Abstract: A method for registering at least two colors for a machine for printing plate elements equipped with at least two printing units: printing marks of different colors in spaced pairs on edges of the plate elements; detecting position errors between different marks of possibly the same color and comparing the position with respective theoretical relative positions; adjusting operation of the printing units to have both marks of a color overlie.

Abstract: A device for adjusting the position of a printing unit with respect to a printing web in a rotary printing machine comprising a control unit operable for controlling the movement of the printing unit from a predefined initial position Pi to a predefined end position Pf by successive steps T. A vision system is operable for capturing images of the formats (F) which are successively printed on the printing web between the initial position Pi and the end position Pf. A calculation unit is operable for evaluating the images and for determining the position Popt of the printing unit at which the images are identical and additionally the position at which the grayscale of the pixels of each image are identical.