Picture color tone controlling method and apparatus

A picture color tone controlling apparatus for a printing press, comprising:

• positional displacement detection means for detecting a positional displacement between a plate making picture position which is a position of a printing picture with respect to printing paper and which is obtained from plate making data and an actual picture position which is a position of a printing picture with respect to the printing paper obtained by detecting actual printing paper printed based on the plate making data by means of a sensor;
• picture position moving means for moving the plate making picture position so as to eliminate the detected positional displacement;
• an ink supplying apparatus for supplying ink to each of regions divided in a printing widthwise direction;
• target color mixture halftone density setting means for setting a target color mixture halftone density for each of ink supplying unit widths of said ink supplying apparatus when the printing picture is divided with the ink supplying unit width based on the information of the moved plate making picture;
• an IRGB densitometer disposed on a feeding line of an actual printing sheet obtained by printing;
• color mixture halftone density measuring means for operating said IRGB densitometer to measure an actual color mixture halftone density for each of the ink supplying unit widths of the actual printing sheet;
• target halftone dot area ratio arithmetic operation means for arithmetically operating a target halftone dot area ratio of each ink color corresponding to the target color mixture halftone density based on a corresponding relationship set in advance between halftone dot area ratios and color mixture halftone densities;
• actual halftone dot area ratio arithmetic operation means for arithmetically operating an actual halftone dot area ratio of each ink color corresponding to the actual color mixture halftone density based on the corresponding relationship between the halftone dot area ratios and the color mixture halftone densities;
• target monochromatic halftone density arithmetic operation means for determining a target monochromatic halftone density corresponding to the target halftone dot area ratio based on a corresponding relationship set in advance between the halftone dot area ratios and monochromatic halftone densities;
• actual monochromatic halftone density arithmetic operation means for determining an actual monochromatic halftone density corresponding to the actual halftone dot area ratio based on the corresponding relationship of the halftone dot area ratios and monochromatic halftone densities;
• solid density difference arithmetic operation means for determining, based on a corresponding relationship set in advance among the halftone dot area ratios, the monochromatic halftone densities and solid densities, a solid density deviation corresponding to a deviation between the target monochromatic halftone density and the actual monochromatic halftone density under the target halftone dot area ratio;
• and
• ink supplying amount adjusting means for adjusting an ink supplying amount for each of the ink supplying unit widths based on the solid density deviation.