Method and device for controlling processes during printing

A method for process control during printing, comprising the steps of:

• recording a digital image of a substrate detail comprising a portion of a printing substrate;
• determining a frequency distribution of gray values of image points of the recorded digital image;
• defining, from a central range of the frequency distribution of gray values, the minimum frequency of the frequency distribution of gray values as a limiting value GG of the gray values;
• and
• calculating a half-tone value R of the substrate detail, said step of calculating including counting the image points in the digital image which lie on one side of the limiting value GG as covered and counting the image points in the digital image which lie on the other side of the limiting value GG as free.

An apparatus for image acquisition on a printing substrate, comprising:

• an electronic camera module;
• an imaging objective which is arranged between said camera module and the printing substrate to be imaged;
• and
• an illumination device for illuminating the printing substrate, said illumination device comprising a bright field light source and a dark field light source, each of said bright field light source and said dark field light source being independently activatable and said each of said bright field light source and said dark field light source having an independently adjustable light intensity.