Method for producing color and black plates in a multi-color plate making apparatus

Claim 1

A method for producing color and black plates in a multi-color plate making apparatus by setting a color-separation curve, the method comprising the steps of: (i) determining a light intensity value X n and a basic light intensity xn from a density information value D n of an arbitrary pixel of a color-film original picture by using photographic density characteristic curves of a photographic film used to form the color-film original picture, and converting the basic light intensity value (xn) into a dot area % value a xn by conducting a tonal conversion according to a formula 1, thereby setting a color-separation curve of a predetermined basic color plate, any one among C, M or Y, other than a black (B) plate, the color-separation curve of the basic color plate being represented by a correlation between the basic light intensity values and the dot area % values; (ii) determining a light intensity value range X BXH -X BXS to set for the black plate and dot area % values a BH -a BS to be set for the color-separation curve of the basic color plate; (iii) determining a light intensity value B xn of the arbitrary pixel in the light intensity value range X BSH -X BXS X BXH -X BXS into a dot area % value a Bxn for the black plate, thereby setting a color-separation curve of the black plate under initial conditions determined in step (ii) by conducting a tonal conversion according to formula (1); (iv) producing the color plate in accordance with the color-separation curve of the basic color plate set in step (i); and, (v) producing the black plate in accordance with the color-separation curve of the black plate set in step (iii); wherein the formula, 1 is presented as follows: a.sub.xn =a.sub.H +α(1-10.sup.-k·xn)(a.sub.s -a.sub.H)/(α-β) (1) where xn: a basic light intensity value represented by xn=X n -X Hn , determined by subtracting a light intensity value X Hn of a brightest area obtained from a corresponding density information value D Hn of the brightest area of the original color-film picture from a light intensity value X n of a pixel obtained from a density information value, D n , of a corresponding pixel of the color-film original picture for a basic color plate, where a brightest area of the black plate should be read as a part-where black is entered (a black starting point); a xn : a dot area % value set to a pixel on color, C, M and Y, and black B, plates corresponding to an arbitrary pixel of an original picture; a H : a dot area % value predeterminedly set to a black starting point of a black plate or a brightest area of respective color plates; a s : a dot area % value predeterminedly set to a part of a black plate where entering of black is finished or a darkest area of respective color plates; α: a surface reflectance of a paper used to produce a printed picture thereon; β: a value determined by β=10 - β ; k: a value determined by k=γ/(X Sn -X Hn ), where X Sn is a light intensity value of a darkest area obtained from a density information value D Sn of the darkest area, S area, of an original picture in a case of a basic color plate, and where X Sn represents a light intensity value of black finishing point in a case of a black plate; γ: an arbitrary coefficient; and xn, n Hn, Sn, H and S should be accompanied with C, M Y, and B in relation to color C, M, and Y, and black B, plates upon conducting tonal conversion formula (1).

Claim 2

A method for producing color and black plates in a multi-color plate making apparatus by setting a color-separation curve, the method comprising the steps of: (i) determining a light intensity value X n and a basic light intensity xn from a density information value D n of an arbitrary pixel of a color-film original picture by using photographic density characteristic curves of a photographic film used to form the color-film original picture, and converting the basic light intensity value (xn) into a dot area % value a xn by conducting a tonal conversion according to a formula 1, thereby setting a color-separation curve of a predetermined basic color plate, any one among C, M or Y, other than a black (B) plate, the color-separation curve of the basic color plate being represented by a correlation between the basic light intensity values and the dot area % values; (ii) determining a light intensity value range X BXH -X BXS to set for the black plate and dot area % values a BH -a BS to be set for the color-separation curve of the basic color plate; (iii) determining a light intensity value B xn of the arbitrary pixel in the light intensity value range X BSH -X BXS X BXH -X BXS into a dot area % value a Bxn for the black plate, thereby setting a color-separation curve of the black plate under initial conditions determined in step (ii) by conducting a tonal conversion according to formula (1); (iv) producing the color plate in accordance with the color-separation curve of the basic color plate set in step (i); and, (v) producing the black plate in accordance with the color-separation curve of the black plate set in step (iii); wherein the formula, 1 is presented as follows: a.sub.xn =a.sub.H +α(1-10.sup.-k·xn)(a.sub.s -a.sub.H)/(α-β) (1) where xn: a basic light intensity value represented by xn=X n -X Hn , determined by subtracting a light intensity value X Hn of a brightest area obtained from a corresponding density information value D Hn of the brightest area of the original color-film picture from a light intensity value X n of a pixel obtained from a density information value, D n , of a corresponding pixel of the color-film original picture for a basic color plate, where a brightest area of the black plate should be read as a part-where black is entered (a black starting point); a xn : a dot area % value set to a pixel on color, C, M and Y, and black B, plates corresponding to an arbitrary pixel of an original picture; a H : a dot area % value predeterminedly set to a black starting point of a black plate or a brightest area of respective color plates; a s : a dot area % value predeterminedly set to a part of a black plate where entering of black is finished or a darkest area of respective color plates; α: a surface reflectance of a paper used to produce a printed picture thereon; β: a value determined by β=10 - β ; k: a value determined by k=γ/(X Sn -X Hn ), where X Sn is a light intensity value of a darkest area obtained from a density information value D Sn of the darkest area, S area, of an original picture in a case of a basic color plate, and where X Sn represents a light intensity value of black finishing point in a case of a black plate; γ: an arbitrary coefficient; and xn, n Hn, Sn, H and S should be accompanied with C, M Y, and B in relation to color C, M, and Y, and black B, plates upon conducting tonal conversion formula (1).