Method and apparatus using a conversion table based on pre-printed color charts for determining half-tone dot percents required to reproduce the color of a color specimen

A method of obtaining half-tone dot percents of color separations necessary for reproducing a color designated by a color specimen, comprising the steps of:

• providing a plurality of color charts on which colors are printed using predetermined combinations of half-tone dot percents;
• optically measuring said plurality of color charts to obtain color chart color information for each of said colors printed on said color charts;
• inputting into a memory means for each of said colors said obtained color chart color information together with the corresponding predetermined combination of half-tone dot percents used to print said each of said colors to thereby create in said memory means a conversion table of color chart color information and a corresponding combination of half-tone dot percents for each of said colors printed on said color charts;
• optically measuring a color specimen designating a color to be reproduced to obtain color information for said color to be reproduced;
• successively comparing said color information obtained from said color specimen with said color chart color information in said conversion table and selecting the color chart color information from said conversion table which most closely corresponds to said color information obtained from said color specimen;
• determining if said selected color chart color information coincides with said color information obtained from said color specimen;
• if said selected chart color information coincides with said color information obtained from said color specimen, selecting the combination of half-tone dot percents corresponding to said selected color chart color information from said conversion table, and using said selected combination of half-tone dot percents for reproducing the color designated by said color specimen;
• and
• if said selected color chart color information does not coincide with said color information obtained from said color specimen, performing an interpolation operation on the basis of the combination of half-tone dot percents in said conversion table corresponding to said selected color chart color information and a plurality of other combinations of half-tone dot percents selected from said conversion table to obtain an interpolated combination of half-tone dot percents corresponding to interpolated color chart color information which more closely corresponds to said color information obtained from said color specimen, and using said interpolated combination of half-tone dot percents for reproducing the color designated by said color specimen.

A method of obtaining half-tone dot percents of color separations necessary for reproducing a color designated by a color specimen, comprising the steps of:

• storing a conversion table of color information and corresponding combinations of half-tone dot percents for reproducing colors represented by said color information in said conversion table;
• optically measuring a color specimen designating a color to be reproduced to obtain color information for said color to be reproduced;
• successively comparing said color information obtained from said color specimen with said color information in said conversion table and selecting the color information from said conversion table which most closely corresponds to said color information obtained from said color specimen;
• selecting the combination of half-tone dot percents corresponding to said selected color information from said conversion table;
• determining if a value of 0% is included in said selected combination of half-tone dot percents, and determining if a value of 100% is included in said selected combination of half-tone dot percents;
• if at least one of said values of 0% and 100% is included in said selected combination of half-tone dot percents, producing an expanded conversion table which includes expanded combinations of half-tone dot percents and corresponding expanded color information, said expanded combinations of half-tone dot percents including a half-tone dot percent value below 0% when said selected combination of half-tone dot percents includes said value of 0% and including a half-tone dot percent value above 100% when said selected combination of half-tone dot percents includes said value of 100%, said expanded color information corresponding to said expanded combinations of half-tone dot percents being based upon the color information included in said conversion table;
• performing an interpolation operation on the basis of said selected combination of half-tone dot percents and a plurality of other combinations of half-tone dot percents to obtain an interpolated combination of half-tone dot percents corresponding to interpolated color information which more closely corresponds to said color information obtained from said color specimen, said plurality of other combinations of half-tone dot percents being selected from said expanded conversion table when at least one of said values of 0% and 100% is included in said selected combination of half-tone dot percents and said plurality of other combinations of half-tone dot percents being selected from said conversion table when neither one of said values of 0% and 100% is included in said selected combination of half-tone dot percents;
• and
• using said interpolated combination of half-tone dot percents for reproducing the color designated by said color specimen.

An apparatus for obtaining half-tone dot percents of color separations necessary for reproducing a color designated by a color specimen, comprising:

• optical measuring means for optically measuring a plurality of color charts on which colors are printed using predetermined combinations of half-tone dot percents and for optically measuring a color specimen designating a color to be reproduced, said optical measuring means being operative to obtain color information for each of said colors printed on said color charts and for said color designated by said color specimen;
• memory means for storing information inputted into said memory means;
• inputting means for inputting into said memory means, for each of said colors, said obtained color information together with the corresponding predetermined combination of half-tone dot percents used to print said each of said colors to thereby create a conversion table of color information and a corresponding combination of half-tone dot percents for each of said colors printed on said color charts;
• means for successively comparing said color information obtained from said color specimen with said color information in said conversion table and for selecting the color information from said conversion table which most closely corresponds to said color information obtained from said color specimen;
• selecting means for selecting the combination of half-tone dot percents corresponding to said selected color information from said conversion talbe;
• and
• means for displaying said selected combination of half-tone dot percents.