In a method for determining color and/or density values for use in monitoring and regulating a printing process in a printing apparatus, specifically in a sheet-fed offset printing press, measuring areas of a printed sheet are measured photoelectrically during the printing process, directly in or on the running printing apparatus. From the measured values obtained in the process, the color and/or density values for the relevant measuring areas are formed. From the measurement, measured value deviations caused directly in the printing process with respect to a measurement outside the printing process can be corrected computationally.