公开(公告)号：JPH04316091A

公开(公告)日：1992-11-06

申请号：JP35066391

申请日：1991-12-12

Applicant: APPLE COMPUTER

Inventor： UIRIAMU DOUSON ,  DEIIN DORAKO

IPC: G06F3/14 ,  G06F3/048 ,  G09G5/00 ,  G09G5/02 ,  G09G5/08

Abstract: PURPOSE: To easily tell an overlay image of a cursor, etc., on a computer output display screen from a background by varying the color values of the pixels of an overlay, according to the color values of the background image. CONSTITUTION: Information on each position of the overlay is generated from mask information stored in an overlay memory 14. The mask information is used to generate a threshold value for contrasting background pixels Pb from a frame buffer 13 with overlay pixels Pc from the memory 14. When the color values of the background pixels are larger than the threshold value, the color values of the pixels of the overlay are set to a minimum value for a specific color, but when it is not, the color values are set to a maximum value.