The replacement of one image by another during a period of time by the motion of a boundary separating the visual parts of the two images.

• 在图象显示期间，一幅图象由另一幅图象取代。同一屏幕上，两幅图象的可见部分有一分界线，移动这一分界线，把一幅图象逐渐抹掉(划出), 逐渐显示另一幅图象(划入)。