Ink control in printing press

A printing press for printing sheets on the basis of first image data comprising:

• plate making means for adding color chart image data expressing a predetermined color chart to said first image data to generate combined image data, and forming an image corresponding to said combined image data on a printing plate,
• ink feed means capable of changing ink feed rates of ink supplied onto a plurality of regions of said printing plate,
• reference color data storage means for storing a numerical value of each color included in said color chart in a predetermined color coordinate system as reference color data,
• image-detecting means for detecting an image of the color chart on said printing sheet transferred from said printing plate to thereby obtain second image data,
• print color data operating means for converting said second image data into said color coordinate system to obtain print color data,
• differential data operating means for comparing said reference color data with said print color data to obtain differential data,
• correction data operating means for obtaining correction data of said ink feed rate with respect to each of said plurality of regions, on the basis of said differential data, and
• control means for controlling the amount of ink to be fed onto said plurality of regions by said ink feed means on the basis of said correction data.