PURPOSE: To superpose a blanking mask and a design easily, accurately and quickly by writing image signals into a memory medium and writing the same in the same address disposition as the address disposition of the memory medium into which the image signals corresponding to contour signals are written.

CONSTITUTION: The images of an original picture cylinder 1 of a color scanner are scanned with a scanning head 4, and the respective signals or red R, green G and blue B from an A/D conversion circuit 13 are converted to the recording signals of cyan C, magenta M, yellow Y and black K with a color operating circuit 15. On the other hand, the contour signal values from a contour signal operating circuit 16 are written as a contour signal l of 1 bit by a mixer circuit 18 into a memory medium 17 into which the image signal (for example, black K) corresponding to the signal l are written in the same address disposition as the address disposition of the medium. The final images are written from the medium 17 into another medium 24 by using a CPU22 for layout and a color monitor 20. A blanking mask is formed on a recording cylinder 7 by using such medium 24.