotation of the chrominance values x, y of the XY color coordinate system into the chrominance values x', y' of an X'Y' color coordinate system by an identified angle α 0 according to the equations x'=x cos α.sub.0 +y sin α.sub.0 y'=-x sin α.sub.0 +y cos α.sub.0.

Claim 16

A method according to claim 1 wherein for generating the color saturation signal S': (a) respectively selecting maximum and minimum measured color value signals from the measured color value signals R, G, B; and (b) forming the color saturation signal S' from the differences between maximum and minimum measured color value signals.

Claim 17

A circuit for selective correction of hues and colors of a color original in the production of color separations, comprising: (a) an opto-electronic scanning element means for generating measured color value signals R, G, B; (b) a first correction circuit means connected to the scanning element means for generating corrected color signals Y, M, C; (c) a second correction circuit means connected to the scanning element means for generating selective correction signals Y K , M K , C K ; and (d) a superimposition stage means connected to the first and to the second correction circuit means for superimposition of the corrected color signals Y, M, C and the selective correction signals Y K , M K , C K ; said second correction circuit means comprising: (i) a transformation circuit means connected to the scanning element means for transforming the measured color value signals R, G, B and measured color value signals R 0 , G 0 , B 0 corresponding to a color locus F 0 of a hue T 0 to be selectively corrected into chrominance values and x', y' and x' 0 , y' 0 respectively of an X'Y' color coordinate system in a chrominance plane of a chrominance/luminance color space; (ii) a selection and absolute value circuit means connected to the transformation circuit means for selection and absolute formation of chrominance values +x', /y'/; (iii) setting means for defining a range around the hue T 0 to be selectively corrected associated with the selection and absolute value circuit means; (iv) a divider stage means in communication with the setting means for formation of a hue signal T' from the absolute values of the selected chrominance values +x', /y'/; (v) a signal generator means for generating an auxiliary control signal H; (vi) means for combining the signal H and signal T' to form a limited hue signal T*; (vii) a color saturation signal generator means connected with the scanning element means for generating a color saturation signal S' from the measured color value signals R, G, B; (viii) a luminance signal generator means connected to the scanning element means for generating a luminance signal L' from the measured color value signals R, G, B; (ix) variable limiter stage means connected following the color saturation signal generator means and the luminance signal generator means for forming a limited luminance signal L* and a limited saturation signal S*; and (x) logic circuit means for formation of the selective correction signals Y K , M K C K based on at least one of the signals T*, L*, S*, T', L', S' for a color correction and based on at least one of the signals T* and T' for a hue correction.

Claim 18

A circuit for selective correction of hues and colors of a color original in the production of color separations, comprising: (a) an opto-electronic scanning element means for generating measured color value signals R, G, B; (b) a first correction circuit means connected to the scanning element means for generating corrected color signals Y, M, C; (c) a second correction circuit means connected to the scanning element means for generating selective correction signals Y K , M K , C K ; and (d) a superimposition stage means connected to the first and to the second correction circuit means for superimposition of the corrected color signals Y, M, C and the selective correction signals Y K , M K , C K ; said second correction circuit means comprising: (i) a transformation circuit means connected to the scanning element means for transforming the measured color value signals R, G, B and measured color value signals R 0 , G 0 , B 0 corresponding to a color locus F 0 of a hue T 0 to be selectively corrected into chrominance values and x', y' and x' 0 , y' 0 respectively of an X'Y' color coordinate system in a chrominance plane of a chrominance/luminance color space; (ii) a selection and absolute value circuit means connected to the transformation circuit means for selection and absolute formation of chrominance values +x', /y'/; (iii) setting means for defining a range around the hue T 0 to be selectively corrected associated with the selection and absolute value circuit means; (iv) a divider stage means in communication with the setting means for formation of a hue signal T' from the absolute values of the selected chrominance values +x', /y'/; (v) a signal generator means for generating an auxiliary control signal H; (vi) means for combining the signal H and signal T' to form a limited hue signal T*; (vii) a color saturation signal generator means connected with the scanning element means for generating a color saturation signal S' from the measured color value signals R, G, B; (viii) a luminance signal generator means connected to the scanning element means for generating a luminance signal L' from the measured color value signals R, G, B; (ix) variable limiter stage means connected following the color saturation signal generator means and the luminance signal generator means for forming a limited luminance signal L* and a limited saturation signal S*; and (x) logic circuit means for formation of the selective correction signals Y K , M K C K based on at least one of the signals T*, L*, S*, T', L', S' for a color correction and based on at least one of the signals T* and T' for a hue correction.