Print tone measuring method

1. A print tone measuring method for obtaining data for controlling ink feeding rates of a printing machine by comparing data of control points in image data obtained by reading an image of reference paper and data of control points in image data obtained by reading an image of an actual print, said method comprising:

a reference paper reading step for reading the image of the reference paper to obtain first image data;

a designated control point setting step for setting designated control points to said first image data for use in measuring the print, said designated control points being set to respective regions on the reference paper corresponding to ink keys of the printing machine;

a first reference point setting step for setting a pair of first reference points to said first image data for specifying image positions;

a print reading step for reading the image of the actual print to obtain second image data;

a second reference point setting step for setting a pair of second reference points to said second image data to correspond to said first reference points;

a first calculating step for calculating, from said first reference points and said second reference points, positions of corresponding control points in said second image data corresponding to said designated control points in said first image data, for the respective regions corresponding to the ink keys of the printing machine;

an extracting step for extracting image data adjacent each of said designated control points and image data adjacent each of said corresponding control points;

a correcting step for correcting the position of each of said corresponding control points in said second image data by comparing the image data adjacent each of said designated control points and the image data adjacent each of said corresponding control points;

a first selecting step for comparing image data including each of said designated control points, of each of the regions corresponding to the ink keys of the printing machine, among the image data adjacent the designated control points in said first image data, with a plurality of templates having different pixel arrangements, selecting a template closest to the image of the region including each of said designated control points, and selecting pixels corresponding in position to pixels arranged in the selected template, as relevant pixels in said first image data;

a second selecting step for selecting, from the corresponding control points corrected, positions of relevant pixels in said second image data corresponding to the relevant points in said first image data, for the respective regions corresponding to the ink keys of the printing machine; and

a second calculating step for calculating data for controlling the ink feeding rates of the printing machine by comparing color values of the relevant pixels in said first image data and color values of the relevant pixels in said second image data for the respective regions corresponding to the ink keys of the printing machine.

2. A print tone measuring method as defined in claim 1 , wherein said second calculating step is executed to determine an average of the color values of the relevant pixels selected in said second selecting step as a color of the control points.

3. A print tone measuring method as defined in claim 2 , wherein said first selecting step is executed to calculate a distribution of pixels in the image of the region including each of said designated control points, corresponding to the pixels arranged in said templates, and to select a template closest to the image of the region including each of said designated control points.

4. A print tone measuring method as defined in claim 2 , wherein said first selecting step is executed to select, as relevant pixels, those pixels in the image data adjacent each of said control points, which are within a predetermined range of color differences with respect to a color of the control point.

5. A print tone measuring method for obtaining data for controlling ink feeding rates of a printing machine by comparing first image data serving as a reference and second image data obtained by reading an image of a print actually made by the printing machine, said method comprising:

a control point setting step for setting positions of control points to said first image data;

an extracting step for extracting image data adjacent said control points from said first image data;

a selecting step for comparing image data including said control points among the image data adjacent the control points in said first image data, with a plurality of templates having different pixel arrangements, selecting a template closest to the image of the region including said control points, and selecting pixels corresponding in position to pixels arranged in the selected template, as relevant pixels in said first image data;

a print reading step for reading the image of the actual print to obtain second image data; and

a calculating step for calculating data for controlling the ink feeding rates of the printing machine by comparing color values of the relevant pixels in said first image data and color values of relevant pixels in said second image data corresponding to the relevant pixels in said first image data; wherein

said calculating step is executed to determine an average of the color values of the relevant pixels selected in said second selecting step as a color of the control points; and

said selecting step is executed to calculate a distribution of pixels in the image of the region including each of said designated control points, corresponding to the pixels arranged in said templates, and to select a template closest to the image of the region including each of said designated control points.

6. A print tone measuring method as defined in claim 5 , wherein said selecting step is executed to select, as relevant pixels, those pixels in the image data adjacent each of said control points, which are within a predetermined range of color differences with respect to a color of the control point.