Abstract: An image data processing system reproduces a small-sized picture scaled down from an original picture over a large-sized picture on a screen. A switching circuit having an input port is supplied with pieces of first video data information indicative of parts of the original picture and distributes the pieces of first video information to a plurality of output ports thereof. A plurality of line memory circuits are respectively coupled to the plurality of output ports except for one of the output ports and memorize the pieces of first video information. An averaging circuit coupled to the line memory circuits is and the aforesaid one of the output ports and averages values respectively represented by the pieces of first video data information for determining the value of a piece of second video data information indicative of a part of small-sized picture, thereby preventing the small-sized picture from loss of any part of the images incorporated in the small-sized picture.